Not every foundation crack is a crisis, but none of them should be ignored. Knowing which kind you are looking at is the difference between a $40 tube of sealant and a structural repair bill.

Why Foundations Crack

Concrete shrinks as it cures, and soil moves as it wets and dries. Most hairline vertical cracks are ordinary shrinkage. Horizontal cracks, stepped cracks in block work, and anything wider than a coin are signs of pressure or settlement — a very different problem.

When DIY Makes Sense

A narrow, stable, vertical crack in a poured wall that is dry and not growing is a reasonable DIY repair with an injection kit. Clean it out, follow the product's cure times, and mark the ends so you can confirm it stays put.

• Crack is vertical, under 3mm, and has not moved in months.

• No water is coming through and no efflorescence is present.

• Floors above are level and doors still close properly.

When to Hire a Professional

Call someone if the crack is horizontal or stepped, is wider than a coin, is leaking, or is still moving. Those point to soil pressure, drainage failure, or settlement — and sealing the surface just hides the evidence while the cause keeps working.

The Cost of Waiting

A monitored, properly repaired crack is usually a few hundred dollars. The same crack left through two winters of freeze-thaw and saturated soil can turn into underpinning, structural bracing, and finished rooms taken back to bare walls.