Learning how to repair a garage floor doesn’t have to be as scary as it sounds. You may be surprised to learn that many repairs can be done easily by yourself and for less expense than you think. Typically with a garage floor there are three types of repairs that are the most common; surface cracks, pitting, and spalling. Pitting and spalling can be just as easy to repair as most cracks. It just takes a little more work.
If you are applying a sealer, paint, or an epoxy system, then you will want to make sure your floor is repaired properly to make it is as blemish free as possible. If you are covering your floor with a tile or mat flooring then repair may not be necessary unless you are trying to stop a continuing problem like pitting or spalling or are worried about water penetration with a larger crack.
Garage floors crack – period. Concrete is not a ductile material, meaning that it neither stretches nor bends without breaking. It does shrink and expand with temperature however and as a result it cracks. Most floors have contraction joints built into the slab that allow for this cracking. These are usually those deep grooves that you see in the concrete that appear to divide a typical two-car garage into four separate slabs. These grooves create a weakened line in the concrete that encourages cracks to follow it.
As well as this works, you still can unfortunately get cracks in other parts of the slab due to the settling of the earth underneath the slab, poor contraction joints, or other variables beyond your control. If it’s a fairly new slab doing this, it may continue for some time requiring the occasional crack maintenance until the slab finally settles and cures. The good news is that the majority of cracks is cosmetic and not structural in nature and can be repaired to accept most any garage flooring.
Repairing Cracks in Your Garage Floor
If you are applying a coating to your garage floor, most cracks can be repaired with an epoxy or polyurethane based crack filling compound available from most home improve centers or found online. Some come in a small pail and may require some mixing, while others are available in a cartridge and require a caulking gun to use. Make sure the areas around the cracks have been cleaned and that any large cracks have been washed out with a high pressure hose or a pressure washer.
For cracks that are smaller than 1/8″, use a wire brush on the crack and then sweep it clean. You can then fill the crack with the repair compound and use a putty knife to smooth it over. For larger cracks you ideally want to chase the crack using a 4” grinder with a masonry wheel, clean it out, and then fill it with the repair compound using your putt knife to trowel it smooth. This is done to remove any weak edges surrounding the crack. If you don’t have a grinder you can always chase the crack with a hammer and chisel.
If you have a crack that is 1/2 wide or larger or that is exceptionally deep, you will want to chisel out the crack and try to create a backward-angled cut. You can also use a grinder with a masonry wheel for this as well. Doing this will help prevent the repair from lifting. Fill the crack with fine silica sand till it is about 3/4″ from the surface and then apply your repair compound to it. The reason for this is to avoid sinking of the repair compound as it slowly fills the crack while curing. 100% solids epoxy mixed with silica sand is great filler for larger cracks. Rust-Oleum has a concrete and patch repair product that works extremely well for this.
After doing this, fill the rest of the crack and smooth over with your putty knife. After is has cured, you may have some low spots to fill over one more time. If it wasn’t troweled over smooth you can gently grind the repair to create an even surface. Don’t forget to fill in any small divots or holes you may have in the concrete as well.
Repairing Spalled and Pitted Garage Floors
Pitting of a garage floor can be caused by improper finishing of the concrete or a bad mix. Sometimes it is most notable at the edges where contraction joints are or where it might meet up with another slab. Spalling on the other hand is generally caused by freeze-thaw cycles in colder climates and aggravated by deicing salts. Water migrates into the surface of the concrete and freezes. The expansion of the water causes microscopic damage to the concrete and after a few years of this it starts to breakup in small dusty pieces and chips.
For repair of the floor you will want to purchase a polymer-modified cement topping or patching mix. Most of these mix easily with water. Make sure to read the directions carefully. Some may require a bonding agent that needs to be brushed on the concrete before you apply the patching compound. Be sure to chip out any loose pieces of concrete and wire brush well before you clean the floor. When the floor is ready, apply the mix over the pitted areas using a trowel. Some mixes are self-leveling and can be applied with a metal squeegee. Be sure to feather-in smooth and let dry according to the instructions. You may need an additional application to fill in any small divots or low spots created from the mix settling. You should end up with a nicely repaired surface that won’t be noticeable once it is painted or epoxied over. See this article for more information on repairing spalled or pitted concrete.
One thing to remember if you are planning on applying a clear coat sealer to your bare concrete is that any patchwork that you have done will be enhanced by the sealer. However, if you are applying a colored paint or colored epoxy sealer then you should have the appearance of a nicely smooth concrete slab free of blemishes. With the multiple coat epoxy floor coatings you shouldn’t have to worry about filling the smaller hairline cracks as the thicker surface coat of epoxy will do this for you. Do not use any latex based or silicone concrete fillers and sealers for your crack repair. These are flexible compounds that will shrink over time, delaminate, and cause you grief.
Low Spots and Other Repair Issues
One thing we did not cover is sunken slabs. Unfortunately these are not a quick fix and can be costly to repair. These can be caused from severe settling to poorly reinforced slabs or something worse such as underground water issues. Sometimes the only alternative is to tear out the old slab, and pour a new one. However, if you just have low spots in your slab that collect water due to a bad finishing job, there is an answer. You can use a self-leveling polymer-modified topping to fill in those low spots. Use a metal squeegee when you apply and be sure you don’t fill in any of your contraction joints. If you do, you can scrape it out later as it starts to harden. Just make sure the product you use is designed for outdoor use.
Properly completed, repairs can last for years if not the lifetime of the garage floor . If you can patch a wall before painting, then you have the skills to do the same for your floor and avoid the much more expensive option of having someone do it for you.