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Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance (2018)

Chapter: Chapter 4.0 Spot Painting of Steel Bridges

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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 35
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 41
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 42
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 43
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 45
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 46
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 47
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 48
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 51
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 52
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Page 53
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
Page 53
Page 54
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
Page 54
Page 55
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
Page 55
Page 56
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
Page 56
Page 57
Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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Suggested Citation:"Chapter 4.0 Spot Painting of Steel Bridges." National Academies of Sciences, Engineering, and Medicine. 2018. Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25089.
×
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NCHRP Project 14-30 31 4.0 SPOT PAINTING OF STEEL BRIDGES Spot painting of bridges, whether performed by in-house forces or by experienced paint contractors, should have a consistent set of actions to ensure properly applied and well performing coatings. Those action steps are: 1. Mobilize the painting operation 2. Deploy at the work site (field operations) 3. Perform surface preparation 4. Monitor conditions 5. Apply coatings 6. Perform final inspection and repairs 7. Demobilize The work should begin once spot painting projects are planned/scoped. If field assessments have been performed prior to this, there may be sufficient information to determine the specific requirements for each bridge project. 4.1 Mobilize the Painting Operation Mobilization includes a range of preparatory steps to ensure that all factors related to spot painting are addressed prior to fieldwork. The mobilization tasks are: • Scoping/scheduling of projects o Determining bridge locations requiring spot painting o Identifying access restrictions o Locating suitable staging/parking areas adjacent to the bridge o Identifying access equipment requirements o Determining traffic control requirements and developing a traffic control plan o Determining coatings to be used, method(s) of application and material/quantities o Identifying potential conflicts with other agency crews or contractors working at the jobsite • Environmental issues need to be addressed early on. This may entail meetings with regulatory officials, officials of facilities potentially impacted by the work and those of local governments along with nearby residents. Potential environmental issues include: o Sensitive receptors (drinking water inlets, public parks, surrounding urban areas) o Endangered species, raptors o Project commitments to the public/local agencies (e.g. minimum disruption) o Permitting for hazardous waste disposal (if necessary) Environmental clearances may be required prior to the onset of fieldwork. • Worker safety issues need to be addressed including: o A job hazard analysis should be performed addressing health and safety issues including, but not limited to:  Toxicity of the existing coating potentially including lead and other heavy metals, PCBs and any other hazardous materials identified  Hazardous waste classification/required controls for generation, handling, storage and disposal  Review of repair coating SDS information  PPE required

NCHRP Project 14-30 32  Up-to-date training, testing/health screenings, and recordkeeping of workers regarding safe working practices, potential hazards and use of appropriate PPE. o Worker safety requirements are a major issue in mobilizing for painting work. The supervisor must ensure that information regarding hazardous or toxic materials used on the worksite is presented to all worksite participants. The crew supervisor should prepare a hazardous communication plan consisting of:  A written program  A hazardous material list  SDSs and appropriate labelling for waste storage containers. Workers need to receive the plan and have all their concerns addressed. o Some project tasks require the use of competent persons (OSHA) on the jobsite. o Power tools present a range of safety issues depending on type and workers need to be familiar with proper equipment operation and appropriate PPE. • For in-house painting, district shops or garages will probably be used to store coatings prior their use. The following procedures should be followed o If multi-component coatings are to be used, they should be furnished in pre- measured kits from the coating manufacturer. o When the containers are delivered, they should be checked for labelling and damage. Containers with signs of leakage should be returned to the manufacturer for replacement. o Crew supervisors should keep all paperwork and assure its completeness. Batch numbers on the containers should be recorded and matched to the provided paperwork (certifications). Supervisors should also ensure that the proper PDSs and SDSs are present. o In many cases, coatings are acquired and may be stored for some time before application (Figure 7). Shelf life and storage conditions, especially temperature, are critically important and manufacturer guidelines should be complied with both at the DOT shop and in the field (if coatings are stored onsite).  If stored for extended periods, the coating may liver, skin, gel or settle to form a hard layer that will not disperse. In those cases, the coatings should be discarded and replaced. • If coatings have been stored at or slightly beyond the shelf life are to be taken to the Figure 7 Proper storage of coatings at highway agency garage

NCHRP Project 14-30 33 field, at least one container (typically Part A if two-component coating) should be opened and the contents checked. If degraded, the coating should be discarded and replaced. • Prior to the start of the fieldwork, the crew supervisor should prepare a list of all equipment and supplies needed for the work. The potential items for spot painting are provided in Appendix D. All equipment should be inspected and in good condition before being taken to the work site. Supplies should be sufficient to complete work on the project: • Power tools will typically consume cleaning media (needles, sand paper, non-woven discs, and wire brushes) at a high rate. • Coatings are subject to losses (spills, mixing errors, pot life exceedances and application losses) Supervisors should inspect the PPE of the crew to insure it is suitable for continued use. All access equipment should be inspected (in addition to daily inspections while on site). If the jobsite is to be shared with other agency crews or contractors conducting other maintenance work on the bridge, district officials and the painting supervisor will need to coordinate to arrange for proper control and access to the bridge without interfering with each other. Work needs to be sequenced properly: • Work should generally proceed from the top down • Tasks such as deck repair or resealing should precede any maintenance painting work • Attendant work involving abrasive cutting, welding or torch cutting should be performed prior to paint work or kept away from potential sources of ignition/explosions related to the spot painting work (e.g., wind screens, ground cloths, solvents and solvent vapors). After all environmental clearances are obtained and the equipment and materials are assembled (and worker testing completed), the fieldwork can proceed. A preliminary trip to the worksite immediately prior to the fieldwork is recommended for identifying any changed conditions, such as recent rainfall, that might delay a project due to unsatisfactory site conditions. The supervisor should check the weather forecast and determine whether it will conform to restrictions contained in the coating PDSs and agency standards before moving to the jobsite. 4.1.2 Deployment at the Work Site Deployment at the work site includes all tasks prior to actual spot painting work on bridges. Those tasks entail: • Establishing traffic control (if necessary) • Initiating painting support activities in the staging area • Creating a waste storage site (if necessary) • Performing necessary site clean-up • Placing access equipment at repair sites • Installing necessary waste containment • Establishing work areas

NCHRP Project 14-30 34 Traffic control — Necessary traffic control devices including flagging crews should be provided along with an approved traffic control plan. Once proper traffic control is in place (signs, delineators, crash barriers, and flagging), the painting crew can begin painting operation. Staging areas — When workers arrive at the worksite staging area, the supervisor should point out potential hazards, including those related to traffic and working on the bridge and any environmentally sensitive locations that need to be avoided. It is most desirable to establish staging areas behind guardrails if possible. Equipment and consumable supplies can be bought to the staging area in trucks and off-loaded and located as necessary for a day’s work. Typically, coating mixing and operation of generators, compressors and pressure washers take place in the staging area. Combustible materials should be properly stored and kept away from sources of ignition. Locations for mixing coatings should be identified in reasonable proximity to the painting operations. It may be more suitable to perform mixing operations in a truck bed (Figure 8). In some cases, access issues may require lane closures for use as staging areas or location of access equipment. Waste storage sites — A fenced in, placarded storage area is required for hazardous wastes stored on site (Figure 9). It can be located on the highway right-of- way, or in some cases at agency garages if permitted by the state DNR. Site cleanup — Accumulated trash around the bridge should be collected prior to setting up painting operations (Figure 10). A useful early action is to perform clean-up of the site adjacent to forthcoming painting operations to rid them of trash, debris, adjacent plants/tree limbs, and accumulations of bird droppings that would interfere with the painting operations and to conduct any preliminary environmental assessments actions that might be warranted. Included should be soil lead analysis if concern exists. If paint deterioration or previous painting operations have resulted in paint chips lying on the ground around the bridge, they should be collected, especially if they contain lead. Figure 8. Paint mixing setup mounted in a truck next to bed alongside of a spray pump

NCHRP Project 14-30 35 Access equipment — The initial work will consist of installing access equipment, including ladders, pick boards, scaffolds, mobile lift devices (e.g., bucket trucks, boom lifts, scissors lifts and under bridge platforms — Figure 11). Proper tie offs are required for workers over six feet off the ground (with the possible exception for workers on ladders). Waste containment — Use of power tools with vacuum shrouds will usually reduce or eliminate the need for full containment of surface preparation operations when existing coatings contain lead. It may be necessary to place drop cloths on the ground under the work area to capture debris generated in the initial cleaning steps. If the work area below the bridge is over water or inaccessible, a suspended diaper can be used (Figure 12). Where possible, ground cloths/tarps can be spread under surface preparation areas to catch debris and paint spills (Figure 13). If work is performed over traffic, steps must be taken to isolate the vehicles from the work activities (including any potential overspray or paint spillages). Wind curtains or full containment may be required if paint application work can generate overspray damage to adjacent vehicles or property. Figure 9. Small hazardous waste site on highway right-of-way Figure 10. Trash on a bridge abutment needing removal before painting operations begin Figure 11. Worker removing paint from under bridge platform

NCHRP Project 14-30 36 Work areas – When spot painting involves existing lead paint, it may be necessary to rope off the work area and prevent public access. Once access and containment have been installed, hoses and power chords can be placed between the generators, compressors, spray pumps and pressure washers prior to the onset of work. Determine whether additional lighting is needed for sheltered areas or inside containments based upon SSPC Guide 12, “Guide to Illumination of Industrial Coating Projects,” from surface preparation through final inspection. Table 2 of SSPC Guide 12 provides ratios of lighting between task areas and darker and lighter surroundings. Special requirements are provided for working in confined spaces or where solvent vapors might pose explosion/ignition hazards. Lighting on the work surfaces should exceed 10 ft.-candles (108 Lux) for general work, 20 ft.-candles (215 Lux) for surface preparation and painting and 50 ft. candles (538 Lux) for inspection. 4.1.3 Inspection Requirements The work should include hold points prior to each successive step in the painting process for inspections (either by the supervisor or for work performed by contract, the agency’s inspector). These include: • Pre-surface preparation • Post-surface preparation • Coating conditions for application (each coating) • Coating application (each coating) • Post-application of coating • Post-curing • Final inspection Pre-surface preparation inspection precedes the work. It should include visual inspection to detect grease, tar or oil deposits, metal imperfections (e.g. scabs, weld splatter, slivers), inaccessible areas and other problem areas. Post-surface preparation inspection verifies the degree of cleanliness and surface profile (for SSPC SP 11 and 15 power tool cleaning). Figure 12. Bib suspended under a bridge to collect wastes generated Figure 13. Ground cloth placed under spot painting work area

NCHRP Project 14-30 37 Coating conditions for application inspection occurs just prior to coating application. It ensures that a surface has not been re-contaminated and that the prevailing ambient conditions and surface temperature are acceptable before the coating is mixed. Coating application inspection is performed during application and includes ambient conditions, wet film thickness (WFT) readings and detection of any defects in the wet film. Post-coating application inspection follows the application of each coat of paint. It is used to check the dry film thickness (DFT) to determine whether it is within the specified range. It is used to determine if each coat is ready to receive the next coat (within the manufacturer’s recoat window and after verifying it is free from contamination). Any imperfections such as overspray, pin-holing, insufficient/excessive film build should be corrected prior to top coating. Post-cure inspection will verify that the final DFT of the coating has been achieved and that no film defects/misses are present. Final inspection will verify that all coating touch-ups or other corrective actions have been made. 4.1.4 Surface Preparation To receive coatings, substrates must be properly cleaned, including: removing loose chalked paint, soils, bird droppings, loose and stratified rust, and oils/greases/tar. Proper surface preparation for spot painting should consist of four tasks. In order of performance those are: 1) solvent cleaning, 2) hand tool cleaning, 3) washing/soluble salt treatment, and 4) power tool cleaning. Task 1 Solvent Cleaning — The initial cleaning of the repair area should be done in accordance with SSPC-SP 1, “Solvent Cleaning” to remove all visible oil, grease, soil, and other soluble contaminants (e.g., tar) from surfaces to be painted. Diesel fume residues are commonly found on lower flanges of beams and girders on overpass bridges over roads and railways. Prior to solvent cleaning, areas to be spot painted should be initially cleaned by brushing with stiff fiber or wire brushes with appropriate cleaners followed by a water rinse. For solvent cleaning heavy build-ups of tar, oil, or grease can be removed using scrapers. The remaining material can be removed from the contaminated surfaces by one of the following treatments: • Wiping with rags or brushes wetted with solvent followed by a final wiping with clean solvent and clean brushes or rags • Spraying the surface with solvent followed by a final solvent spraying • Vapor degreasing using stabilized chlorinated hydrocarbon solvents • Substituting emulsion cleaners in place of the methods described. After treatment the surface should be washed with fresh water or steam to remove harmful residues. • Steam cleaning using detergents or cleaners followed by fresh water or steam washing to remove harmful residues. After solvent cleaning, dirt, dust, and other remaining contaminants are removed by brushing, blow down by clean dry air or vacuuming. Vacuuming should be used where lead-based coatings are present. When water/steam/detergents are used, potable water should be used. It is recommended that after solvent cleaning, the affected areas should be tested for residual surface contamination of oils, tars or greases per ASTM F22 “Standard Test Method for

NCHRP Project 14-30 38 Hydrophobic Surface Films by the Water Break Method.” Alternatively, ultraviolet (black) light can be used to detect residual hydrocarbon films. Task 2 Hand Tool Cleaning — Hand tool cleaning per SSPC-SP 2, “Hand Tool Cleaning,” can be used to remove: • Loose peeling paint • Stratified/pack rust and • In lieu of power tool cleaning, loose surface rust and debris. Hand tools include scrapers, hammers and chisels (Figure 14). Adherent materials that cannot be removed with a dull scraper are deemed acceptable under that specification. The guide permits the use of impact hand tools such as chisels or small sledge hammers to remove stratified rust. Wire brushing, abrading (sand paper or abrasive pads), hand scraping, or other non-impact methods are used to remove all loose mill scale, all loose or non-adherent rust, and all loose paint. The SSPC visual reference standard, SSPC-VIS 3, “Guide and Reference Photographs for Steel Surface Prepared by Power and Hand Tool Cleaning,” provides reference photographs of typical “before” and “after” conditions showing common surfaces treated by power and hand tools and their respective appearances after cleaning. Hand wire brush cleaning is the standard used for SP 2 cleaning in the “after” reference photographs in SSPC-VIS 3. If the entire repair area involves an inter-coat failure of the existing coating and the primer or intermediate coats remain, the exposed coating can be lightly sanded using 100 to 200 grit sandpaper to provide adhesion for the repair coating. Potable Water Care should be exercised when specifying potable water for bridge washing. Drinking water from municipal water plants can have elevated levels of chlorides used to treat minerals. For potable water, Caltrans limits the chloride content to 75 ppm and the sulfate content to 200 ppm. Stratified and Pack Rust Stratified rust occurs on a surface and consists of tightly adherent rust layers that may be up to and greater than 1” thick. Pack rust commonly forms between mating plates and as it expands, the plates are deformed (e.g. riveted members). Due to their tight adherence, they must be removed by impact methods. Hand tools used include hammers, sledge hammers and chisels. One effective way to use hammers is to strike the backside of the corroded member and have the resulting shock break loose large pieces of rust. Impact power tools such as chipping hammers, scabblers, needle guns and flappers can also be used. At least one highway agency is using high-pressure washing to remove pack rust. Once it is loosened, pack rust can be dislodged with chisels, air lances or pressure washers (followed by drying prior to painting).

NCHRP Project 14-30 39 Even if SSPC SP 3 cleaning is specified, when encountering failed areas only possessing exposed paint, it is best to use this process if the exposed paint is adherent. The boundary around the failed coating area should be feathered by hand sanding. The sanded areas can be dry wiped using a coarse cloth (burlap) to remove any remaining soils and chalk from the existing topcoat prior to painting. Vacuuming or a blow-down using compressed air (if no lead is present) can also be used if the existing coating at the border of the repair is not chalked. Task 3. Washing/Soluble Salt Treatment — Soluble salts may be present in spot repair areas in concentrations that will result in premature failures of applied coatings. Dry surface preparation/cleaning methods, including hand-tool cleaning, power-tool cleaning and abrasive blasting, may not adequately remove soluble salts. Tolerable salt limits depend upon the type of service (atmospheric or immersion) and the severity of the environment. Field salt concentrations are either expressed as concentrations (µg/cm2) or conductivity (µS/cm). Those values are typically obtained from field measurements using wet extractions performed on test surfaces using the sleeve method (proprietary) or the patch method (Bresle) method. The sleeve extraction fluid can undergo several tests to indicate specific soluble salt ion concentrations (chlorides, nitrates, sulfates and ferrous-related abrasive blasting). In some environments, testing for chloride ions may be sufficient. For industrial atmospheres nitrate and/or sulfate ion tests may be necessary as well. The conductivity test uses a conductivity meter and is general for all ions present. Allowable soluble contamination thresholds are typically established and substrates are to be treated to have concentrations/conductivities below those values. Currently there are no industry established values for maintenance painting. Allowable threshold values may be provided by: • State highway agencies • Coating manufacturers (in PDSs) • Major government agencies. If no threshold limits are readily available, the following values can be considered: • Immersion service 3 -.5 µg/cm2 (~24 to 42 µS/cm) for chlorides • Atmospheric service (marine or industrial) 6-10 µg/cm2 (~50 to 83 µS/cm) for chlorides, 6-10 µg/cm2 (~50 to 83 µS/cm) for nitrates and 16-25 µg/cm2 (~133 to 208 µS/cm) for sulfates • Atmospheric service (moderate/mild) 10-30 µg/cm2 (~83 to 250 µS/cm) for chlorides • Atmospheric service (general) 70 µS/cm (Navy) • Immersion service 30 µS/cm (Navy) Figure 14. Use of a Scraper to Remove Loose Paint per SSPC-SP 2

NCHRP Project 14-30 40 Typical soluble salt contamination data may be available from coating assessments and may indicate whether a need exists to perform any type of remediation. The International Standards Organization guidance for maintenance painting recommends checking soluble salt contamination for the first 5 spots repaired and every fifth spot thereafter. If any spot tested is over the specified safe limit, all the spots should be treated to bring the surface contaminants down to an acceptable concentration. For spot painting of small, random repair areas, fewer tests can be performed or soluble salt remediation can be performed in lieu of testing. Remediation is typically performed by pressure washing at 2,500-5,000 psi using narrow fan tips or 0o spinner tips for a more aggressive cleaning action (Figure 15). The best results are obtained when the fan tip is kept close to the target surface (12-18 in.) and the spray gun/wand oriented perpendicular to it. Washing can extend slightly outside the repair area. Bibs or troughs may need to be placed under the washing area to collect the waste water for treatment/disposal. Drip plates may need to be attached to flanges to keep the waste water from flowing away from the collectors. Once the surface has dried sufficiently for the sleeves or patches to adhere, soluble salt measurements can be performed to assess the results of the treatment. If the soluble salt levels are still above the threshold, the area should be re-treated. Testing can be deferred until the power tool cleaning is completed. Another approach is to add a chemical to the washing operation to aid in the removal of soluble salts. Those chemicals contain additives that leave residues on the substrate after cleaning. Coating manufacturers have to approve the use of any of those salt removers with their coatings. For small projects, a water tank, pump, pressure washer, gas tank, hose reel and dosimeter for a salt remover can be housed in the bed of a pick-up truck for convenient soluble salt remediation (Figure 16). Figure 15. Pressure washing with a wand using a 0° Spinner Tip

NCHRP Project 14-30 41 After the soluble salt treatment, the agency may elect to perform soluble salt testing to determine whether the treated surfaces are below the contamination threshold. Testing will use either the sleeve or patch method described above. If the test shows the soluble salt contamination is above the designated threshold, re-treatment and re-testing may be required until the contamination level is below the threshold. Task 4 Power Tool Cleaning — Power tool cleaning is intended to provide a better substrate for paint application than can be obtained by hand tool cleaning. The intent of SSPC SP 3 surface preparation is to only remove loose materials (Figure 17). The existing steel substrate is not to be affected unlike abrasive blasting or the more aggressive power tool cleaning provided by SSPC SP 11 and 15, which are intended to cut profiles in the steel (Figure 18). Figure 16. Pickup truck equipped for pressure washing with salt removers When Washing to Clean and Remediate Soluble Salts Pressure washing is useful for local cleaning of soils and reduction of surface salts in areas to receive spot repairs. If it is performed aggressively using high pressures along with narrow fan or 0o spinner tips, better cleaning and salt remediation will result. Aggressive washing can also cause disbonding of intact existing coating adjacent to the repair area and consequently increase the amount of spot painting work required. Pressure washing of existing lead-based paint may require capture and disposal of the resulting wastewater. There is at least one soluble salt treatment that can be applied with a hand sprayer, brushed on and removed with a light rinsing. It may eliminate the need for capturing and disposing of wastewater. If the initial contamination level is low, the decision may be made to eliminate soluble salt remediation and to rely on dry surface cleaning methods such a burlap wiping. This will typically save a day (at least) in the field painting cycle normally required for washing and drying of the surface prior to power tool cleaning.

NCHRP Project 14-30 42 SSPC-SP 3, “Power Tool Cleaning,” is intended to remove all loose scale, rust, paint and detrimental foreign matter. It is not intended to remove adherent mill scale, rust and paint. The test for adherence is to attempt to lift the substrate with a dull putty knife. Power tools used are: • Rotary or impact power tools to remove stratified rust • Rotary or impact power tools to remove weld slag • Power wire brushing, power abrading, power impact, or other power rotary tools to remove all loose mill scale, all loose or non-adherent rust and all loose paint. The prepared surfaces are not to be burnished (a potential problem with wire brushing). The surface preparation should not form burrs, sharp edges, and sharp cuts. The edges of the remaining existing paint should be feathered to promote the appearance and proper application of the repair coating(s). One recommendation is to remove splinters, weld spatter and other sharp surface flaws. SSPC-SP 11, “Bare Metal Power Tool Cleaning,” is intended to provide a bare metal surface having a 1-mil (minimum) surface profile. Power tools used are: • Grinding tools using bonded abrasive media to cut through corroded surfaces • Impact tools use media to collide with the target surface Grinding tools include reciprocating sanders, orbital sanders or any grinding device using abrasive cloths, discs, wheels or flaps. Impact tools include any rotary or reciprocating tool that uses repeated impacts for generating surfaces including flappers, cutter bundles, needle guns, wire bristle impact and hammer flails. Selection of appropriate tools depends on the condition of the existing surface, the extent of cleaning required, and the surface profile required. Some coatings may require surface profiles produced by specific types of power tools (e.g. bristle blasters).Tool manufacturers can provide recommendations on appropriate tools. Power tools should produce enough power to operate efficiently. Operator fatigue should be considered in selecting them. Figure 17. SP 3 Surface preparation inspected using the SSPC VIS 3 standard Figure 18. SP 11 surface preparation. Note the profile in the exposed steel

NCHRP Project 14-30 43 SP 11 surface preparation initially uses grinding tools for surface cleaning followed by impact tools to create profiles though they may also remove mill scale or be used for irregular surfaces that can’t be completely accessed by grinding tools (e.g. needle gun cleaning of fasteners). Grinding tools are inadequate for generating minimum 1-mil (25 micron) profiles. Grinding tools can remove surface rust to avoid embedding it in the steel using impact tools. Aggressive cleaning with impact tools can create burrs and gouges, with rotary tools it can create burnished surface or damage the surface profile. SSPC-SP 15, “Commercial Power Tool Cleaning,” is similar to SP 11, but 33% (maximum) staining is allowed in every 9 in2 (58 cm2) area. Power Tool Types There are four basic forms of power tools used for surface preparation: • Reciprocating sanders • Rotary or impact tools (rotary flappers, scarifiers, and bristle blasters) • Grinders/sanders • Reciprocating impact tools (chippers, needle guns and scabblers). Pneumatic chippers or scabblers can be used for removing stratified or pack rust (Figure 19). Surface profiling tools include rotary impact flap assemblies (flappers) and needle guns equipped with 2 mm diameter needles which can also be used along with the newer bristle blasters. Needle guns work well in tight places (corners) and on irregular surfaces. Under SP 3 cleaning, a variety of power tools are identified as being suitable for power tool cleaning (e.g., grinders/sanders, needle guns, and rotary impact tools). Grinders have good productivity on flat surfaces where SP 3 surface preparation is sufficient (Figure 20). For areas inaccessible to large rotary impact tools or grinders, needle guns, scalers, and bristle blasters can be used (Figure 21). Rotary impact tools have 5-7 times the productivity of needle guns (Figure 22). Figure 19. Pneumatic chipper used to remove stratified/pack rust Figure 20. Pneumatic grinder equipped with a non-woven pad

NCHRP Project 14-30 44 Impact or rotary impact tools generate the lowest levels of airborne contaminants, which is important when leaded coatings are involved. Many of those tools have custom cleaning media/bits or come in a variety of sizes that can accommodate various surface preparation requirements. Power Sources Power tools can be electric (110 VAC) or pneumatic (at 90 psi). Electric powered tools can be obtained at 115 to 230 VAC from about 1.5 to 10 amps. Battery powered grinders are available that can be fitted with vacuum shrouds for very small work areas. Electric power tools usually have a short duty cycle (e.g., 30 minutes for a needle gun). This limits their utility on projects where large repair areas are encountered. Pneumatic tools require the use of a compressor, typically equipped with a water separator. Reciprocating tools require the least amount of air while larger sanders or rotary scarifiers need more air. Tools typically require about 10 cfm at about 90 psi. Several workers can be accommodated by a towed compressor by attaching a manifold to the compressor discharge. Typical hoses (3/8 in. or 9 mm) can be run 200 feet (61 m) with about 10% pressure loss at 10 CFM (0.28 CMM). In most cases, pneumatic tools are more practical for mechanical surface preparation as they typically have 100% duty cycles, some requiring only periodic oiling. The compressed air should be tested daily per ASTM D4285 “Standard Method for Indicating Oil or Water in Compressed Air” (i.e. the “Blotter Test”). Some power tools requiring daily oiling may exhaust oil on the working surfaces. Those should be periodically tested using ASTM F22. Vacuum Shrouds and Vacuum Systems The intent of the SP 3 surface preparation is primarily to remove loose material or poorly adhered material. If the existing coating is leaded paint, vacuum-shrouded power tools should be used. Vacuum shrouded power tools are also desirable for use with other existing coatings that do not contain lead to collect wastes and limit airborne debris. The shroud surrounds the work piece/media of the power tool. Shrouds can be obtained that conform to specific cleaning requirements (i.e. corners and edges). The shroud confines fine debris generated by the cleaning operation, letting the vacuum extract it. The method of obtaining a seal between the tool and the surface of a work piece varies by tool type. In some instances, it uses a hard shroud and in others, Figure 21. Vacuum shrouded needle gun used for SP 3 surface preparation Figure 22. Rotary flapper impact tool used for SP 3 surface preparation

NCHRP Project 14-30 45 it is a brush head assembly that allows some latitude in conforming the shroud to the work piece and thereby preventing leakage of airborne debris. The efficiency of dust collection depends upon the proper placement of the tool/shroud on the surface being cleaned. The seal of the shroud works best on flat surfaces. The ability to clean complex shapes is limited because of the restrictions of the vacuum shroud. Use of vacuum shrouds on power tools will not significantly affect their production rates. Vacuum-shrouded power tools are specialized equipment and come with the vacuum shroud attached to the tool (Figure 23). A collection/disposal container is needed and is part of the system. The shroud assembly is attached to a vacuum line that transfers the debris generated back to a waste container. A variety of vacuum systems can be used in the field. They range from small 3-6 gallon (11.4-22.7 L) backpack units to 6-55 gallon (22.7-208.2 L) freestanding units (Figure 24). The smaller units usually have 1 to 3 vacuum ports while the larger units have up to 8 ports. Some freestanding units can provide vacuum for power tools 200 ft. (61 m) distant. Some of the smaller units can be pneumatically powered. Air requirements for pneumatic vacuums range from about 50-200 CFM (1.4-5.6 CMM) per tool. Electric units can run on 115 or 230 VAC depending upon size. Regardless of size, vacuums should possess a high efficiency particulate filter (HEPA) so exhaust air meets OSHA requirements. Durability of Cleaning Media Many of those power tools have consumable cleaning media pads, flaps, discs and needles that require frequent replacement. A supply of replacement media and work pieces of the different sizes/types is needed. It has been reported that non-woven textured discs typically last about 5 hours and rotary flappers last approximately 40 hours. Productivity of Power Tools Power tools have different cleaning characteristics and are suitable for cleaning different details (e.g., flatwork, corners, and bolts/rivet heads). Supervisors must provide workers with the appropriate tools and workers must know how to use them properly. Figure 23. Vacuum shrouded grinder and vacuum (on right) Figure 24. Shrouded grinder with back pack vacuum (pneumatic powered)

NCHRP Project 14-30 46 As SP 3 cleaning is only intended to remove loose material, compared to cutting a profile in the steel substrate, the production rate is higher for SP 3 — about 100 ft2/hour (9.29 m2/hour) compared to about 50 ft2/hour (4.64 m2/hour) for SP 15 cleaning and 25 ft2/hour (2.32 m2/hour) for SP 11 cleaning. The cleaning rates also depend upon the type of tool used and the details being cleaned (e.g. flatwork v. bolts/rivet heads). Worker inexperience or lack of training using power tools can also have a significant impact and result in production rates as low as 5-20 ft2/hour (0.46-1.85 m2/hour). Testing indicated that workers using an 8-lb. (3.63 kg) power tool can clean for about 6 hours of an 8-hour day. An increase of 1 lb. (0.45 kg) in tool weight decreases their ability to work to about 4 hours. Feathering Existing Coatings The SSPC power tool standards require feathering of the boundary between the prepared area and the existing coating. Mechanical surface preparation is usually applied about 1-2 inches (2.54- 5.08 cm) beyond the boundary of the failed area into the intact existing paint (2 inches is specified by SSPC PA 1). Feathering can be done by hand using sandpaper or by power tools (grinders) with sanding discs or non-woven pads (Figure 25). Feathered edges are sometimes prone to lifting when coated, requiring a repair. The soundness of the feathered edge is tested by probing around the periphery of the repair area with a dull scraper. Using SSPC-VIS 3 for Inspections SSPC has prepared a visual standard, SSPC-VIS 3, “Guide and Reference Photographs for Steel Surface Prepared by Power and Hand Tool Cleaning,” to assist in the inspection and evaluation of surface preparation methods including hand- and power-tool cleaned substrates. SP 2 and SP 3 substrates are difficult to evaluate as they impact the cleanliness of the prepared surfaces whereas, SP 11 and SP 15 surfaces can be also be evaluated by the profiles created in the steel. VIS 3 provides reference photographs for the four surface preparation standards. The general procedure is as follows: 1. Determine the initial condition of the steel from the reference photographs (conditions A-F) 2. Determine what surface preparation standard is to be met and the appropriate tool (or closely corresponding one) from those provided in VIS 3. 3. Use Table 1 to determine which photographs will depict the result of proper surface preparation based upon 1 and 2. 4. Use the appropriate photographs to compare with surface condition of the fieldwork (e.g., picture GSP3/PWB shows condition G-deteriorated coating over mill scale; SP3 surface preparation; powered wire brush) Figure 25. Feathering of existing coating

NCHRP Project 14-30 47 The visual standards are intended to be used in conjunction with the written standards. Sometimes existing coating conditions and/or power tools vary significantly from VIS 3. In those cases, a field standard can be prepared using a representative area typically 3 ft. x 3 ft. (~1 m x 1 m) containing common surfaces including both flat and complex shapes. The area can receive the specified surface preparation treatment. When agreed upon by all parties, the surface can be painted in lacquer and retained during surface preparation as a field reference standard. In some cases involving SP 3 cleaning, the surfaces have been wiped with white rags and pieces put in baggies for comparisons with wiping tests to be performed after surface preparation. 4.1.4 Monitoring Conditions According to SSPC Standard PA1, “Shop, Field and Maintenance Coating of Metals,” coatings should not be applied when the air and steel temperatures are outside the ranges specified by the coating manufacturer. Most coatings have nearly the same application requirements with respect to relative humidity and dew points (with a few exceptions which can be identified by reviewing PDSs). Safeguards are usually outlined in highway agency standard specifications to prevent coating over surface moisture. There are tolerance limits within each manufacturer’s PDSs to address acceptable application conditions for ambient temperature, relative humidity, and surface temperature. As noted in Section 3.7, coatings should not be applied in rain, wind, snow, fog, or mist, or when the substrate temperature is less than 5° F (2.8° C) above the dew point. Coatings should not be applied on wet or damp surfaces unless so stated in a manufacturer’s PDS. No coating should be applied on frosted or ice-coated surfaces. Coatings can be affected if relative humidity is either too low or too high; those thresholds should be provided by the coating manufacturer. Typically, painting activities should cease when the wind velocity reaches 25 mph (40.2 kph), either in gusts or steady state. The key field measurements are steel surface temperature and dew point. Those measurements need to be taken prior to coating application. The common rule is that painting should not start until the steel temperature is 5° F (2.8° C) above the dew point and rising. Under that condition, moisture from the air will not condense on the steel which would cause problems with coating adhesion. The 5° F (2.8° C) rule provides latitude for accuracies in the measuring devices. Measurements should be taken in the general locations on a bridge where painting operations are to be performed. Once acceptable conditions are present, it is usually advisable to perform follow-up measurements every 4 hours or so. During daytime hours, clouds may obscure the sun, especially if rain is possible. When this occurs, the steel temperature will continue to drop over time, so it is advisable to perform follow-up tests to ensure that acceptable conditions for painting are still present. When painting at night, the steel radiates heat and cools. Periodic tests are necessary, especially at cool temperatures, to know when the steel cools to a temperature within 5o F of the dew point so as to avoid painting over condensation. Generally, the low and high temperatures of concern are 40° F (4.4° C) and 125° F (51.7° C) , respectively (either surface or atmospheric temperatures). The painting crew should consult the PDSs to determine allowable coating, ambient and steel surface temperatures for the coatings being used. Besides relative humidity, some coatings (e.g., moisture-cure polyurethanes) require minimum humidity levels (about 6%) to cure properly, possibly necessitating humidity measurements to ensure that a satisfactory amount of moisture is available. Other coatings may have specified maximum humidity levels. Typically, the maximum relative humidity is 85% though

NCHRP Project 14-30 48 lower limits may be recommended (e.g., 70%). Condensation on freshly painted surfaces can inhibit curing of some types of coatings. For those types of coatings, an up-to-date weather forecast should be obtained prior to paint application if conditions may affect curing (e.g., impending or potential rain, condensation, mist). Surface temperature readings can be obtained using magnetic- based temperature gages, thermocouple/thermistors, or non- contact infrared thermometers. Relative humidity measurements can be obtained using sling psychrometers/tables, or thermal- hygrometers. Inexpensive all-in-one handheld instruments are available to measure air temperature, surface temperature, difference between those temperatures, dew point temperature, and relative humidity. Several types of handheld anemometers are available to measure wind velocity (Figure 26). When performing surface preparation to either SP 11 or SP 15, condition monitoring is recommended to ensure that no condensation forms on the profiled surfaces as they are being created. That could result in rust-back requiring re-work prior to painting. 4.1.5 Coatings Application After completing mechanical surface preparation, the repair areas should be painted as soon as practical (optimally within 24 hours) after final cleaning. Prior to painting, the prepared areas should be visually inspected to ensure they provide suitable substrates to receive the repair coating(s). Surfaces to be painted should be brushed, vacuumed, or blown down with compressed air to remove and dust or loose debris just prior to painting. A maximum allowable period should be established between completion of surface preparation and the application of at least the prime coat if repair area has an exposed metallic surface. Those areas can flash rust if exposed to the atmosphere for few days even in locations sheltered from rain (even Figure 26. All-in-one environmental condition monitor. Note readings placed on adjacent coating. Figure 27. Temporary bulkheads used to isolate areas where different operations are being performed.

NCHRP Project 14-30 49 through a rust patina created by SSPC SP 3 cleaning). In that case, additional power tool cleaning will be required. Any exposed metallic surfaces should be covered if left unpainted due to the onset of inclement weather. Use of a rust inhibitor can be considered to prevent rust-back for several days if painting delays are due to logistical issues or atmospheric conditions. The inhibitor must be certified as compatible with the applied coating by the coating manufacturer. Areas where surface preparation work is being conducted need to be physically separated from areas where paint application is taking place to prevent airborne debris from contaminating the substrate prior to painting or the wet/uncured coating during painting (Figure 27). Coatings may be single or multi-component materials. Manufacturers’ PDSs contain instructions on the proper storage, mixing, and application, which are essential to a successful painting project (e.g., mixing requirements, induction times, and pot lives). Those provide: • Proper surface preparation • Steel surface and ambient conditions • Mixing and thinning instructions • Pot life (if applicable) • Induction time (if applicable) • Film thickness (range) or coverage • Recoat time • Application methods and equipment • Safety (may be in separate manufacturer SDSs) Mixing Paint application begins with mixing/agitation at the mixing site. The mixing site should be located in reasonable proximity to the painting site to minimize transport distance and time to the paint application locations. For solvent-based coatings, the mixing/thinning location should be in an open well-lit area away from any source of ignition. Paint crews typically want to begin painting as early as possible in a work shift. In some cases, the mixing operation can begin before painting conditions are met if the atmosphere is free of mist or rain, unfavorable weather is not imminent, and the dew point is climbing above the surface temperature of the steel. If the coatings have short pot lives at ambient temperatures, mixing should be deferred until painting conditions are met at the bridge. Paint application is addressed by SSPC-PA1, “Shop, Field and Maintenance Coating of Metals.” Hand mixing can be used for single-component coatings. For hand mixing, any skin formed on coating should be removed prior to mixing. The liquid coating (vehicle) in the paint can should be poured into a clean container. Pigments remaining in the can need to be loosened by scraping and thoroughly mixed with the vehicle with a stirring paddle as it is poured back into the original can. Some painters perform hand mixing by “boxing,” repeatedly pouring the coating back and forth in two containers. Boxing is not recommended for moisture-cure polyurethanes as it can result in improper curing. Mixing should continue until the coating composition is uniform in appearance. As a general rule, any skins found on opening coating containers that constitute 2% or more of the weight of the coating should result in the coating being discarded. If pigments in the container have settled and hardened, the coating should be discarded. Power mixing using a suitable mixer with agitator blade can be used on both single- and multi-component coatings. For large projects, fixed units are available for mixing in 5-gallon (18.9 L) containers. Pneumatic and electric hand drills are suitable for mixing small paint quantities, 1- 2 gallons (3.79-7.57 L). Multi-component coatings should be mixed in proper proportions. To prevent incorrect mixing ratios, the coating components should be furnished as pre-measured

NCHRP Project 14-30 50 kits. Dry components may be provided with a coating. They should be mixed in a manner to promote uniform blending with the vehicle. Excessive power mixing or mixing at high speeds can result in high shear forces in coatings with heavy metallic pigments and generate high temperatures within the coating. This is to be avoided. After mixing, the coating should be strained or filtered using a screen size that removes undesirable matter but not the pigment. Catalysts, curing agents, or hardeners that are separately packaged should be added to the base coating after it is thoroughly mixed. For multi-coat applications of the same coating, it is usually desirable to tint one coat so that it can be distinguished from the other. In some cases, the coating may have a metallic appearance similar to a prepared substrate. Tinting of the first coat applied can provide suitable contrast between painted and unpainted surfaces. If one of the coats is to be the topcoat, it should contain no tint. Tinting can be performed by the manufacturer and provided in separate marked containers. Thinning of coatings may be required when a brush or roll application is used. It is more commonly used for spray application. Thinning must be approved by the highway agency or its on-site representative. The type and amount of solvent must be in accordance with a coating manufacturer’s PDSs for prevailing atmospheric conditions and surface temperatures. Local air pollution regulations also impact thinning. For spraying, the paint may need to be thinned for proper application; the spray pump, lines, and gun will be needed to be purged/cleaned daily (for most coatings). Spent solvent must be captured in buckets and disposed of. Some constituents may render spent solvents hazardous wastes. Highway agencies typically have protocols for disposing of that waste stream. The coatings to be used need to be mixed (for two-component coatings) and agitated for a period specified by the manufacturer. Amine epoxy coatings will need to be given a set time (termed induction time) of about 30 minutes after coating to react before application. Most of the two-component coatings have limited pot lives and must be applied before that is expired. Pot lives are usually given at 75° F (23.9° C). A typical epoxy will have a pot life of 2 hours at 75° F (23.9° C). A rule of thumb is that pot lives halve for every 20° F (11.1° C) rise in temperature over the pot life stated for 75° F (23.9° C). At 95° F (35° C) , the same epoxy will have a pot life of just 1 hour. Good planning is required to ensure that only the amount to be used is prepared to minimize waste. Coatings should be transferred to the work area in sealed buckets with the painters using stirring sticks to agitate the coatings just prior to application. Some coatings will need to be re-agitated if they are not used in a short period. Moisture-cure polyurethanes usually do not require re-agitation. Coatings that do not have limited pot lives, or that do not deteriorate on standing, may be placed in covered containers and stored overnight. Coatings Application Rules of thumb for when coating application should not be performed include: • Dusty conditions unless containment is used • Light on the surface is less than 15 ft.-candles (161 Lux) • Ambient temperature is less than 45o F (7.2o C) • Relative humidity exceeds 85 percent • Surface temperature is less than 5o F (2.8o C)above the dew point • Surface temperature exceeds the manufacturer’s recommendation • Ambient temperature exceeds 95o F (35o C), unless the manufacturer allows a higher temperature

NCHRP Project 14-30 51 When no PDS is available or a PDS does not provide detailed application information, those guidelines are generally safe to follow. If questions remain about application issues, the manufacturer’s representative can usually provide the information. In addition, most coatings manufacturers have their PDSs online, making them readily accessible with computer, tablets, or phones. Several problems with common coatings can be encountered in cold weather painting operations. Since most spot painting work is short-term and does not use containment or environmental controls, it should not be performed when most cold weather conditions are encountered, even in anticipation of nighttime freezing conditions. In some cases, the coating manufacturer may require the pre-treatment of an existing substrate prior to application of a coating. That may be in the form of a rust preventative, a solvent wipe, or other pretreatment chemical. In applying multiple coats, successive coatings should be applied before any degradation or contamination can occur. Spot painting typically entails applying coatings to small areas. Application methods include: • Brushes • Rollers • Daubers • Mitts • Sprayers. Brush, roller, dauber, or mitt application methods are simple to use by relatively unskilled workers and have reduced environmental and worker safety impacts compared to spraying. Brushing works best on irregular substrates and for working paint into edges of the existing paint (Figure 28). Brush types are selected based upon the details to be coated. Typically, flat brushes are used for flat surfaces while round brushes are used on irregular surfaces such as bolts and rivets. For flat brushes, a maximum width of 5 inches (12.7 cm) is recommended. Brushes should be able to apply a relatively uniform coat. The coating should be thoroughly worked into all crevices and corners. A good procedure is to brush the coating from the failed area outward over the border and onto the existing coating throughout the repair area. If any of the existing coating is loose at the boundary, this step can work fresh paint into the gaps between the substrate and the existing coating, “locking” it down so that there will be no subsequent disbonding failures in the repair. Care should be taken to properly coat bolts and rivets. All runs or sages should be brushed out immediately. If feathering causes disbonding of the existing coating during or just after paint application, it can be eliminated. After power tool cleaning, the existing blunt edges can be probed back adherent paint with a dull scraper and the abrupt boundary between the prepared surface and the existing coating “locked down” with the repair coatings by brushing them from the prepared surface into the existing coating to ensure penetration of the repair coating into gaps under the existing coating. This method will resist lifting. Rolling is typically used for flat work (Figure 29). It should not be used for coating irregular surfaces such as fasteners. Rolling is faster than brushing, but care needs to be taken not to apply too thin a coating. The appropriate roller nap should be matched to the roughness of the surface being painted and selected based on the recommendation of the coating manufacturer. For painting over previously corroded substrates priming can be performed with stiff brushes with subsequent top coats applied using long nap rollers.

NCHRP Project 14-30 52 Daubers can be used for painting areas with poor access for other application methods. Paint mitts can be used to apply coatings on laced and riveted beams (Figure 30). In applying coatings by these methods, the painters should try to provide smooth uniform continuous films that are in the range of wet film coating thickness specified by the PDSs. Airless sprayers use a pump to push the coating through a small hole in a spray gun that causes the coating to atomize and be uniformly deposited on a surface. Small gasoline/electric powered units may be practical for spot painting projects. Larger pumps can also be used that require an air compressor. The pump sends paint through lines to the spray gun. The connecting hose can be up to several hundred feet long. The gun applies the paint in a uniform fan pattern onto the substrate. The equipment requires more experience and applicator technique than brushing or rolling. Spray nozzle tip (orifice) sizes should be based upon the coating manufacturer’s recommendations, though some preliminary testing may be needed to determine the most appropriate one. For larger repair areas, conventional airless spray equipment can be utilized if suitably skilled personnel and equipment are available. Small areas can be sprayed using the new battery-powered airless spray units (Figure 31). Spray application using conventional equipment is most practical when large spot repairs are to be performed. Depending on the coating being sprayed and the location, containment may be required to prevent overspray damage. Spraying is the best method of applying coatings where high film builds can be achieved in a single application or wet-on-wet. That is difficult to achieve using brushing or rolling. In some cases, involving larger spot repairs, a combination of methods can be employed. The coating can be delivered to an area by spraying. Then, brushing can be used to work it into irregular surfaces and correct any surface defects while the coating is wet. Spraying may be the only practical method for delivering paint to the inside faces of laced and riveted box beams. For work on large repair areas, this may be more efficient than by delivering buckets of coatings to the painters, especially if they are working some distance away from the mixing site. Figure 28. Brush application of finish coat Figure 29. Roller application of an intermediate coat

NCHRP Project 14-30 53 Wet and Dry Film Thickness Measurements An important factor in coating quality is obtaining proper cured film thickness — dry film thickness (DFT). When the applied coating is still wet, painters can use a tooth/step gage to measure the wet film thickness. The gage gives the wet film thickness in mils (1 mil =.001”) or microns (1 micron =.00025”). The anticipated DFT is given by the formula: Dry Film Thickness = Wet Film Thickness x Percent Solids in the Coating The percent of solids in a coating is typically provided by a coating manufacturer in the PDSs. If a coating is thinned, the estimated dry film thickness is reduced further based upon wet film measurements. The anticipated DFT is given by the formula: Dry Film Thickness = Wet Film Thickness x Percent Solids in the Coating / (1 + Percentage of Thinner Added by Volume) Paint manufacturers usually specify coating thicknesses (both wet and dry film) in terms of acceptable upper and lower bounds. If the wet film thickness is too low, painters can add another wet application before the initial application hardens. If the wet film is excessive, painters can reduce it by spreading it further with a brush or roller. In applying spot coatings, painters need to provide a uniform film build and avoid drips or misses. A tooth gage should be used to measure wet film thickness in accordance with ASTM D1212, “Standard Test Methods for Measurement of Wet Film Thickness of Organic Coatings” — Method A (Figure 36). Some coatings remain soft for weeks making follow-up DFT measurements hard to perform with standard tests. In that case, the painters can leave a few WFT impressions in the coating for the inspector/supervisor to read ensuring that the proper WFT build is achieved and that the DFT thickness will be correct. Recoat Windows and Other Topcoating Delays For multiple-coat systems, there is usually a minimum recoat time (termed “recoat window”) before applying a topcoat. That time depends upon the ambient temperature, the surface Figure 30. Coating application on riveted steel using a mitt Figure 31 Spot coating application using a battery powered sprayer

NCHRP Project 14-30 54 temperature of the bridge steel, and for some coatings relative humidity. Some coatings have a recoat window consisting of minimum and maximum recoat times. If the maximum recoat time is exceeded, the coating must be abraded with fine sand paper or painted with a tie coating to achieve an acceptable bond with the top coat. Caltrans uses a low-pressure rinse process for treating applied coatings if they are to be topcoated and there is a delay beyond 72 hours. The specified rinse uses a low-pressure potable water spray at 1,160 psi (80 bar) applied with the nozzle tip 12-18 inches (30.5- 45.7 cm) from the work piece using a 45° fan tip. The PDS will have the recommended coating thickness (typically minimum and maximum WFTs and DFTs). On rough or severely pitted surfaces, it may be difficult to measure coating thickness. In those cases, painters should take care to achieve a continuous film build and fix pinholes. Proper film build is usually difficult to achieve using coatings intended to be applied at thin film builds. When insufficient coating thickness is applied, the substrate may be visible through the coating. A thin coating may be brittle and crack. Excessive film thicknesses can result in coating problems including blistering, solvent entrapment and disbonding (Figure 33). Greater film thicknesses also delay coating cure times. Stripe Coating While time on a bridge is generally limited for spot painting, many times spot repairs are affected where the original paint application was inadequate. If such problems have been observed, it might be beneficial to apply extra paint in problematic locations to ensure they are properly coated. Stripe coating can be performed per SSPC PA 11, “Protecting Edges, Crevices, and Irregular Surfaces by Stripe Coating” (Figure 34). Areas that are usually stripe coated include: • Crevices • Plate and sharp edges • Plate seams • Back-to-back angle seams (built up members) • Pitted steel • Bolt heads and nuts • Rivet heads • Welds • Other sharp discontinuities • Outside corners Figure 32. Painter measuring wet film thickness using a tooth gage

NCHRP Project 14-30 55 SSPC-PA 1, “Shop, Field, and Maintenance Coating of Metals,” recommends brushing for applying stripe coats as it works the paint into the pores and crevices and allows the greatest control over the boundaries of the striped areas. Rolling can be used where striping involves coating simple shapes such as edges of girder flanges. One drawback with stripe coating is that it adds another step to the coating process and requires additional dry time for the spot coating to cure. The decision to stripe needs to be balanced with the requirements for other painting tasks and the work time allotted for the project. Quality Control Actions during Painting During and just after the coating application process, painters can perform quality control actions that limit the need for time consuming repairs. While coatings are still wet, painters have the opportunity correct minor flaws, typically by brushing, which becomes difficult to repair once a coating has dried. Sags and runs, whether appearing during brushing, rolling, or spraying, can be brushed out. Painters can inspect the wet film to detect bubbles or other signs of pin-holing and dab those spots with a brush to eliminate them. Inspection will typically reveal lifting that occurs at the boundary areas between the spot repair and the existing coating, generally where the latter was feathered. In those cases, the lifted paint (and wet paint covering it) can be removed with a scraper and touched up by brushing fresh coating in the area. Close inspection by painters can also reveal missed and thin areas that can be repaired by applying additional coating. If several repair coatings are applied, the top coat is usually intended to protect underlying coats from UV degradation. The top coat should be the only repair coat visible when viewing the spot repair. If underlying coats extend beyond the top coat, they should be covered with the top coat. When applying spot coatings on hand- and power-tool cleaned areas, the finish coat can conform to the repair area (Figure 35) or, if visible to the public (e.g., fascia girders of grade separation bridges) it can be squared up to provide a better appearance (Figure 36). Figure 33. Blistering of polyurethane top coat due to excessive thickness Figure 34. Stripe coating the edge of a cross-frame using a roller

NCHRP Project 14-30 56 Inspection of Work and Affecting Repairs Once the spot coating has been applied, a final inspection can be performed of all repair areas to ensure that the work has been properly performed. For spot painting work, this includes: • Confirming that the damaged areas were completely repaired (and for the bridge that all repair locations were spot painted) • Inspecting the coated areas for signs of coating distress, improper cleaning, or pick- up of soils • Inspecting the bridge for any damage to the existing coating due to access issues • Measuring the dry film thickness of the repair areas. • Performing any necessary repairs. Ideally, the crew should use hold points for inspections. Once each task is completed at a location, the supervisor can inspect a repair location and either require re-work or accept it, allowing the crew to proceed with the next task. Unfortunately, demands upon a supervisor may only permit inspection once the work is complete. Under that constraint, it is best that the inspection take place while the crew is still at the jobsite, and preferably while they are still working in the general area of the completed spot painting work being inspected. This allows for prompt repairs, if necessary, and expedites the final inspection process. It also permits the detection of any consistent application problems, such as failures to paint the back faces of bolts. The supervisor can emphasize such shortcomings to the painters to prevent reoccurrences as they work through the bridge. A properly applied spot painting repair should provide a continuous coating over a failed area and the repair extending several inches past the feathered edge into the existing coating with only the top coat evident over the existing coating. The repair coating should be free of obvious defects including blisters/bubbling, blushing, embedded debris, holidays/misses, lifting, mud cracking, orange peel, pinholes, pitting, wrinkling, or sags/runs. A useful tool is an inspection mirror that can be used to inspect areas that cannot be viewed directly (Figure 37). It would be useful to provide workers with mirrors so they can inspect their work and make needed touch-ups while painting. In addition to inspecting spot repairs, the supervisor should look for damage to the existing coating caused aerial lifts, cables, or attachment brackets. Such locations need to be Figure 35. Spot coating conforming to the repair area Figure 36. Spot coating with squared-up finish coat

NCHRP Project 14-30 57 repaired like the spot painting work. The coating/coating system should also have sufficient build (thickness) within limits specified by the coating manufacturer. The supervisor can measure the DFT of each coat of paint or measure the total DFT build in the repair areas. Measuring DFTs on bridge components can be performed using SSPC PA 2, “Procedure for Determining Conformance to Dry Coating Thickness Requirements.” Testing is to be performed using nondestructive coating thickness gages (Type 1 magnetic pull-off and Type 2 eddy current) per ASTM D7091, “Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic Nonconductive Coatings Applied to Non-Ferrous Metals.” The supervisor should be provided either a Type 1 gage, along with thickness standards, or Type 2 gage along with plastic shims incorporating the range of coating thicknesses anticipated. The use of Type 2 gages is recommended due to their ability to take quick measurements and be calibrated using a variety of substrates (Figure 38). The Type 2 gage can be calibrated using one or two shims over the power tool-cleaned substrate. Generally, those types of gages are difficult to use where coatings have been applied over irregular surfaces typical of severe corrosion damage. The approach used in SSPC PA 2 is to take 3 thickness readings in a narrow 1.5 in.(38 cm) diameter circle and take an average of the values (discarding significant outliers). The minimum acceptable thickness for spot measurements is 80% of an average reading while the maximum acceptable coating thickness may be up to 150% of the specified maximum thickness for Coating Thickness Restriction Level 4 in Table 1 of SSPC PA 2 (or an unrestricted maximum thickness for Level 5). This may work well for large spot painting projects incorporating abrasive blasting and spray application. However, for brush, roll, and mitt applications on smaller areas prepared by SSPC SP 2 or SP 3, those limits may be impractically tight. If a supervisor inspects work after the paint crew has moved to a different site on the bridge, they can mark the areas requiring repair so subsequent corrections can be made (Figure 39). Five spot readings, each an average of 3 consistent readings within a 1.5 in. (38 cm) diameter), should be taken approximately every 100 ft2 (9.29 m2). For smaller spot painting repair areas, fewer readings are needed per location, but more locations probably need to be measured. Appendix 1 of SSPC PA 2 provides an example for taking measurements in a non-conforming area of about 30 ft2 wherein 5 readings are taken. For small repair areas measuring 3 ft. x 3 ft. or less, one or two readings may suffice. Appendix 2 of SSPC PA 2 provides guidance for taking Figure 37. Inspection mirror used to detect lack of coating on backside of fastener Figure 38. Typical coating dry film thickness measuring instruments

NCHRP Project 14-30 58 measurements on steel beams. Even for relatively small areas of a few square feet, it recommended that the reading be taken on spot repairs in both the flanges and webs if necessary. When damaged coatings, thin coatings or missed areas are detected, the coating in the area should be completely removed and a spot repair should be performed and re-inspected prior to final approval (Figure 40). 4.1.5 Demobilization Once the painting work is completed, inspected, and approved, the crew should conduct a thorough clean- up of the jobsite. If spot painting involved existing lead-based paint, ground cloths, and windscreens should be vacuumed to remove any lead paint residues before being taken off-site. All respirator filters, disposable clothing, vacuum filters, and other disposable items that could be contaminated with lead should be placed in appropriate containers for miscellaneous hazards waste and properly disposed. All hazardous materials should be removed and either taken to an agency’s facility (with permission of the DNR) or manifested and disposed of if wasted. All work-related trash should be collected, and the area inspected for loose paint chips which were not previously collected. If those contain lead, they should be disposed of in a hazardous waste container. If lead-based coatings were disturbed during spot painting, the agency may elect to perform pre- and post-work soil testing or other tests of water and sediment to confirm that the work did not result in lead contamination (Figure 41). A final inspection should be performed to ascertain that a proper clean-up was achieved. The equipment and surplus paint not opened or damaged during the project should be returned to the agency shop. Paint can be stored for future use on other projects. The agency may elect to mark the final date of spot painting work on beam ends to assist in tracking paint work on the bridge. Figure 39. Marked painted area for follow-up corrective work by painters Figure 40. Painter repairing a coating defect Figure 41. Worker taking a soil sample after a project is complete

Next: Chapter 5.0 Worker Safety and Compliance with Environmental Regulations »
Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance Get This Book
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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 251: Spot Painting to Extend Highway Bridge Coating Life: Volume 1: Guidance provides approaches for employing spot painting in a cost-effective, safe, and environmentally compliant manner. Bridge coatings are the primary means of corrosion protection for steel bridges in the United States. Most bridge coatings tend to fail prematurely in localized areas and spot painting can be used restore the lost corrosion protection and extend the service lives of existing bridge coatings, often at a fraction of the cost of a complete bridge repainting. However, many state highway agencies do not perform spot painting primarily due to performance concerns and lack of familiarity with its proper utilization and execution.

The guidance is accompanied by NCHRP Web-Only Document 251: Volume 2: Research Overview provides the evaluation method for the guidance document.

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