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NCHRP Project 14-30 1 1.0 OVERVIEW There are about 170,000 steel bridges in the U.S. that rely on protective coatings for corrosion protection. Maintaining that protection is a major expense and concern of transportation agencies, many of which are struggling to address a variety of bridge and roadway maintenance shortfalls. A major challenge of those agencies is to keep the nationâs bridges in a state of good repair, often with limited budgets. Spot painting is an important tool for those agencies to use to extend the service lives of existing bridge coatings and enable transportation agencies to get the maximum value from limited funds. Spot painting is one of four maintenance painting options along with zone painting, overcoating, and coating removal and replacement. The four maintenance painting options are most effective when used in applying the appropriate bridge preservation treatments and activities at the appropriate time (and to the appropriate bridge). Deterioration of coatings is generally promoted by environmental exposure conditions that provide UV radiation from sunlight, moisture and oxygen, and for bridges soluble salts from deicing chemicals and aggressive environments such as marine and severe industrial exposures. Spot painting may be used under certain conditions to restore corrosion protection and extend bridge component life at a minimum cost. The primary goal of this guide is to be a useful resource tool for in house maintenance personnel charged with employing proper utilization of spot painting techniques and materials on steel bridges. Objectives include describing and explaining the what, why, and how of spot painting as determined by best practices. Attention will be given to: 1) assessment of existing bridge coatings to select the appropriate maintenance painting option; 2) coating selection; 3) preparation (bridge site and steel substrates) and coating application (and repair); and 5) coating inspection and demobilization. In addition, worker safety and environmental factors will be reviewed. The following depicts the step-by-step activity flow for spot painting: A particular concern of this guide is coating selection for spot coating which is important and affects the long-term success of projects. The selection affects: 1) the existing coatings to be repaired/replaced, 2) worker safety procedures used by field personnel, 3) surface preparation, 4) environmental protection requirements, 5) atmospheric conditions for application, 6) application Bridge steel is painted primarily to resist corrosion. A protective coatingâs ability to protect steel is based upon its integrity and inherent capability to handle the external stresses that cause it to deteriorate and the steel to corrode. Properly applied coatings offer maximum corrosion protection. Any faults in the coating will short-circuit its protection and lead to premature corrosion of the steel. More aggressive environments challenge the ability of coatings to remain protective and the steel to resist corrosion, which can nucleate, spread and undermine a coatings ability to protect.
NCHRP Project 14-30 2 methods, and 7) durability of a repair. As there is typically interaction between coating repairs and repair coatings, a range of issues need to be considered related to both the demands on the maintenance coating and the characteristics of the existing coating. Factors to consider when selecting coatings for spot painting coatings are: 1) compatibility and durability matching with existing coating, 2) chloride contamination, 3) application in severe environments/conditions, 4) surface tolerance, 5) special application requirements, and 6) user (painter) friendliness. Typical generic common bridge coating types are discussed including: ⢠Acrylics (Waterborne) ⢠Alkyds ⢠Epoxies ⢠Polyurethanes Coatings are employed as single coats or in multi-coat paint systems for maintenance painting options, including spot painting. Those are discussed in terms of coatings used over profiled steel and marginally prepared substrates. Factors impacting coating selection are addressed including soluble salt surface contaminants, volatile organic compound (solvent) restrictions, and spot coating characteristics (including user friendliness). Non-traditional coatings including tapes, greases, and conversion coatings are also addressed. Performing spot painting effectively depends upon proper scoping of the project addressing operational, environmental and worker safety requirements and assembling all equipment and supplies necessary for the fieldwork during mobilization. Deployment actions at the job site accommodate support actions for effective spot painting work while complying with environmental and working safety requirements. Timely inspections through the use of hold points at key junctures in the painting work promotes quality spot painting work and maximum project durability. Surface preparation work emphasizes power tool cleaning as it is typically more practical to implement by highway agencies for spot painting than other methods. Observance of ambient paint conditions is a necessary precursor to paint application. Adherence to coating application procedures results in properly applied coatings and minimum requirements for repair. Spot painting requires attention to a range of issues related to compliance with worker safety and environmental regulations. Key worker safety requirements relate to training, hazard communication, use of personal protective equipment (PPE), worker hygiene, medical surveillance and testing (for existing lead coatings) and reporting/recordkeeping. Environmental compliance relates to protection of the public, workers and the environment from wastes generated during maintenance painting operations. Those wastes can be wastewater from washing operations along with airborne particulates and solid wastes from surface preparation operations. Those are contained and captured by troughs, vacuum shrouded power tools, along with ground cloths and containments. The captured wastes must be collected, stored and disposed of properly with special permitting, storage and disposal requirements for hazardous wastes. Waste coatings and solvents commonly employed for spot painting require collection and disposal. Knowledge of and proper attention to those requirements is vital to ensure regulatory compliance. This guide is organized to adequately cover the activities needed for successful spot painting: Section 2 briefly describes maintenance painting options and the assessment of existing
NCHRP Project 14-30 3 coatings on bridges. Appendices A-C are provided for: instructions for performing field assessments, a sample state highway agency coating assessment form, and recommended equipment for performing field assessments. Section 3 provides guidance on the vital topic of spot coating(s) including their uses, performance characteristics, and user friendliness. Section 4 explains the technical issues and best practices for: ⢠Preparation of work sites ⢠Surface preparation (steel substrates) ⢠Coatings application and inspection Appendix D is provided with a list of proposed equipment for performing spot painting in the field. Section 5 addresses worker safety and compliance with environmental regulations To facilitate use of this guide, the references for each chapter have been appended to Appendix E and are available for persons wishing to further investigate the practice of spot painting.
