When is a basement floor crack a problem? When it leaks water, when one side sits higher than the other, when it keeps getting wider, or when the floor around it is heaving or sinking. A thin, dry, flat crack on its own usually is not.
Is It Common for Concrete Floors to Crack?
Yes. Concrete shrinks as it cures and dries, and a basement slab cracks as it dries. Many slabs are cut with control joints so the cracks form there. These hairline shrinkage cracks are common and are normal.
The basement floor slab also usually does not hold up the walls. In most houses the walls sit on footings, so a slab crack alone is often a floor problem.
How Can You Tell if a Crack Is Structural?
Look at what the crack is doing, not just that it is there.
- Height difference. If one edge is higher than the other, the slab has moved. Run your hand across it.
- Widening. Mark the ends and the width with a pencil and the date. If it grows over the months, it is still moving.
- Water. Damp edges, staining, or water coming up through the crack.
- Heave or sinking. A floor that bulges up, dips down, or makes doors and stairs fit differently.
- Matching wall cracks. Floor cracks that line up with cracks in the foundation walls.
In Winnipeg, clay soil that swells and shrinks can heave basement slabs and leave floors uneven.
How Big of a Crack Is Acceptable in Concrete?
There is no single safe width. A hairline crack that is dry and level is usually cosmetic. What matters is movement: a crack that stays the same is less of a concern than a smaller one that keeps opening, shifts in height, or lets water in.
What Should You Do About a Problem Floor Crack?
Note which signs you see and when they started. If the crack only lets water in, see our guide to cracks that leak water. Our foundation crack repair cost guide covers what a repair quote depends on.
Need a Floor Crack Looked At?
Read our foundation crack repair page or call (431) 445-7139.