Concrete flooring eventually will crack. 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.
Concrete patching is an easy job and requires few materials. Not only that, the materials and tools are inexpensive. Patching takes less than an hour, but the curing process usually takes several days.
Equipment / Tools
- Wooden paint stirring stick
- Large sponge
- Wire brush
- Shop vacuum
- Trowel or large putty knife
- Safety glasses
- Concrete patch compound
- Concrete bonding adhesive
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 Crack
Wearing eye and hearing protection, use the chisel and hammer to taper down the sides of the crack. Be careful as you tap away at the edges of the crack. Frequently vacuum up debris so you can better see what you're doing.
The goal is to create a V-shaped section for the patch materials. Edges with 90 degrees are more prone to cracking.
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.
If the crack is very weedy, it's best to kill the weeds far in advance. Herbicides need several days or up to a week to loosen the weeds' roots.
Apply 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 Concrete Patch Material
Mix up your concrete patch material. Do not use ready-mix concrete as this is not suitable for patching. Instead, buy a material designed specifically for patching concrete. Use cool, clean water and a clean bucket that you don't need to reuse for other purposes (such as for washing the car).
Apply 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 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.
Let Patch Cure
Cover the area with plastic and weigh down the edges of the plastic so that it does not blow away. Let the patch cure for three days or for the period recommended on the product packaging.
Note that when you patch a cracked concrete slab, your work will look like a patch. It will not blend with the rest of the floor unless you paint and seal the concrete.