Symptoms
- Hairline or wider crack across the concrete surface
- Crack may run straight or branch off
- One side of the crack may be slightly higher than the other
- Crack in a garage, basement, or utility room floor
Likely causes
- CommonNormal concrete shrinkage as it curesConcrete shrinks slightly while curing, and minor shrinkage cracks are extremely common and usually harmless.
- PossibleSettling of the soil beneath the slabUneven settling can create cracks, sometimes with a slight height difference across the crack.
- PossibleTemperature and moisture-related expansion and contractionConcrete moves slightly with weather, and cracks can form at natural stress points.
- Less commonStructural issue with the foundation or slabWide, actively growing, or offset cracks can indicate a more serious foundation problem.
What to do
- Measure the crack's width; hairline cracks under about 1/8 inch with no height difference are typically just cosmetic.
- Check if one side of the crack sits higher than the other, which can indicate settling rather than simple shrinkage.
- Clean the crack of debris and loose material with a wire brush and shop vacuum.
- For a stable, narrow crack, fill it with a concrete crack filler or self-leveling caulk designed for slabs, following the product's application instructions.
- For a wider crack, a concrete patching compound or epoxy crack injection may hold up better than caulk alone.
- Monitor the crack over the following months by marking its ends with a pencil and date to see if it's actively growing.
- If the crack widens, one side rises, or you notice similar cracking in nearby walls, get a foundation professional to assess it.
Tools and parts
- Wire brush
- Shop vacuum
- Caulk gun
Concrete crack fillerSearch: “concrete crack filler sealant”
When to call a pro
Call a foundation specialist if the crack is wide, offset, or actively growing, since that points to a structural rather than cosmetic issue.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.