Slab

CRACKED SLABS
By Al Virtue

    There are areas of a house that experienced inspectors always investigate for possible slab problems. Most cracked slabs are found at the visible section of the exterior foundation. I always closely inspect the perimeter of the slab to check for cracks. Other good indicators are cracks below the furnace, inside the filter compartment, uneven floors, cracked tiles, buckled linoleum or domed floors at the center of a room. These are all possible signs of cracking.

It is important to pay particular attention to the middle third of the slab and where the slab is at its narrow point. This is where there should be an expansion joint, but almost never is. The slab will often times make its own expansion joint. Many times this will happen at the front door running through to the patio door.

Some indirect signs of foundation movement can be found at doorframes that are out of square, or at cracks that pass from one medium to another (also called pattern cracks). For example, a stucco crack 1/8 inch with a crack at the inside drywall and then one at the ceiling is a crack that changes medium can be an indication of a movement.

Attic framing can also show unusual signs of separation at connection points. When foundation cracks, and movement occurs, the foundation tends to be the hinge point and the cracks become larger, or V-shaped. As you go higher into the structure, the cracks or separations increase in size.

Any stucco or drywall cracks that are parallel with a hillside slope can be an indication of possible slab cracking and slope movement. These types of cracks can be the most serious, because they are symptoms of slope movement.

Dome shape elevation with cracks running to the top of the dome is usually due to expansion soils and is related to drainage. When expansion soil gets wet, it increases in size and can cause severe cracking and damage to the slab, especially at weak or thin sections of the slab. The best way to find cracks in slabs is to have the floor covering removed. Unfortunately this in impractical in many instances, in that houses are typically furnished and floor coverings are secured in place.

If there is no displacement of slab cracks and no other cracking in drywall or stucco, and the door frames are square, and the crack does not appear to have a relationship to a slope, then the typical repair would simply be epoxy injection.

Severity of the concrete crack, many times, depends on whether the crack is caused by soil movement, weak concrete or simply shrinkage. A crack less than 1/8 inch that tapers down to a hairline crack at ends would most likely be due to shrinkage. More serious cracks might be parallel with a slope, or over 1/4 inch with offsets from one side to another. These cracks may or may not indicate major problems, however, a qualified state registered engineer should evaluate and determine the cause, effect and remedy.