Repair? Patch is more the word, because it's impossible to truly stitch together a cracked concrete slab. Also, your patch will look like a patch; it will not blend it with the rest of the floor, though it will look better than before.
The great thing is that it's an easy job, requiring few materials. Not only that, the materials (and tools) are inexpensive.
- 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.
Next, 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 this crack and get down to more solid material.
- Use a wire brush and Shop Vac to clean out all the junk from the crack. The crack needs to be completely clean and free of chunks, pebbles, dirt, dust, weeds--anything that might hinder the adhesion of your patching material.
- Brush on a bonding adhesive to the entire crack. Let the adhesive thoroughly dry.
- Mix up your concrete patch material. Do not buy a bag of ready-mix concrete and expect to use this for patching. Instead, buy a material designed specifically for patching concrete.
- Push the concrete patch compound into the crack as far as possible with a paint stirring stick. Make sure that no voids are in the patch material.
- Let this deep, below-grade patch material thoroughly harden.
- Trowel your next layer of concrete patch compound to bring the patch up to grade.
- 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 want until the material has dried, it's not possible to do this.
- Cover area with plastic and weigh it down so that it does not blow away. Let cure for 3 days.
- Chipping out the "good" concrete in the initial stages may give you some pause. But you'll soon find that this "good" concrete isn't so good. It's probably quite unstable.
Just don't go too far. After you expand a crack too far, it no longer becomes a job of patching. By that point, you'll need to fix the hole with a mix of concrete.
- For the concrete patch, I recommend Dap 31084 Concrete Patch Interior and Exterior 1-Quart. It's cheap and widely available.
- Why use concrete bonding adhesive? This eliminates the need to roughen up the surface for new concrete to adhere.
- Alternatively, you can squirt some Liquid Nails Concrete Repair into the crack. But be forewarned: this is nothing more than super-strong caulk. It will do nothing to cover up the crack.
- Warning: this type of patch is not appropriate for basements. You'll need to use hydraulic patch compound for basements.
What You Need
- 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
- Large sponge
- Wire brush
- Shop vacuum
- Safety glasses