Is Your Foundation Crack Getting Wider?

Almost every foundation has cracks, and most of them are nothing. Concrete shrinks as it cures, and the thin vertical lines that show up in the first year or two are normal behaviour. The job is telling those apart from the cracks that actually mean something. A crack that keeps getting wider is the one that earns a closer look, so here’s how to read yours.

The four things to check

You can do most of the triage yourself before anyone comes out:

• Width. Hairlines under about an eighth of an inch that stay put are ordinary. Past a quarter inch deserves attention.
• Direction. Vertical and slightly diagonal cracks are the common, mostly harmless kind. A horizontal crack in a block wall is soil pressure pushing in, and that goes straight onto the serious list.
• Movement. A crack that grows every year, or opens and closes with the seasons, has a live cause that filler alone won’t fix.
• Offset. If one side of the crack sits proud of the other, the wall has shifted, not just shrunk.

A vertical hairline that hasn’t changed in three years is very different from a crack that was hairline last spring and is pencil-wide now.

How to watch a crack properly

If you’re not sure whether it’s moving, measure it over time instead of guessing. Mark both ends with a pencil and write the date on the wall. Draw a short line across the crack at its widest point too. Check it after a few weeks and again after a freeze and a thaw. If the marks separate, the pencil lines no longer meet, or the crack reaches past where you dated it, something is still moving and the cause needs attention along with the crack. If nothing changes over a season, you’re almost certainly looking at harmless shrinkage.

Why foundation cracks grow in Southern Ontario

When a crack keeps moving, the reason is almost always outside the wall. The region’s clay soils hold water and swell when saturated, and that swollen clay presses on the foundation. Tired weeping tile or a downspout dumping at a corner makes it worse by keeping the ground around the wall wet. Block walls take that pressure sideways, which is where bowing and the stair-step cracking through the joints come from. So a growing crack is often a drainage and soil-pressure story, and fixing only the crack while ignoring the water just rents you a few dry months.

What to do about it

The fix depends on what the crack is doing:

• A leaking but stable crack in a poured wall is usually injected full-depth from the inside, sealing it against water and, with epoxy, bonding the wall back together. That’s the common, undramatic case. Foundation repair covers how the call gets made.
• A crack that leaks in several places, or along the whole wall, is a pressure problem, and the real fix is water management, not more filler.
• A bowing wall or horizontal crack is structural and gets reinforced, but the saturated clay outside has to be dealt with too or the wall keeps losing.

One thing to be wary of in either direction: a harmless hairline quoted as a major structural job, and a serious moving crack smeared shut with caulk and called fixed. Both cost you, just in opposite directions. Anyone quoting structural work should be able to point at the evidence: measurements, photos, the pattern.

Get a straight answer

If your crack is growing, or you just can’t tell, a free assessment is the cheapest move you can make. We measure it, tell you plainly whether it’s the harmless kind that just needs watching or something with a live cause, and put that in writing. If it turns out to be nothing, the assessment will say so, and that’s a perfectly good outcome.