Concrete flooring will almost certainly crack eventually. Often, it's just a matter of luck and time. Stresses, such as tree roots, shifting ground, earthquakes, flooding, rising water tables, and even heavy appliances, can contribute to cracking. Concrete can also crack from internal stresses that are unavoidable. Basement floors especially are prone to cracking since they are below-grade areas and thus are closer to tree roots and water tables. It doesn't help that some basement concrete floors are poured quickly and without much attention paid to quality.
Concrete floor patching is your solution to minor cracks that are more about aesthetics, moisture intrusion, and insect infestation than about major structural integrity. Cracks make your basement look bad and they do not help your property's resale value. Rising water can find its way through cracks. Carpenter ants, termites, and even vermin can find their way through cracks. When you patch a cracked concrete slab, your work will look like a patch. It will not blend it with the rest of the floor unless you paint and seal the concrete.
The great thing about concrete patching is that it's an easy job and requires few materials. Not only that, the materials and tools are inexpensive.
Tools and Materials
- Concrete or mortar chisel, not a wood chisel
- Wooden paint stirring stick
- Concrete bonding adhesive, like Quikrete Concrete Bonding Adhesive
- Concrete patch compound like DAP 31084 Concrete Patch Interior and Exterior 1-Quart, an inexpensive, easily available concrete patch material
- Large sponge
- Wire brush
- Shop vacuum
- Safety glasses
- Trowel or large putty knife
Remove Chunks of Concrete
Begin by running your chisel through the crack to remove any obviously loose chunks of concrete. Pull them from the crack with your fingers, if possible, or by knocking them free with a dull screwdriver.
Taper Down the Crack
Use the chisel and hammer to taper down the sides of the crack. This may seem counter-intuitive, but you need to get rid of the unstable edges of the crack and get down to the more solid material. Chipping out the good concrete in these initial stages may give you some pause. But you'll sometimes find that this good concrete isn't so stable after all. Be careful of extending the taper too far, though.
Clean out the Crack
Use a wire brush and a shop vacuum to clean out all the debris from the crack. The crack needs to be completely clean and free of chunks, pebbles, dirt, dust, weeds, and anything that might hinder the adhesion of your patching material.
Apply the Bonding Adhesive
Brush on a bonding adhesive to the entire crack. Let the adhesive thoroughly dry. Concrete bonding adhesive eliminates the need to roughen up the surface for the new concrete to adhere.
Mix the Concrete Patch Material
Mix up your concrete patch material. Do not use ready-mix concrete such as Quikrete as this is not suitable for patching. Instead, buy a material designed specifically for patching concrete.
Apply the First Layer
Push the concrete patch compound into the crack as far as possible with a paint stirring stick. Make sure that no voids remain in the patch material. Let this deep, below-grade patch material thoroughly harden. The idea with this first layer is to occupy large areas toward the bottom of the crack. Do not bring the patch material up to the level of the concrete floor yet.
Apply the Second Layer
Trowel your next layer of concrete patch compound to bring the patch up so it is level with the slab surface. Smooth out the patch with the flat face of your trowel. To further smooth out your work, use a wet sponge while the patching material is still wet. If you wait until the material dries, it will not be possible to work with the material any longer.
Let the Patch Cure
Cover the area with plastic and weight it down so that it does not blow away. Let it cure for three days or for the period recommended on the product packaging.
An Alternative for Narrow Cracks
Thin cracks in concrete that are less than 1/4-inch wide are even easier to patch. Purchase a liquid concrete patch repair, such as Liquid Nails Concrete Repair or Quikrete Acrylic Concrete Patch. These watery repair materials are superb for narrow cracks as they conform to the crack.