I don’t know about you, but most people I talk with get a little panicked when they see any type of crack in their foundation. But the real question is which cracks are worth worrying about and which ones are not?
Foundation cracks are usually signs of foundation damage, but can mean very different things depending on the material from which a foundation is made, the location, size, and shape of the foundation crack, and other site observations. The more you know about the cause, history, and movement of the crack the easier it will be to determine whether or not you need to take action.
Here are a few suggestions for evaluating foundation cracks you encounter:
Look at shape, pattern, frequency of occurrence, correlation with cracks in floors, and location in the wall (corners, center), as well as length, width, continuity, and theage of wall.
Shrinkage cracks are usually uniform in width or vee-shaped, wider at top and diminishing or stopping before reaching the bottom of the foundation wall. A wall crack which continues into the floor is likely to involve the building footings. Shrinkage cracking is due to conditions at original construction: poor mix, rapid curing, possibly other conditions. Shrinkage cracks are less likely to require structural monitoring and repair in poured concrete as they would be expected to continue after initial curing.
Concrete block foundation walls shrink as they cure. They rarely expand much on exposure to moisture and temperature variations. In concrete block walls shrinkage cracks are likely to be uniform in width and usually occur towards the center of a concrete masonry unit (CMU) wall. The wall is stronger at the building corners.
Brick walls do not normally shrink, but rather, grow indefinitely. If you see a crack in a brick wall it’s more likely due to movement in the structure, a support problem, or due to thermal expansion. Cracks in structural brick walls may be very serious if the bond courses are broken as there is then a risk of sudden catastrophic wall collapse. Cracks and especially bulged cracked brick walls need immediate expert investigation.
Stone foundation walls do not normally crack through individual stones, but the wall may be bulged and cracked due to damage from frost, loading from driving vehicles near the wall, or by the removal of stones to pass piping or make doorways. As with other cases of foundation movement, a diagnosis of the cause, amount of movement, and effects on structure are needed to decide what repair may be needed.