MASONRY REPLACEMENT AND SEALANTS
If brick is missing or requires replacement every effort should be made to match the original brick in size, color and texture. This can be accomplished by seeking out salvage companies which have a stock of historic bricks retrieved from razed structures. Brick can often be located which matches the original in most respects. In extreme cases if only a few bricks are required it may be acceptable to remove original bricks from a rear facade for replacement on side or main facades. The rear facade can then be patched with bricks which match as closely as possible. It is generally more difficult to match old brick with modern manufactured bricks but this should also be explored for brick replacement.
Sealants on brick and masonry surfaces are not recommended. They have a limited life span and in general have not been found to have a long-term preserving effect. Water repellents and waterproof coatings should only be used in extreme cases of damage, such as on sandblasted bricks which have become so porous that paint or some type of coating is essential. If a problem occurs on only a portion of the masonry, it usually is best to treat only the problem area rather than the entire building.
- Waterproof coatings -- Waterproof coatings seal the surface from liquid water and from water vapor; they usually are opaque, such as bituminous coatings and some paints. If water does enter the wall the coating can intensify the damage because the water will not be able to escape. In cold weather the water in the wall can freeze, causing serious mechanical disruption, such as spalling. Additionally, the water will follow the path of least resistance, and can result in damage to interior surfaces.
- Water repellent coatings -- Water repellents keep liquid water from penetrating the surface but allow water vapor to enter and leave the surface through the "pores" of the masonry. They usually are transparent, such as the silicone coatings, although they may change the reflective property of the masonry. As water repellent coatings do not seal the surface to water vapor, it can condense inside the wall at cold spots, producing liquid water, and result in the same adverse effects as described above. Additionally, damage can be done by soluble salts. Salts frequently are present in the masonry and liquid water can dissolve these salts and carry them toward the surface. The water repellent coating prevents the water and dissolved salts from coming completely to the surface and the salts are then deposited slightly below the surface. Over time these salt crystals will grow and develop substantial pressures which will spall the masonry.
- Stucco and Concrete -- The use of stucco and concrete as sealants is not permitted. In addition to altering the appearance of a structure stucco and concrete can also damage the underlying brick or masonry surface through its bonding process.
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