Foundation Cracks near you

Shrinkage cracks form as fresh concrete dries and contracts. They're usually thin and fairly even along their length, often vertical or slightly diagonal, and they tend to start at a weak point such as the corner of a basement window. Structural cracks come from forces acting on the wall after it was built, such as settlement, soil pressure, frost or heaving, and their shape usually gives them away.

Watching a crack costs nothing and tells an engineer or contractor a great deal. Everything below is done from inside the basement or from the ground outside, without digging, chiselling or prying at the crack.

Most leaking cracks in poured concrete walls are repaired from inside by injection. The technician cleans the crack, fixes small injection ports along it and seals the surface between them, then pumps resin in from the lowest port upward until the crack is filled through the thickness of the wall. Once the resin has cured, the ports are removed and the surface is tidied up.

Frost plays a part almost everywhere in Canada. Water that works into a crack or saturates the soil against the wall expands as it freezes, which can widen an existing crack a little each winter, and frozen soil gripping the upper part of the wall can push against it. Soil freezing under a shallow footing, such as a porch or an unheated addition, can lift it. That's why a crack is best judged over a full year rather than on a single visit.

Clay soils add another kind of movement: fine-grained clays swell when wet and shrink as they dry, so a long dry summer or a large tree drawing water near the house can let part of a foundation settle. Clay soils are common in parts of Quebec and eastern Ontario. Parts of Ottawa sit on what the city calls sensitive marine clay, or Champlain Sea clay, and its tree-planting guidelines for these soils grew out of cases where trees were identified as a significant contributing factor in foundation damage. On clay, keeping the moisture around the foundation steady, through good drainage and sensible tree placement, matters as much as the crack repair itself.

A crack that lets water in is also an opening to the soil beneath the house. Health Canada lists cracks in foundation floors and walls, construction joints, gaps around service pipes, floor drains and sumps among the ways radon gets into a home, and notes that radon can be found in almost all Canadian homes.

Sealing cracks and the joint between the wall and the floor can help lower radon levels, but Health Canada says it is not a standalone technique, because it's hard to find, reach and permanently seal every opening. The only way to know your home's radon level is to test, which is worth doing before and after any major foundation or basement work.

An engineer's opinion on a crack is a modest service next to the cost of the wrong repair, and it tells you whether injection is enough or whether the cause must be dealt with first. Call one when you see any of the following.