Most homes built prior to 1920 have stone foundations, often with stone below-grade and brick above-grade. Loose stones and cracks in mortar joints are common, particularly at exterior corners. Buyers can get upset when they can pull loose bricks from a foundation wall, but all residential brick walls on top of stone foundations that we have seen contain at least a double brick wall. If the outer bricks are loose and the house is still standing, the weight of the house is on the inner brick wall. The outer wall can be easily repaired. The most common cause of corner cracks and eroded mortar is roof water. When water rounds over the mortar in masonry, the mortar slowly washes out. Eventually, the mortar loosens and pieces may even fall out.
Roof water from poor drainage or dispersal at the corner of a building can cause symmetrical, diagonal settling cracks at the foundation. Over a long period of time, the soil under a corner of a foundation can shift away because of excess moisture, causing the corner to settle relative to the adjacent walls.
Generally, this condition is not serious, and installation of downspout elbows and splash blocks, along with grading improvements, will stop the corner settlement. Then the cracks can be mortared.
Starting in the 1930’s, most homes were built on poured concrete foundations. Shrinkage cracks are normal and quite common in concrete foundation walls and floor slabs. This type of crack is either vertical or diagonal, and radiates from wall openings such as windows or between floor penetrations such as beam-support columns. Cracks in concrete may widen in dry weather and become narrower when it’s humid. More serious cracks will increase in size over time.
Cracks are common in masonry because masonry products such as concrete and plaster are brittle and rigid, but are supported on materials that may not be equally rigid. Plaster walls are attached to flexible wood structures and foundations rest upon compressible soil. In addition, home components expand and contract with fluctuations in temperature as well as increases and decreases in relative humidity. Wood and other construction materials shrink when they lose moisture in dry weather, and expand in humid weather.
Buildings constructed between 1930 and 1950 may have plaster on metal lath; metal lath walls tend to be much stiffer and are thus not as prone to developing cracks. Sometimes, you can distinguish between plaster on wood lath and plaster on metal lath by hitting the wall.
The age of the crack cannot be determined with accuracy. Often fresh cracks are clean whereas older cracks might have dirt or insects in them. Surfaces that have been painted may also give you a clue as a to the age of the crack.
If you have concerns about cracks on your brick, poured concrete, cinder block walls, don’t hesitate to contact Basements Love Us as we are certified in structural repair. Basements Love Us also has structural engineers on staff to provide guidance for more severe issues. We can assist through the permitting process to expedite the repair and assure the home is up to codeTags: structural Repair