Cracks in concrete are almost inevitable; it’s just what concrete does! It becomes a problem when it is in the weather and exposed to wet conditions and in many areas of the country freezing conditions. Water seeps in under the concrete slab and erodes the underlying soil; if the water freezes it will actually enlarge the cracks or in some instances uplift the section of concrete.
If the concrete slab is outdoors, such as a driveway or patio, the cracks need to be sealed properly to keep water from seeping under the slab.
To seal crack in a concrete slab:
• Remove any debris or loose concrete in the crack using a screwdriver, followed by a wire brush.
• Use a broom or leaf blower to clean out the crack.
• Fill the crack with concrete repair caulk, such as Polyurethane Concrete Crack Sealant from Quikrete.
Other brands are available but this is a product that I have used.
On cracks that are wider than 1/4” push foam backer rod into the crack with a screwdriver, so it’s 1/2” below the surface, then fill the crack with concrete repair caulk.
If cracks are related to tree roots, underground voids from decaying organic material, expansive soils or just poor design and construction, sealing the cracks will only delay the inevitable and that is the correction of the problem and replacement of the concrete.