Use Right Bricks, and Keep Moisture Away
Weather is the primary enemy of bricks, especially wet, cold weather and extremes of temperature.
Brick is durable, long-lasting and virtually maintenance-free compared with most other types of building materials. Some bricks fired and stacked thousands of years ago survive today. But brickwork does eventually erode.
You won’t find many problems with post-World War II brick houses. But in many older homes, especially century-old ones, you’ll find corrosive effects at work. You won’t see much change from year to year. But slowly, almost imperceptibly, cycles of heat and cold, along with rain, wear down brick walls.
Brick is made from clay that’s molded and fired in a high-temperature kiln. Its hardness depends on the kiln temperature and firing time. Different clay compositions and length of firing account for most variations in brick color.
Hard or soft, bricks are able to stand up against any single weathering onslaught. But two forces--water and freezing temperatures--can break down a brick wall. Water that soaks into the brick and then freezes will begin to shatter the brick’s internal structure.
To prevent this problem, brick manufacturers grade their bricks according to the weather extremes they must face.
Severe weathering brick, classified as SW, is the hardest and most dense. It absorbs the least amount of water, which makes it less vulnerable to freezing weather. Moderate weathering (MW) brick is not quite as hard as SW and absorbs more water. Negligible weathering (NW) brick is the softest and most absorbent.
Except in regions that rarely see freezing temperatures, masons should use only SW and MW bricks on exterior projects. And in all regions, without exception, SW bricks should be used wherever the construction is in contact with the ground.
Most of the deterioration in brickwork happens when the mortar joints fail. Bricks can’t flex when the brick wall expands and contracts with changes in temperature. To keep the wall from cracking, the mortar acts like an elastic cushion to absorb most of the movement.
Diagonal cracks along the mortar joints indicate that the supporting foundation has settled or shifted unevenly. The brick wall couldn’t absorb the movement, so it cracked at the mortar joints. Rain blew in through the cracks and broke down the mortar.
To solve the problem, rainwater should be routed away from the foundation of the building. Then, by “pointing” or “tuck pointing,” large cracks in the joints must be repacked with mortar.
If bricks are used for horizontal surfaces such as windowsills and the tops of brick walls, they will eventually need repairs because water will collect there, causing the mortar joints to deteriorate. Ideally, such surfaces should be capped with stone, concrete or other material.
Dampness rising from the ground often deposits a powdery film, called efflorescence, on the face of the bricks when the moisture evaporates. It’s harmless and can be easily scrubbed away with a dry, stiff brush. But it will return unless the surrounding soil is kept dry and walls are capped with metal flashing, concrete or a stone cap--called a “coping”--to keep moisture out.