Garage floor cracking
easy 1–2 h
Tools: wire brush, shop vacuum, caulk gun, utility knife, straightedge, ruler · Materials: self-levelling polyurethane concrete crack sealant, backer rod for cracks wider than 6 mm, concrete sealer
Steps
- Measure the crack and check for a lip with a straightedge: a hairline to 6 mm (¼ inch) crack with both sides level is shrinkage and can be sealed; a lip or a crack that widens is settlement.
- Mark the ends and date them; recheck after a season before deciding it is stable.
- Chase the crack clean with a wire brush and vacuum out the dust; oil on the surface must be degreased or the sealant will not stick.
- Push backer rod into any crack wider than 6 mm so the sealant sits at the right depth, then fill with self-levelling polyurethane sealant and let it cure for a day.
- Seal the whole slab once the cracks are filled so water and road salt stop feeding the next crack.
- Keep the slab's edges from the downspouts and check that the driveway slopes away from the garage door.
Stop and call a pro if
- one side of the crack is higher than the other, the crack is wider than 1 cm (⅜ inch), or it keeps growing
- water comes up through the crack — the slab may be over a spring or a broken drain
- the slab has dropped at the door, or several cracks radiate from one corner
What a pro does that you can't
A concrete contractor lifts a settled slab with polyurethane foam injection, cuts control joints where the slab has none, or replaces a slab that has failed over poor fill.
DIY cost: $15–40 in sealant and backer rod; $30–60 for slab sealer