We’ve all seem them. Those annoying puddles of water that collect in the low spots of your garage floor soon after you have pulled your car in from the rain or snow. Some are shallow enough that the water will evaporate in a few hours or so, but it seems the deeper ones can linger long enough to start breeding mosquitoes if you didn’t mop it up or push the water out the door.
If you are going to paint, seal, or apply an epoxy coating, then one of the first things you will want to do is try to level-out these unusually low areas of your garage floor before you start. Even if you aren’t planning a garage flooring upgrade, these low spots can create a safety hazard when they puddle or can cause damage to the concrete if you live in a cold winter climate.
Why your garage floor is not flat and level
Before you get too excited about these uneven areas of your floor, the first thing you should know is that garage floors are rarely level or flat without the occasional low spot, high spot, or raised edges that trap water. Most of these spots are acceptable but sometimes you get low spots that are just too deep or too large to ignore.
Part of the reason for this is that garage floors are not always given the same close attention by builders as other areas of the home that require the floor to be as flat and level as possible. They are usually finished by hand and are rarely machine or hard trowelled. Bad lighting when finishing, poorly set forms, overly wet concrete, and poor finishing techniques can all contribute to low spots in your garage floor.
Depending on what area of the country you live in and whether you have a basement or not, some building codes require that garage floors meet a minimum pitch toward the garage door. This is to facilitate drainage or to allow for noxious, heavier than air gasses to flow out the garage door. This can make it more difficult to get the concrete flat (not level) if the finisher is not paying close attention.
Drains are another consideration. If you have a drain in your garage floor, then the floor can’t be level at all since the slope of the floor has to pitch towards the drain. The slope can be flat though. Nothing is more frustrating however when you have areas that puddle and don’t flow toward the drain.
And then finally, there is the issue of the floor being nice and level. What??
Think about it. Concrete floors need a minimum pitch of 1/8” to 1/4″ per foot (depending on finish) to allow water to flow. That is a minimum 2.5″ – 5″ drop over 20 feet. If your garage floor is nice and level, the water will just puddle and not go anywhere, sometimes making an area of your garage seem like a low spot when it actually isn’t.
Garage floor repairs are never fun, but the good news is that many of these low spots can easily be fixed with a little bit of work. The type of repair you make may depend on the size of the area, that type of flooring you want to install, or what the actual cause of the low spot may be.
mark the low areas of your garage floor
The first thing you want to do is to identify the low spots that need to be fixed. You probably already know the general area.
The easiest method is to flood these areas of the floor with some water and then outline the low spots with some chalk once most of the water has drained or settled. The other method is to place a straight edge or long level across the suspected areas of the floor to identify and chalk the low spots.
One important bit of information you need to investigate is where this water will go once the low spot is made level to the surrounding area. You don’t want to be chasing a puddle of water all around your garage floor because you did not take this into consideration. It should be moving towards the garage door, a contraction joint, or a drain.
Repairing the low spots
Fortunately most low spots are not very large and not as deep as you think – usually less than 1/4″. For these areas we like to use an epoxy slurry for the repair. This is a mixture of 100% epoxy with a silica sand aggregate. This is the same type of product used to repair pitting and spalling.
This type of repair is extremely strong (stronger than the concrete) and ideal if you are going to paint, epoxy coat, or cover your garage floor afterwards. The sand acts as a filler and gives the epoxy the ability to be troweled smooth with a cement float. You can see an example of such a product here.
This is a small example of an epoxy sand slurry used to repair pitting in a garage floor. When mixed in larger quantities it works very well to fill and level low spots as well.
The areas to be fixed need to be clean and dry, free of all oil stains, waxes, or sealers. Prep the surface by grinding or sanding with 40 grit sandpaper. If you aren’t sure about what type of grinder to use, you can get more info about 4″ angle grinders and the proper concrete grinding wheels here.
An orbital sander is handy if you don’t have the proper grinder. Sanding will only work for this as long as there isn’t a sealer or other coating on the concrete. They will not work to sand a repair flush however. If you are going to prep your garage floor for a coating by acid etching, then do that first before making the repair as it will prep the concrete for you.
Follow the mixing instructions of the epoxy patch repair material. Once it is mixed, you need to start working as you will only have 20 – 30 minutes of working time.
Dump the repair material onto the low spot and start troweling it in using firm pressure. Once it is spread out over the area begin troweling it smooth with a cement float. You can achieve a nice, clean finish if you wipe the blade of your float with Windex or acetone before the final passes. Use a straight edge or level to check your work.
After the repaired area has cured for 24 hours, you can finish prepping the repaired area by grinding the surface and the edges to make for a smooth and even transition.
For low spots that cover larger areas of the floor, such as a 5’x5’ area in a corner for example, we like to use a polymer-modified cement topping. These are self-leveling and adhere very well to concrete. They consist of a mixture of Portland cement, sand aggregate, and polymers. You just add water.
The nice thing about using polymer-modified cement is that it will accept a sealer, stains, and coatings after it has cured.
The chemicals in the polymers of the cement help act as a bonding agent. Never use regular cement mix. It will not adhere well to the concrete and will break apart because it will not meet the compressive strength required for shallow fills and feathering edges.
Polymer-modified self-leveling cement being used for a garage remodel
You can find most self-leveling toppings from concrete construction supply stores. Your local home improvement center usually is not the best source for this. An example of such a product would be Ardex K-301 self-leveling concrete or MG-Krete self-leveling concrete. Just contact the manufacturer to find the nearest distributor or visit your local concrete construction supply store to see what product they have on hand.
Do not use self-leveling cement designated for use as an underlayment or indoor use only. They are not as strong, they will fail in freeze/thaw conditions and they wear quickly since the surface is not designed for traffic. If in doubt, contact the manufacturer.
Pay close attention to the surface prep instructions. Some product just requires a clean surface while others may require that it be profiled similar to the epoxy repair. Others may require the use of a primer. Don’t worry however as the process is very straight forward and not hard to follow.
Once your surface is prepped properly and the repair material mixed, slowly pour it out onto the floor. It will naturally fill in the lowest part first and then work its way toward the edges of your low area. Be careful not to let it run far past your chalked borders.
The material does a good job of lying flat on its own. Use a trowel or cement float to feather the edges to the garage floor. Once it has cured for an hour or so, you can take heavy grit sandpaper to any raised edges or lines that were created from the trowel or float.
Once it has cured for 24 hours you can grind the surface for the proper profile if you are going to be applying a garage floor coating.
It’s important not to let the repair material cover up any contraction or expansion joints. If it does get in one of these joints, it easiest to clean out with a putty knife or flat bladed screwdriver about 20 to 30 minutes after it has begun to set up.
Raised edges that create low spots
Believe it or not, you could have a fairly flat garage floor that traps water and creates the illusion of low spots. This is most common if you have larger “V” shaped contraction joints in your garage floor that were created via hand trowelling. It can also happen with saw cut joints as well but is usually not as predominant.
What happens is the surface of the concrete can contract more than the rest of the slab if it was allowed to cure or dry much quicker. As a result of this contraction, the surface pulls at the edges of the concrete and causes these joints to curl up. These curled up edges then create a nice dam that can trap water instead of letting it flow into the joint.
The easiest way to correct for this is to grind these raised edges flat to the rest of the concrete. This will effectively remove the dam and allow water to move into the contraction joints.
Final thoughts
These methods for fixing low spots in your garage floor are extremely effective. We recommend though that you don’t get overly concerned with chasing down every spot you can find. The water has to go somewhere and if you have a fairly level garage floor then you will be chasing your tail.
Remember that garage floors are not perfect and rarely completely flat. It’s normal to have the occasional few spots that will puddle slightly when water is introduced. However, if you have large areas or deep spots that puddle and do not evaporate within a day, it will benefit the life of your garage floor as well as your safety to have these low spots fixed.
If I am going to use the Diamabrush concrete prep tool to prep the floor, do I still need to clean the old (set in) oil and grease spots? To be clear, there is no wet oil or grease residue on the surface, it is all set in.
Wouldn’t the Diamabrush scrape it all away?
Thanks
Hi Steve. Oil penetrates the concrete surface and acts as a barrier. How far it penetrates depends on how porous the concrete was initially and how long it has sat. It’s best to draw out all the oil you can first before you grind. You won’t hurt anything if you don’t do that first, but it may require cleaning the spot after grinding and then grinding over the spot again. Just make sure it passes the water drop test before you apply any patch repair or coating.
The Ardex representative recommended to install ARDEX K 301 from 1/4” to 3/4”. To feather the edges his recommendation is to saw cut 1/4” deep at the edge and back chip the existing concrete. What is your experience of feathering the edges?
Hello Bill and great question. It depends really on the product, the edge, what the manufacturer states and what treatment, if any, is going over it. We found that if the floor being repaired is going to receive a high solids, high build coating, then feathering out with a trowel along with some light grinding afterwards is all that is needed. The repair will not telegraph through high build coatings.
However, if Ardex is recommending to saw cut the edges for the K301 then we recommend following their instructions. It’s not difficult to do and will provide for a solid edge that can be ground flush.
I recently poured a patio slab for a customer and have an issue with a small birdbath and heavy broom marks through out the surface ( concrete was poured in 100 degree weather which didn’t help). The owner wants the birdbath fixed (2’X2′ area) and now a smoother surface in lieu of the existing broom finish. What do you recommend to repair the birdbath and refinish the surface? Thanks in advance
If you want to repair a low spot in a patio Luke, then you would definitely need to resurface the entire patio or the repair would stand out. You may want to offer the option to lightly grind the entire surface to create a smoother finish and then apply a good penetrating sealer to protect the concrete instead. Water may puddle in the bird bath, but the sealer will protect the concrete for years to come.
If that isn’t an option, then you will want to fill the low spot with a polymer modified cement if it’s deep. If not deep, then a resurfacer may fill the low spot on it’s own if applied correctly. We recommend contacting Ardex about using either Ardex K-301 or Ardex CD. Both can be troweled to a smooth finish and doesn’t require extensive concrete prep before application. They provide an example video here of how the Ardex CD is applied.
So after pouring a self levelling concrete you should still grind if you are applying an epoxy or polyaspartic overtop?
Or is it ok to go without the grinding since it is a polymer modified cement and is more receptive to other coatings?
Or, Perhaps a primer would suffice? If so, what type?
Having a hard time finding any solid info on this, would appreciate some info/advice.
It’s a good question Trevor. You need to grind the surface to accept a coating because you can’t acid etch polymer-modified cement. The surface is treated just like regular concrete in regards to coating.
Well…. I guess this will be a test to see how long it holds up without the grinded surface since I already did 2 small rooms. It is just in the basement with foot traffic so I’m hoping it’ll hold up.
I did test grind a very small patch and it didn’t seem to open the pours or remove any kind of latence or change the surface at all like grinding does on concrete.
Hopefully it will hold Trevor. There isn’t laitance with polymer-modified concrete and the grinding does not open pores like it does for concrete. What it does is profile the surface to provide bite for the coating.
That does make sense…
if just profiling the surface of the self leveller is the goal, can you suggest an alternative or easier way to do this other than getting a big floor grinder? The levelling compound seems much easier to scuff and profile than hardened concrete.
Would you also recommend a primer be used on the profiled surface to ensure a better bond ? If so, what type? Just whatever primer is recommended for the coating product being used?
Thanks for all your advice so far.
Polymer-modified cement should cure extremely hard Trevor – a minimum of 4,000 – 5,000 PSI. It is actually stronger than regular concrete and just as hard. Hopefully you didn’t use a self-leveling underlayment which many of the home improvement centers sell. Underlayments are not intended for coatings (though they may bond OK) or to be used as a wear surface. They are designed to have tile, carpet, wood flooring, and etc installed over them. If this is what you used, you may want to contact the manufacturer about possible issues. The good news is that if did use this, you didn’t use it in a garage that will see vehicle traffic. You may be able to rough up the surface with 40 – 60 grit sandpaper on a pole sander or orbital sander instead of grinding.
Regarding primers, you didn’t state what type coating exactly that you were using. Primers are recommended for very high solids or 100% solids coatings. Lower solids coating generally do not require a primer. Sometimes it works best though to use two coats. The first acts as a primer (the ugly coat) and the second coat is the finish coat.
We have an attached garage and the garage floor is holding water across most of the front wall (opposite the garage door) and also along the outside wall up to 3 feet out. There is not a floor drain. There are also areas up to 5″ x 5″ that have chipped or pitted away in other areas of the floor. Can the polymer material be used over the entire floor as long as the expansion joints are scraped out?
Yes it can Kathy. Just keep in mind that the floor can still eventually be damaged by that much moisture if the slab does not have a moisture barrier and the walls are not sealed from the outside or have some sort of drainage system.
Can you suggest a contractor in Lansing, MI area who can do this job
Thank you
Hello Pete. We don’t know of anyone in Michigan. However, you may want to contact EpoxyMaster. They are based in Michigan and may be able to help you with finding someone reputable.
I need to level areas of my unattached 24×36 garage. It has been insulated and heat installed. When we purchased the property in February the building had a 10′ wide overhead door which we replaced with a 16′ door. The original 10′ wide area is lower than the remainder on both sides of the 16′ door and a lot of water is finding the low areas of the garage! We installed an extra thick seal on the bottom of the door but no help. The apron is also a bit higher than the 10′ wide area of garage floor. It seems the concrete leveling compounds in my area stores are not what you recommend. We have all the big box stores, but all I can find is “Interior” underlayment leveling compounds. I asked employees there but they don’t have an answer? Where do I find “Exterior” concrete Leveling Compound? Thanks!
Hello Bob. Yes, sometimes this type of product can be difficult to find if you are not a contractor. What we suggest is contacting the manufacture’s themselves and ask where you can find their product in your area. They all have toll free customer service phone numbers and some have a page to find local distributors in your area. If you tell them about your project, some of these manufactures will offer tips and recommend which product would work best. Mg Krete, Ardex, and Euclid are examples.
My garage floor has a low spot in the front corner, leaving a gap between the driveway and garage floor of almost 1” height difference. During heavy rains, water will enter underneath the garage door in that low corner. (Currently I just place a towel next to the door to stop the water from coming in).
Will using a polymer modified cement work to level the garage floor in that area and eliminate the height difference between the garage floor and driveway? Anything else I would need to take into consideration? Thank you!
Hi David. Yes, it should level it out if it’s that simple and applied correctly. Don’t forget to take into consideration where the cement will butt up against the foundation/wall. Also, make sure that the product you purchase can be poured at that thickness. It may take two applications. Finally, do not confuse the proper product with floor leveling underlayment that can be purchased from the home improvement stores. It is made to have tile, carpet, wood flooring, and etc. installed over it. If it says underlayment, it’s not the right product.
I have pretty bad build up of water run off in one corner of my garage and it is starting to ruin the walls. It is just concrete with no sealers or anything which it will probably stay this way for quite a while yet if not indefinite.
What would you recommend to stop this water build up preferably something that will blend in with the concrete floor and that doesn’t need to be coated with anything afterwards?
Thanks for any help and advice!
Hello Kyle. You would need to use a polymer-modified concrete skim coat or patch depending on how low the corner is. No matter what product you use, the repair will stand out and will not “blend” with the rest of the floor. It will be obvious. The only way to conceal it would require a proper floor coating. If you do decided to repair the low area, make sure that the water it displaces is going to be going where you want it.
I’m planning on adding ceramic/porcelain tile to my garage with a good amount of low/high spots. I plan on using self leveling compound but worried it won’t settle to the existing slope. Is there a technique to help it stay in the slope of the garage? Do you recommend a different product? The low spots range from 1/8 to 3/4 and maybe 1 inch.
Hello Eli. It actually takes a good slope for a self-leveling compound to run all to one side. Even on a flat surface, self-leveling products don’t automatically level on their own without being manipulated and the edges troweled. We recommend mixing with a little less water so that it is not too soupy. Pour it out and then use a large trowel to start filling in the areas and smoothing the surface out. A large straight edge works well for checking your work. LevelQuick RS by Custom is a good underlayment to use for this situation. It sets fast so you don’t have to worry about relative level changing while is cures. Plus, it has a rating of over 4000 PSI. This is important since it will be supporting a car and not just foot traffic.
Just a note for everyone else who may read this… Underlayment self-levelers are OK to use if you plan on tiling the floor. Do not use it if you plan on coating, painting, or sealing the floor. It is not compatible for that type of use and is not considered a wear surface.
I have a piece of a slab that cracked off and sank about 1/4″ to 1/2″ below the rest of the garage floor. I have not measured the exact depth yet.
The piece of slab is triangle size. 3 ft by 7 feet with a hypotenuse of about ~7.7.
I read in your other article that sunk slabs is a costly repair that is not an easy fix and should be done by a professional.
I’m wondering if…
1) there is a chance that my epoxy base coat will cover this up when applied
or
2) I can get away with using Ardex K-301 over the cracked slab to level the floor.
Any other suggestions would be great.
No Jeff, your epoxy base coat will not cover that up. To put it in perspective, a multiple coat commercial epoxy flooring system runs an average of 40 mils thick. That’s .04 inches or less than 3/64″. If you have had that large a piece of slab break and sink that deep, you may have other issues going on with the foundation under the slab that you are not aware of. While you could technically fill that area with Ardex, there is no guarantee that it will not sink any further or that another piece may break off. We would suggest having a professional assess what is going on with your slab before you proceed further.
I have an attached 2 car garage that has water pooling in 2 spots – both about 0.75 to 1 inch deep and approximately 3 ft by 3 ft. I plan to epoxy coat the garage. Would it be okay to use self-leveling concrete to fix the leveling issues? And if so, should I grind or acid etch the new concrete layer before I apply the epoxy coating?
Hello Adlai. 1″ is fairly deep for a low spot. Providing that the area is not too large, we would recommend using an epoxy/sand slurry to fill the low spots. These work great because they bond very well to the concrete and can be feathered down fairly well without worry of it delaminating at the edges. Since you need to grind these areas flush after they are filled, grinding the entire floor is the recommended method for the floor prep and repairs.