Conservation of Historic Stone Buildings and Monuments (1982) / Chapter Skim
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Diagnosis of Nonstructural Problems in Historic Masonry
Diagnosis of Nonstructural Problems in Historic Masonry
Pages 211-232
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From page 211... ...
For inst~nce, frequent problems occur from the corrosion of metal anchorage devices, improper design of stone details precluding proper drainage of rainwater, and the unexpected ramifications of newly installed air conditioning or the introduction of thermal insulation. A variety of cases are identified to aid in the proper diagnosis of problems and determination of treatments.
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From page 212... ...
Thus, after presenting some overriding conditions, the following building elements are discussed: · Walls · Top of Walls · Window Openings · Base of Walls In each case, emphasis is placed on an evaluation of actual building practices to determine causes for common problems. Proper identification and understanding of the earlier building systems is indispensable when attempting to diagnose current problems and prescribe treatments.
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From page 213... ...
Unfortunately, this point was often ignored, so we are now faced with treating severe deterioration of stone or brick that has little hope of lasting very far into the future. Third, there are many cases of chemical and physical incompatibilities among building materials.
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From page 214... ...
This is one of the most interesting evolutions in terms of changing technologies, introduction of new building materials, adaption of traditional designs, and new engineering approaches. Bearing Walls To diagnose problems in masonry bearing wails properly one must understand the typical building practices employed.
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From page 215... ...
This comb- result in a failure or collapse of the stonework affected. It is now known that wrought iron, cast iron, or steel anchors set in sulfur or in mortar can become severely corroded if moisture reacts with the sulfur (forming sulfuric acid)
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From page 216... ...
The metal ties were first made of wrought and cast iron; then, by the mid-nineteenth century, galvanized iron, painted iron, iron dipped in tar, and even copper or bronze were used. Early literature shows that some of these cavity-wall ties were shaped to reduce corrosion problems by eliminating flat surfaces (potential catch basins for moisture in the cavity)
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From page 217... ...
Therefore, through time these metal ties have often failed because of corrosion, which results in a loss of the wall's structural integrity. Cavity-wall construction can be identified through physical probing, which involves careful core drilling or discreet dismantling of a portion of a wall, or with various nondestructive techniques.
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From page 218... ...
Strength was not an issue. Incus, sanguine bricks, architectural terra-cotta, cast stone, glass, metal sandwich panels, and so forth were ah substitutes for traditional masonry.
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From page 219... ...
, and then the inner masonry backup material resulting in a total wall thickness of about 12 in. With this type of wall, new details had to be devised to sheath the structural iron with masonry.
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From page 221... ...
In a bearing wall, the mortar joint is strictly in compression, and the expansion or contraction of materials has little effect on the structural integrity of the wall. With the evolution of the curtain wall, builders changed to a stronger, waterproof, Portland cement mortar, usually a mixture of
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From page 222... ...
Left unattended, such deterioration could result in severe damage to individual building elements or, in extreme cases, in a failure of a structural component. To counter these potential problems, modem high-rise buildings rely heavily on flexible joint sealants.
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From page 223... ...
Now, expansion joints are recommended every 20 linear feet. Cornices and Overhangs In a building of simple bearing-wall construction, a stone cornice would merely be corbelled or cantilevered out beyond the stone below.
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From page 224... ...
The bolt heads and nuts under the soffit are exposed to the weather, and other steel angles are very close to the surface of the stone (at points a and b, and susceptible to corrosion. Finally, composition roofing rarely lasts it, id.., .., ..
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From page 225... ...
This type of gutter must be periodically inspected to assure that leaves or debris do not block proper drainage.
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From page 226... ...
This cornice design directs rainwater toward the roof and a central water control system. The design requires extensive flashing, which is especially subject to corrosion and damage to the surface.
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From page 227... ...
34. WINDOW OPENINGS IN MASONRY Sills A common location for masonry deterioration or darnage is at window (and door)
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From page 228... ...
Little provision is made for rainwater coming down the face FIGURE 12 Staining from "slip" sills. Water flowing off the sill invariably stains the wall and seriously erodes mortar joints in the dam age area j shown with cross hatching!
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From page 229... ...
For instance, outside surfaces of foundation wads were often coated with cement pargeting or asphaltic mastics. Through the years, these coatings become dislodged and no longer block moisture penetration.
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From page 230... ...
One in particular is the repair of deteriorated mortar joints in masonry curtain walls. In attempting to reestablish a waterproof joint, should traditional "tuck pointing" techniques with a waterproof mortar be used, or should the joints be wiped with a "slurry coat" {a near-liquid cement mixture)
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From page 231... ...
· Study of cost-effective and practical ways to apply thermal insulation to masonry walls in early twentieth century buildings must be undertaken. Problems of moisture migration through the wails, increased potential of freeze/thaw problems with masonry, and the aesthetic considerations of adding insulation to interior or exterior wad surfaces should be thoroughly studied.
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From page 232... ...
4-5. The preservation of building stone, The American Architect and Building News.
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