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 garage 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 repairs may not be necessary unless you are trying to stop a continuing problem like pitting and spalling or you are worried about water penetration.
Why garage floors 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 or saw cut joints 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 the groove instead of wondering across the surface.
As well as contraction joints work though, you still can get cracks in other parts of the concrete due to the settling of the earth underneath the slab, curing issues, or other variables beyond your control. The good news is that the majority of cracks are cosmetic and not structural in nature. This means that they can be repaired to accept most any garage flooring.
Recommended crack repair products
Always use an epoxy, polyurethane, or polyurea based crack repair or crack filling compound that is sandable. These cure and harden at a strength greater than concrete and will prevent water intrusion as well. You can grind or sand them flush with the concrete and they will accept paint or an epoxy coating.
Do not use inexpensive water based or latex based concrete crack filler and repair products. This is what most home improvement centers carry since they are cheap and easy to use. The problem with them is that they are not sandable, they will not accept paint, and they will shrink over time and pull away from the repair. Do not use a self leveling sealant either as these are designed mostly for sealing control joints in the concrete.
One such example of an epoxy based crack repair product that we know works very well is Simpson Strong-Tie Crack-Pak. It comes in a 9 oz. cartridge that requires a caulking gun to apply it. The 2-part epoxy is separated inside the container. The self mixing cartridge tip eliminates the need to mix the 2-parts together and makes application easy.
Because it flows very easily, it’s a great choice for repairing garage floor cracks less than 1/8″ wide. For deep cracks or cracks larger than 1/8″ wide, you will want to partially fill the crack with clean play sand or silica sand first when using this product. This will slow the flow of epoxy from going deep into the crack and using more than necessary.
Another excellent crack repair product that we have experience with is PC-Concrete Epoxy Crack Repair. It is a thicker flowing epoxy that requires using a putty knife to work into the crack. It also works well for filling small holes and divots in the concrete. Like other cartridge epoxy repair products, it comes with a self mixing tip as well.
What we like about PC-Concrete is that it fully cures in only 4 hours. This means that you can repair your cracks and grind them flush the same day.
A third product that we can recommend is Rust-Oleum’s EpoxyShield Concrete Patch. This is a 2-part epoxy as well that requires you to mix the separate Part-A and Part-B materials together on a piece of cardboard or wood.
When mixing the two components together, be careful not to mix too much at any one time. The epoxy does set fairly quick and you will only have a short time to use it. If your repairs are not all ready to be filled, you will run out of working time and the epoxy will become too thick to use.
You can sometimes find it at most home improvement centers or you can purchase it here from Amazon
If you are repairing numerous cracks larger than 1/4″ wide, then your best bet would be an epoxy concrete patch kit that is available in 1 gallon containers or larger. This type of product is an excellent choice for deeper and larger width cracks that span a long length of the garage floor.
These usually consist of a 100% solids epoxy gel that has a sand aggregate that you can mix in as a filler. Once you apply it to the crack it can be troweled smooth with a concrete float. One of our favorites that we recently reviewed is Xtreme Set 100 by Legacy Industrial.
You will not find product like this at a home improvement center either. Instead, they are much more common in the professional floor coating industry and will need to be purchased online in most cases. You can find a good example of such kits from Legacy Industrial or this one from EpoxyMaster.
Repairing Cracks in Your Garage Floor
The first thing you need to do when making a crack repair is to chase the crack. This is the process of using a hammer and cold chisel to break way any loose edges or material within the crack. The repair is only as strong as the material it adheres to.
If you don’t have a cold chisel, you can easily find them at your local home improvement center or purchase them online from Amazon
Chase the crack by placing your cold chisel at an angle that runs in line with the crack. Firmly hit it with a large hammer or small hand held sledge hammer. The chisel will break away any loose material as you hit it with the hammer. Continue in this fashion until you have chased the entire crack.
Use a shop vac to clean out the loose debris and then scrub the crack well with a stiff wire brush. This will remove any weak laitance and prep the surface for the repair material. Vacuum out the crack again and then you are ready to apply your repair.
Be sure to follow the directions carefully for the product that you use. If you use a 2-part epoxy gel or 2-part epoxy sand slurry, work it good into the crack in order to push out any trapped air. Once it’s worked in, trowel it as smooth as you can before the material begins to set up. Watch for any low spots that may need additional repair material added.
If you are using the Simpson Strong-Tie or similar product for larger cracks, it works best to fill 3/4 of the crack with silica sand first. Apply the Simpson Strong-Tie over the sand up to the top of the concrete. Allow a couple minutes for it to soak in and then apply it again to fill in the low spots.
Once you do that, apply more sand loosely over the repair and let it set for 20 minutes. After it has set, you can scrape off the top layer with a paint scraper or putty knife.
Once the repair has cured, you can grind it flush to create an even transition if you will be applying paint or an epoxy coating. This will prevent most repairs from telegraphing through the coating and you will not see them.
Contrary to some information out there, you do not need to chisel cracks to form an inverted or backward-angled cut. This is only required of large repairs that are made using concrete or a cement based patch.
Since new concrete does not adhere well to previously cured concrete, the backward-angled cut helps to keep the material from lifting out. Epoxy, polyurethane, and polyurea crack repair products on the other hand form a tenacious bond to properly prepared concrete and do not need an inverted cut to stay in place.
Another process which works well for chasing cracks is to use a small 4″ angle grinder with a crack chasing masonry wheel. The wheel is tapered to form a nice clean groove in the concrete. You can see how it works in the video below.
Chasing a crack with 4″ angle grinder and a crack chasing wheel
When repairing deep cracks, it’s best to fill the crack part way with silica sand. This will prevent the repair material from seeping down deep into the concrete and settling. It saves you from using excess material as well as creating low spots that need to be refilled.
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 of contraction joints or where the concrete 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 use an epoxy sand slurry or a polymer-modified cement topping or patching mix. Which type you use depends on the extent of the repair. It requires a little more effort that repairing a crack, but it’s not that hard to do.
After the surface has been prepared properly, you 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 it cure according to the instructions. You may need an additional application to fill in any small divots or low spots you missed.
You should end up with a nicely repaired surface that won’t be noticeable once it is painted or epoxied over. We cover this in more detail in our article on how to repair spalled or pitted concrete.
One thing to be aware of if you are planning on applying a clear coat sealer to your 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.
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 or epoxy slurry to fill in those low spots. 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.
I patched some cracks with 5 minute epoxy from Loctite (100% solids I believe). Unfortunately I forgot to sand the patches before applying the base coat, and the patched areas were much more glossy than the rest of the floor, which matted out from the porous concrete. I figured this would go away after applying a clear glaze coat, but the patched areas are still more glossy than the rest of the floor and the glaze coat continued to matte out on the non-patched areas. I’m thinking a thorough sanding of those spots and another coat may help, what do you think?
No, it won’t help Michael. What you needed to do was apply another color coat to even out the look. We are assuming the product you used was not a real thick high solids epoxy. As a result the color coat acted like a primer and did as you said. A second application of the color coat would have created a much more consistent color tone and gloss. A clear coat is not the answer to fix such an issue. A clear coat is exactly as stated – it’s clear. So any color and tone inconsistencies that you have will still remain. In some cases they can be highlighted even more by the clear.
You mentioned a clear glaze coat. One of the few manufactures to use that terminology is H&C products. If that what you used, their glaze coat is actually an acrylic sealer and not an epoxy. You would have to completely remove the glaze coat by sanding down to the color coat in order to apply a second coat of color. Epoxy cannot be applied over acrylic coatings.
We just purchased a home with a really nice epoxy garage floor in the garage. The finish is great but there are separation cracks in the contraction joints… nothing outrageous but for me and my obsession with looks it bothers me. Any suggestions on how to fill these cracks?
Contraction joints are created to induce cracking within the joints and not across the surface Navarone. If the joints were filled and then coated over, there is always a risk that cracking will eventually telegraph through the coating. Repairs to epoxy stand out and the cracks will only come back. If the joints were not filled and you can see cracks at the bottom of the joint where the concrete is, you do have one option. You can fill the joints with a gray self-leveling polyurethane joint sealant such as SikaFlex. These type of joint sealants have high elongation rates and will move with the joint and will not crack. It will, however, change the look of your floor since the sealer will divide the look of your garage floor into separate sections.
I have low area in my concrete carport floor that causes water to stand at my door. the lowest area is about a 1/4 of an inch. what would you recommend to level the floor? What do you recommend coating the rest of the carport to get the color the match?
We have an article about fixing low spots here, Anthony. The typical type of coatings you may be familiar with are generally not recommend for outdoor use. They can amber (turn yellow) and be very slippery in certain weather if a proper anti-slip is not applied in the final coat. What many companies do for carports and drives is to apply a micro topping or overlay. This will cover all repairs and provide brand new surface to work with. They can be left bare or stained and sealed with an acrylic sealer.
This video here is an example of a driveway that was repaired and resurfaced with a micro topping. Sakrete has a video of their product being used on a patio.
What would be your definition of a “hairline” crack? I have one that goes basically the width of my garage that is not wide enough to fit a coin in. I would like to make sure I don’t need to chase that crack and repair it or if it is a safer bet to just chase it and then fill it in with some leftover Rust-Oleum’s EpoxyShield Concrete Patch (mentioned above). Please let me know. Thank you much
A hairline crack would be something you couldn’t fit a business card in. Even then filling them depends on what type of coating you are using. If it’s a low solids home improvement epoxy kit, EpoxyShield for example, then you may still run a chance of seeing the crack. Higher solids coatings do a better job of filling these cracks since you get less material shrinkage from water or solvents evaporating from the coating as it cures. If ever in doubt, it’s best to chase it and fill it. The EpoxyShield concrete patch works fine for that.
Thanks- i’m worried that since i would be chasing the crack the entire width of the garage, that after i fill it and sand flush that it would show through the epoxy coat – using rustoleum’s “professional” solvent based kit (light gray). thank you sir for the guidance
The Rust-Oleum Professional is much better choice of the water based kits Thomas. It cures slightly thicker, has more abrasion resistance, and adheres better. You shouldn’t see the repair if it’s ground or sanded flush with the concrete. It’s the same process that a wood worker does when filling holes or an auto body shop does on a fender. Also, the more color flakes you have on the floor, the less you notice imperfections.
I have a hole in my garage floor approx. 180mm long x 90mm wide, 20mm deep at the driveway end back to nothing. the garage floor is painted with a floor paint fro Bunnings that has a flake spread over it after painting. This hole has been repaired twice with the patch breaking up after 2 weeks. The patch is where the car runs over it. I am looking for something to fill and repair this patch and recoat the floor with the Bunning floor coat after.
Hello Terry. We are not familiar with the name brand products you have available in Oz. However, a 100% solids epoxy mixed at a ratio of 1 part epoxy to 3 parts clean sand will make for a repair that is stronger than concrete. Mix the epoxy first and then quickly add the sand to the mix. Once mixed, press it in the hole good with a margin trowel to avoid air pockets and then spread it evenly. Grind it flush after it cures before you paint over it. Just make sure that all the loose debris and dust is cleaned out of the hole first.
HELP!! We had our garage floor done last week with an epoxy finish. The contractors filled cracks but left other visibly damaged spots. Now the epoxy finish is done and we now have to figure out how to repair the floor and start over. Any help and information would be greatly appreciated!!
Hello Tammy. I’m assuming these weren’t actual floor coating contractors then. Painters or a general contractor maybe? You didn’t state specifically what is wrong or what specific type of product was used, however, it generally requires making the needed repairs and then recoating the entire floor to get things right.
We have several long cracks in out garage and one good size section about 5×3″ were the rebar is actually showing. We also have a quit large low spot by the garage back door that fills up with melted ice coming off the car in winter. We are both handicapped and would like suggestions on the easiest and best way to repair looking forward to your suggestions
Honestly Carolyn, we would recommend that you hire the job out to a concrete specialist or concrete flooring contractor. Making repairs like that requires labor that puts you on your hands and knees as well as using some hand tools. It may be too much for a person with a handicap to tackle.
If I have cracks running through spalled and pitted areas, should I chase and fill the cracks first then cover the area with a patching mix, or vice versa?
You will want to chase and fill the cracks first, Gary, after you prep the area and remove all the soft and loose concrete. Use the patching compound for the pitted and spalled areas after that.
The corner of my garage has settled (I believe) to where there is about a 3/4” difference between the garage floor and the driveway. During heavy rain, water sometimes comes through the small gap between the garage door weather stripping and the garage floor. My plan was to use epoxy slurry or a self leveling compound to fill that low spot on the floor, does that sound like it will work?
When filling a low spot of that size (about 3/4”) can that be done on one coating or should I do two coats in that area?
Hello David. You will want to use polymer-modified concrete to fill in your area. An epoxy slurry would be very expensive for a 3/4″ depth. Do not use the self-leveling underlayment that you can find at your local home improvement centers. It is not strong enough and it is not designed as a wearable surface.
I’ve got a garage floor where someone has attempted to patch cracks and low spots with a self leveling compound, and then installed carpet on top with a tough latex adhesive. I’ve gotten the carpet removed, and given a shot at scraping the adhesive (which at best leaves a light visible residue) and is well nigh impossible to get off the patched areas. Do you have any suggestions on how to get this back to being a functional garage floor?
What you need to do, Ren, is grind the garage floor. This will remove the glue residue and smooth out the patched areas. A more aggressive grinder like the 10″ Edco unit works better at smoothing out patched areas. Hopefully an actual polymer-modified concrete patch repair was used and not a self-leveling underlayment for wood flooring, carpet, tile, and etc. Underlayments are not formulated as a wear surface.
Will polyurea/polyaspartic coatings stick to an epoxy crack repair product like the Simpson strong-tie or rustoleum epoxyshield crack repair?
Yes it will, Daniel. Just make sure to rough up the repair with 100 grit sandpaper if you didn’t grind it.
I just bought a SoCal house that was built in 1988, it’s time to give this garage the attention it’s been deserving! After reading your articles, I could use some advice on making sure my workflow is chronologically correct below?
1.) Finish dry-walling exposed areas, then texture/primer/paint
2.) Patch any cracks/pitting/small missing chunks in concrete
3.) Clean the garage floor, including the degreasing steps
4.) Acid etching
5.) Apply top coat (epoxy, etc.)
Could I potentially tackle the drywall piece after I’ve finished with the floor? Theoretically, I could wipe up whatever mess I’ve made off the epoxy, no?
Thanks again!
Your workflow is fine, Matthew. Ideally you want to do the floors last, but as long as you throw down some drop clothes you can always do the drywall after the floor. Paint is hard to remove from a coating without causing it to loose gloss so you want to be careful. Coatings are easy to clean, but they aren’t like Teflon where nothing sticks either.
Hi Shea,
Thanks for your response to my question yesterday. I am using a 2 part self mixing epoxy from a company called SIKA, it’s called Pro Crack Fix. Are you familiar with this? Its a clear free flowing liquid used with a caulking gun. My cracks are fairly large and are using a lot of the material. Can I fill with sand like the Simpson product you talk about to use less product?
Also I assume I can grind this down after to make it flush with the concrete? I am using Epoxymaster coating will there be any problem fir coating to adhere to the SIKA?
Thanks again,
You can fill the cracks partially with sand if they are deep, Rob. You still need enough material to provide strength. Don’t use sand in shallow cracks. If the product is somewhat runny, you can mix sand with the product when filling the cracks. This is better since the sand acts as a filler and bonds with the epoxy at the same time. Grind them all even with the surrounding concrete after they cure and you will have no issues applying a coating.