Which Cracks Are Cosmetic and Which Aren't

Foundation crack repair in Toronto is straightforward once you know what kind of crack you have — and the assessment matters far more than the repair method.

The ten-second assessment

Vertical, hairline, under 3 mm

Concrete shrinkage. As a poured wall cures it loses volume and cracks. This typically happens in the first year of the building's life and then stops.

Structurally irrelevant. Worth repairing only if it is letting water in.

Diagonal from a window or door corner

Stress concentration at an opening, which is where a wall is weakest. Usually benign, though a diagonal crack that is widening over time can be an early settlement signal.

Worth monitoring: mark each end with a pencil and the date, and check in six months.

Horizontal, partway up the wall

Take this one seriously. A horizontal crack usually means lateral pressure from saturated soil pushing the wall inward — the wall is bending, and the crack is where it hinged.

Look along the wall from one end. If there is any visible bow, get a structural engineer involved before anything is sealed.

Stair-step through block mortar joints

Differential settlement: one part of the foundation has moved relative to another. The crack follows the mortar because that is the weakest path.

Whether it needs action depends entirely on whether the movement has stopped. An old, stable settlement crack in a hundred-year-old house is often fine. One that appeared last spring is not.

Displaced faces

Run a finger across the crack. If the two sides are no longer flush — one has moved out of plane relative to the other — that is displacement, not cracking, and it always warrants an engineer.

How injection actually works

Injection ports are fixed along the crack at intervals, and the crack face between them is sealed with a surface paste so nothing escapes under pressure.

Resin is then injected under pressure through the lowest port until it appears at the next one up, and so on to the top. This fills the crack through the entire thickness of the wall, not just the visible surface.

Once cured, the surface paste and ports are removed.

Polyurethane is the usual choice for a leaking crack: it expands on contact with moisture and stays slightly flexible, tolerating seasonal movement. Epoxy cures rigid and stronger than the concrete around it, and is used where the repair needs to restore structural continuity.

Why surface patching fails

Hydraulic cement and patching compounds from the hardware store seal the face of the crack and nothing more.

Water arriving under hydrostatic pressure from outside does not stop at a 3 mm surface skin. It travels through the wall and finds the edge of the patch, or simply pushes it off. Most surface patches fail within a season, and they make the subsequent proper repair slightly harder by contaminating the crack face.

When the crack is a symptom, not the problem

Worth pausing on this before you spend anything.

Cracks caused by soil pressure and settlement are usually driven by moisture cycling in Toronto's clay soils. Clay swells when wet and shrinks when dry, and it does that every year.

If your grading falls toward the house, or your downspouts discharge at the foundation, you are driving that cycle. Sealing the crack without fixing the water means you will be sealing another crack in a few years.

We have written up the ways this goes wrong, including repairs that were technically correct and still failed, onwhat can go wrong.

What it costs

Where several cracks are leaking along one wall, or water is arriving at the floor-wall joint rather than at a point, the problem is drainage rather than the cracks — seeinterior waterproofing.