Many older homes are built on brick foundations. These are designed to last for many decades, but even the best-built foundations can eventually develop problems. Frost heave, slow water leaks and excessive pressure from earth on the exterior can cause serious damage to a brick foundation. Some brick problems can be corrected, but others may require you to replace entire sections. Catching trouble early can help you fix problems with a minimum of effort and expense.
Bulging bricks in the above-ground portion of the foundation are usually the result of a bond failure between bricks or courses. This problem could cause a disastrous foundation failure in short order. Bulges are often caused when water or frost get trapped between the bricks. Poorly directed roof runoff often causes foundations to bulge at the frost line. The solution to this problem is tuck-pointing, the reapplication of mortar between the bricks, or complete rebuilding of part of the foundation.
When roof runoff water falls close to or over the foundation, it may gradually erode the mortar between bricks, loosening them. Loose bricks may also occur when adjacent wooden nailing blocks and wood joists are damaged by rot or insects. To repair loose bricks, clean out all existing mortar and tuck-point the bricks by applying new mortar. Replace any missing bricks with new ones.
Stair-stepped or diagonal cracks in your foundation may indicate settling, frost damage or thermal expansion in foundations without expansion joints. This problem tends to occur near the corners of buildings, where roof spillage often falls. Cracks often cause damage to windows and walls immediately above them when the house shifts. Cracks under 1/4 inch in width should be checked regularly to ensure they are not growing larger, while cracks between 3/8 and 1/2 inch may indicate a true foundation failure. Monitor cracks and stabilize the foundation by replacing cracked bricks as necessary.
Sandblasting and high-pressure water cleanings can damage the surface of brittle old bricks enough to affect their stability. Many bricks are endowed with a hard exterior surface formed during their initial firing, which protects the softer material inside. Eroding this surface with abrasive cleaning methods exposes the inside to water and frost. Damaged bricks absorb water and may crack or break. Avoid sandblasting or other strongly abrasive cleaning methods in favor of slower but gentler techniques and check bricks periodically to see if the surfaces of any are obviously compromised.
Many older foundations have been repaired or patched by a previous owner. This isn't always done correctly, though. It is not uncommon for past repairs to have used overly hard mortar, which often results in cracked bricks or damage to other parts of the foundation. Never use a mortar composed of a high percentage of Portland cement to repair an old wall originally built with softer lime-sand mortar--the difference in their hardness and water absorption rates can damage the wall. If your wall has been incorrectly repaired, the only remedy is to chisel out all the bad mortar and replace it with an appropriate material.