Brick deterioration
Bricks come in many shapes, sizes, and materials. Fired bricks are some of the longest lasting masonry material types, but they do require maintenance, or they can face a series of deterioration issues. Most brick deterioration occurs due to moisture. Before repairs can be completed, the source of moisture needs to be repaired, otherwise failure will continue to happen. The most common brick deterioration issues are:
Spalling
When water does not shed from brick surfaces or gets into mortar cracks and then goes through a freeze/thaw cycle, the water can expand one-eleventh of its volume. This expansion causes further cracking. If this happens on the face of a brick it causes large amounts of the face to crack and break off and is known as spalling. It is almost always accompanied by loose, missing, or cracked mortar. If spalling is found, it means that moisture is inside the brick and mortar and has the potential to seep into surrounding bricks. When found, repair work should be done immediately to prevent spalling from spreading. The repair usually consists of replacing damaged brick and repointing. Repointing will be addressed later.[1]
Buckling
Buckling happens when the mortar has fallen or washed away. When this happens, the bricks are no longer held into place. They begin to collapse on themselves or completely off the wall. If moisture is behind the bricks and the front-most mortar is still in place, buckling can be seen in what appears to be bubbling—a section of brick that bubbles out from the rest of the wall. When buckling occurs, address the moisture problem, then if the bricks are undamaged, repoint the mortar and set or replace the brick.
Rising damp
Bricks, which are porous, draw ground moisture upward through capillary action and result in rising damp. The rising of moisture can affect many layers of brick depending on brick hardness and how humid the area is. Humidity may prevent the bricks from fully drying out, which will allow the capillary action to continue. Continued exposure to moisture—sprinkler systems—can cause a similar effect.[2] Rising damp manifests by the washing away of brick, often turning the brick into piles of clay/sand dust.
Exfoliation
Exfoliation happens when the surface has been abrasively cleaned (sandblast, iceblast, beadblasting, etc.) or repeatedly exposed to moisture, salts, and rubbing pressure. This can be recognized by the coarse surface with undefined edges or features. The brick is often set back into the mortar and rounded or curved. This is dangerous for bricks because once the face—the hardest surface of a brick—gets removed, through one of the methods above, it become susceptible to absorbing moisture causing total brick failure. Other than brick replacement, there is no repair for exfoliation. However, preventative maintenance can prevent exfoliation from happening. Proper moisture removal such as removing snow, and installing rain gutters, downspouts, and drains will allow the moisture to move away from the brick.[3]
Efflorescence
Efflorescence can be seen usually as a white or tan powder or crystal on the brick face. Moisture gets pulled into the brick and as the water evaporates, the minerals found in the water, mostly salt, are left behind. Through the least abrasive method of scrubbing the brick, the efflorescence can be washed away. The efflorescence in itself is not damaging. The damage is caused by water getting into the brick. The source of water must be addressed before the bricks develop damaging issues.[4]
Step cracking
A crack that usually follows mortar lines moving up/down and over is known as step cracking. This can appear in one step-line, which is caused by settling. The brick is too hard to move or settle with the portion of the wall/building that is settling, so the mortar usually cracks upward towards the part of the wall/building that is settling. The second form of step cracking can be found in a “V” shape. This is usually found underneath failing windows or above failing arches. This is a sign that the window or arch is no longer supporting the weight as designed or that water is not being shed properly and is washing out the mortar. If allowed to continue, step cracks can allow moisture into the mortar and bricks, develop buckling, or even collapse altogether.
Pointing/Repointing
Pointing is the visible mortar. It should be water tight and run the full length of the bricks on all sides including the depth of the brick into the wall. Historically this was primarily a lime mortar. Repointing is the process of scraping the old pointing or mortar out of the wall and off the bricks leaving only 30mm of mortar in the deepest plain of the brick. This will hold the bricks in place long enough to repoint. When repointing, it is important to know what type of mortar was used previously.[5] Replacing a lime cement mortar with a Portland cement mortar will cause mass failure of historic bricks. The Portland is harder than the brick itself. This does not allow moisture to evaporate out of the bricks. Trapping moisture will cause the bricks to deteriorate while leaving behind the Portland cells.[6]
References
- ↑ The Wise Handbook of Masonry and Waterproofing (New York: Wm. H. Wise & Co., Inc., 1953), 193.
- ↑ Robert A. Young, Historic Preservation Technology (Hoboken, New Jersey: John Wiley & Sons, 2008), 102.
- ↑ Martin E. Weaver, Conserving Buildings: A Manual of Techniques and Materials. Rev. ed. (Hoboken, New Jersey: John Wiley & Sons, 1997), 103-109.
- ↑ Robert A. Young, Historic Preservation Technology (Hoboken, New Jersey: John Wiley & Sons, 2008), 100.
- ↑ Robert C. Mack and John P. Speweik, "Repointing Mortar Joints in Historic Masonry Buildings" NPS Department of the Interior - Technical Preservation Services - Preservation Briefs #2, October 1988, http://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm.
- ↑ Bernard M. Feilden. Conservation of Historic Buildings, 3rd ed. (Burlington, Massachusetts: Architectural Press, 2009), 71.
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