We’ve all seen them. Those annoying puddles of water that collect in low spots of your garage floor. They typically form when you hose out the garage or after you have pulled your car in and out a few times on a rainy week. Most are shallow enough that the water can evaporate in a few hours or so. However, it seems the deeper ones can linger long enough to start breeding mosquitoes if you don’t push the water out the door.
Examples of more serious low areas can be the sides, corners, or back end of a garage floor. They can collect large volumes of water from being lower than the rest of the slab. This is the type of concrete floor repair that needs careful consideration.
Low spots or depressions in the middle of a garage floor can be a nuisance as well. However, we don’t always recommend trying to fix them unless they are unusually deep. We will discuss this in more detail shortly.
If you plan to seal the concrete, apply a floor coating, or some other garage flooring option, then you most likely will want to explore the options of leveling unusually low areas before you start.
Even if you aren’t planning a flooring upgrade, deep low spots can cause efflorescence from constantly being wet. They can even discolor the concrete from water sitting for long periods.
Fixing low areas of the garage floor is never fun. However, the good news is that it oftentimes can be done. It just requires a bit of work and the right materials. What materials you use may depend on what you plan to do with the floor.
So let’s look at what causes low areas of the garage floor, determine if they should be repaired or not, and what materials are required to fix them.
Why your garage floor is not flat and level
Before you get too aggravated about these uneven areas of your floor, the first thing you should know is that garage floors are rarely level or flat. It’s very common to have the occasional low spot, high spot, or raised edges that trap water.
Most of these spots are acceptable and just an annoyance. However, sometimes you can have a low spot that is just too deep or too large to ignore.
Garage floor slabs are typically placed separately from the rest of the foundation. As a result, they are not always given or demand 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 rarely machine-troweled due to the extra expense.
In addition, bad lighting when finishing, poorly set forms, overly wet concrete, and poor finishing techniques can all contribute to low spots.
Depending on what area of the country you live in, some building codes require that garage floors meet a minimum slope pitch toward the garage door. This is particularly true for homes with basements that may be underneath.
The slope is required 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), particularly if the finishers are not paying close attention.
Drains are another consideration. If you have a drain in your floor, then the surface can’t be very flat since the slope of the floor has to pitch towards the drain. However, it can be frustrating when you have areas that form deep puddles and don’t flow toward the drain.
And then there is the issue of the floor being fairly level and flat. What??
Think about it. Concrete floors need a minimum pitch of 1/8” to 1/4″ per foot for water to flow across the surface on its own. The amount of pitch is dependent on how smooth the concrete is. That works out to a minimum 2.5″ – 5″ drop over 20 feet.
If your garage floor is reasonably flat and level, the water can’t move and doesn’t have anywhere to go. It will tend to puddle anywhere it can and just sit there. Any slight depression on the surface will create the illusion of low spots on your garage floor when there really isn’t any concern.
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Measure and Determine If Low Spots Need To Be Filled
The first thing you need to do is outline the boundaries and measure the depth of the low spots that you believe need to be fixed. Knowing the depth and area will also help to determine how much repair material will be needed.
If you are not sure where the boundaries of the low spots are you can use a straight edge to find them. You can also flood these areas of the floor with some water. Once most of the water has drained and settled, outline the boundaries with a concrete crayon marker.
Markers such as these require a little bit of effort to remove. You don’t want them erased from walking on them. We recommend something like this one from Amazon.
Remove any water that was used once marked. Next, place a straight edge over the low spot from boundary edge to edge. This will allow you to measure how deep the depression is.
For low areas in corners, sides, and back of the garage floor, we recommend placing a long level or straight edge from the boundary edge to the wall. This will help you to determine the depth as well as how far up the wall you will need to go with repair material.
If you don’t have a straight edge that is long enough, then we recommend using a string. Have someone hold the string at the boundary edge and then pull it tight to the wall. You can hold a level to the top of the string as you move it up and down the wall to find level and mark it.
We recommend that you consider filling any low spots in corners, sides, and back of the garage where water sits up against a stem wall, concrete block, or some other structure such as wood.
However, we don’t always recommend filling other areas in the middle of the garage floor unless they are greater than 3/16 of an inch deep. Particularly if you don’t plan on covering the repair with a floor coating or some other flooring option.
The expense and effort are not always worth it. More importantly, if not covering it up, the repair is going to stick out like a sore thumb and be very obvious. You cannot make a concrete repair blend with the rest of the floor no matter what type of material you use.
In addition, it’s important to investigate where this water will go once the low spot is made fairly level respective to the surrounding area. You don’t want to be chasing a puddle of water all around your garage floor because you did not consider this.
If water does move, it should be moving toward the garage door, a contraction joint, or a drain. Not just the next lowest spot on the floor.
Raised edges that create low spots
You could have a fairly flat garage floor that traps water and creates the illusion of low spots. This is most common near the troweled edges of the concrete slab and deep “V” shaped contraction joints.
The reason for this is that concrete shrinks as it cures. This happens when water from the concrete mix evaporates from the slab during the curing process.
The surface of a slab will cure faster than the rest of the concrete if not properly covered or kept damp. When the surface cures faster, it will contract at a rate greater and earlier than the rest of the slab.
As a result of this contraction, the surface pulls at the edges of the concrete and troweled joints causing them to curl up slightly. These curled edges then create a dam of sorts that can trap water instead of letting it flow into the joint or out the garage door.
Attempting to fill in low areas caused by concrete edge curling is problematic. The best option if this appears to be the issue is to grind these edges flush with the rest of the floor. This has solved more than one low spot problem.
We have an article here about concrete grinding. We recommend using a 4″ or 7″ angle grinder with a concrete turbo cup wheel to grind such areas.
Repairing And Filling Low Areas Of The Garage Floor
Fortunately, most low spots in the middle of a floor are not too large or deep. They are 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.
Epoxy slurry fills and repairs are extremely strong. The sand acts as a filler and provides the ability for the epoxy to be troweled smooth with a cement float. It is ideal if you are going to paint, epoxy coat, or cover your garage floor afterward. In addition, it acts as a sealer and is freeze-thaw resistant.
You can see an example of such a product here at Legacy Industrial.
This is an example of an epoxy sand slurry used for a smaller repair. When mixed in larger quantities it works very well to fill and level low spots as well.
The areas to be filled and leveled need to be clean and dry, free of all oil stains, waxes, or sealers. Prep the surface by grinding or etching. It will not adhere well if this step is not followed. If grinding, you can use the same type of grinder we mentioned above for raised concrete edges.
Follow the mixing instructions for the epoxy patch repair material. You should use less sand for workable self-leveling properties and mix only that which you need. You can use the depth and total area of the low spot to determine how much material you will need.
Once mixed, immediately begin the application. You will only have approximately 20 – 30 minutes of working time.
Dump the repair material onto the low spot and apply it with firm pressure. Once it is spread out over the area you can begin troweling it smooth with a cement float. You can achieve a 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 a minimum of 12 hours, you can finish prepping the repaired area if you will be applying a floor coating. This will require that you grind the surface and edges to make an even transition.
As good as epoxy slurry is, it can get expensive fast for large areas. Plus, it doesn’t self-level on its own.
For low spots deeper than 1/4″ and larger than 15ft², we recommend using a polymer-modified cement topping. They consist of a mixture of Portland cement, sand aggregate, and polymers. You just add water.
These are self-leveling and adhere very well to concrete. The chemicals in the polymers of the cement help to act as a bonding agent. They are just as strong, if not stronger than most concrete. This article explains more about how they work.
In addition, polymer-modified cement toppings and fillers will accept paint, most stains (except acid stain), and coatings after it has cured. However, they will not accept penetrating sealers. We have more information about the different types of sealers here.
Never use regular cement mix. It will not adhere well to the concrete. In addition, it will break apart because it will not meet the compressive strength required for shallow fills and feathering edges.
You can find most self-leveling toppings and fillers from construction and concrete supply stores. Your local home improvement center is not the best source for this. An example of brands we recommend are Ardex self-leveling concrete, MG-Krete self-leveling concrete, and Sika
Contact the manufacturer to find a distributor near you. In addition, talk with tech or customer service to help determine which type will be best for your project.
Do not use self-leveling cement underlayments! They are not as strong, they will fail in freeze/thaw conditions and they wear quickly since the surface is not designed for traffic. These are less expensive and typically found at home improvement centers. 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. Regardless, the process for application is very straightforward 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 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. 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 a joint, the easiest way to remove it is to use a putty knife or flat-bladed screwdriver about 20 to 30 minutes after it has begun to set up.
Final thoughts
These methods for fixing low spots in your garage floor are extremely effective. However, we recommend 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 are 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 your garage floor, your safety, and your sanity to have these low spots fixed.
Molly says
Have a 30×60 shop. Concrete slab has multiple low spots 1/8″ to 1/4″. Plan on quartz epoxy coating. Best suggestion to level concrete ?
Thanks.
Shea says
Hello Molly. Quartz epoxy coatings require multiple coats of 100% solids epoxy. Most low spots like that are naturally filled when using a gage rake unless they cover a wide area. If you want to fill the low spots first, then we would recommend using a 100% epoxy sand slurry.
Molly says
Thanks for your reply. Yes the areas are quite large and pool water. This will be a double broadcast quartz with epoxy topcoat.
Thanks
Robert La Moure says
Need to find reliable contractor to resolve problem. I had new garage slab poured yesterday and woke up to 1/4 to 1/2 inch of water in the middle of garage floor and on the side corner of garage. Since i have not started building i hope it can be fixed. Any suggestions
Shea says
Hello Robert. You didn’t state where the water came from. Was it from an overnight rain or is it excess bleed water? We suggest starting with the contractor that poured your slab. They are the ones responsible either way. The criteria and specs for the slab should be outlined in your contract.
Robert La Moure says
Due to rain overnight. Trying to work it out . Thanks
Vince says
Thank you for this nicely written article. The first photo looks like my garage with the pooling water, except mine has an epoxy finished. Can I fill the low spots directly over the epoxy finish? What product would you recommend I use to fill the low spots over the epoxy finish?
Shea says
Hi Vince. You can apply an appropriate product over the epoxy to fill the low spot as long as the surface is prepped properly. Of course, it will ruin the look of your epoxy floor unless you plan on redoing it. For an epoxy surface, it will require that you rough up the epoxy with 60 grit sandpaper first. A 100% solids epoxy slurry would be the appropriate repair product.
Vince says
Thanks for the quick reply Shea.
I was hoping to patch cover the repaired spots. The floor is grey with black speckles.
Am I kidding myself that it will look ok when I’m done and should I just plan on redoing the entire floor?
Shea says
If you have a decorative finish on the surface, Vince, any repair or change like that is going to stick out like a sore thumb. 🙁 If you want it to look nice, it would require recoating the floor.
Vince says
I figured as much – appreciate your help with this!
Jas says
Have 4 inches of slope at the front of garage . I am converting carport to garage and slope is at front where the door comes from one side to other. What could be done ?
Shea says
Hi Jas. You can explain a bit more what you mean by the door coming from one side to the other? How is that in relation to the slope?
James says
I recently purchased an older place and the garage floor is a wreck. Someone pour a concrete repair over and uneven surface. I am trying to build my workshop and do not feel comfortable walking or standing in some spots it is so uneven. I noticed some spots are loose, so I plan to use my demo hammer to see what is underneath.
What will be the best way to get this to a sealed epoxy finish if I decide to tear it down to the blacktop?
Shea says
Hello James. Asphalt is oil-based and will not accept a coating. Epoxy, polyurea, etc. are for concrete and will not adhere. There are special paints for asphalt, such as what is used for road marking, but they are intended to be used as a working surface. From your description, you may need to rip out the current concrete/asphalt and place a new concrete slab.
Peter Holford says
I have low spot in one corner near garage door. In winter water puddles there because of snow outside. Tried seal under garage door but didn’t help. Guess I will be trying the epoxy slurry before winter. Try slight slope towards door. Be nice to have dry garage all winter. Size is appropriately 5’ x 2 1/2’ Will I find this at local building stores?
Shea says
Hi Peter. No, you will not find it at your local home improvement centers. Also, ask yourself where the water coming in under the door is going to go if you fill the low spot. If you are not going to be applying a coating to your concrete, then we would not recommend an epoxy sand slurry. It will look completely different and really stand out. Instead, we would recommend a polymer-modified cement product. It will look somewhat similar and not stand out as much. Here is an example of a good product you can order from Amazon. Based on your square footage, you will need a minimum of 2 pails. They list coverage rates based on the depth of the area and square footage.
Mitch says
Hi great article! Thank you it has given some good ideas
I have a garage that was finish with epoxy . A couple low spots in garage 3x 4 feet but not very deep less than a 1/4 inch deep. Seem like a crack runs across the garage that has made the low spots .
What would you recommend to level this out so water doesn’t puddle on those spots?
I live in bc Canada so it rains a lot and I get lots of puddles which annoys me
Shea says
Hello Mitch. Garage floors are rarely flat (we don’t mean level). It is costly for contractors to use the equipment and manpower required to achieve very flat concrete. It’s not an expense that most will justify for a garage. The occasional low spot of less than a 1/4″ here and there is not uncommon. Also, you can chase your tail around filling such low spots. The first question you need to ask yourself is where will the water go that you are displacing by filling the spot? Filling two or three low spots can move that water to collect in one larger area which was not a problem before.
If you still want to fill those areas, you need to keep in mind that it will ruin your epoxy finish and you will need to recoat the floor. For shallow areas like yours, a 100% sollids epoxy and sand slurry is best to use. The sand acts as a filler so that you don’t use as much epoxy. Here is an example from Amazon. Reduce the amount of sand required in the instructions by 25-30% in order to trowel it to a better feather finish. You may need to grind the current surface to remove the epoxy and expose the bare concrete.
mitchell cheng says
Hi Thanks for the quick response, I am not too worried about the finish of the epoxy as its a bit old and battered up. I have a couple of those large 3 x 4 feet areas where the water pools and just want it pushed towards the garage entrance.
Will the epoxy sand slurry be okay for larger areas and is it okay for edges of a garage as there is a gap between my garage and wall( I think an area of my garage where it pools sunk less than 1/4 inch ). Appreciate the info its been invaluable, I am trying to prep everything so I can do it right and get as much info as possible
Shea says
Hi Mitchel. If the depth is less than 1/4″, then the epoxy sand slurry is the recommended repair material to use. You will get a decent coverage rate at shallow depths and it will create a surface that is stronger than the concrete. Use an edging trowel at the expansion joint where the slab meets the wall. The sand in the epoxy will allow you to shape it properly.
mitchell cheng says
sorry just following up on this shea..what if the some areas depth is 1/2 inch? Been doing a lot of Reno but ready to tackle this garage
I was wondering if I should use concrete grinder the whole thing then use an exterior ardex self level the whole thing? or couple another option be to get it all epoxy and would the epoxy fill in the low spots? Wish you were in BC
Shea says
Hi Mitchell. When you go deeper than 1/4″ for larger areas, epoxy can get very expensive for the amount of material required. You would be better suited to use an Ardex product or similar (polymer-modified cement repair) to fill those areas. Make sure to read the data sheets thoroughly before you purchase anything. The data sheets will give you the exact information you need in regard to depth limitations and finishing.
mitchell cheng says
are the ardex repairs self levelling? how would I retain the slope needed to get the water out the garage?
Shea says
No, the type of Ardex required for the deeper repairs is not quite self-leveling. You can trowel the slope you need.
Shannon says
I’m hoping to repair my parents (84 & 81) concrete porch that has several low spots that hold water every time it rains. My greatest concern is for one of them to slip and get injured. So, I’m wondering if these same principles, used on a garage floor, would apply?
Shea says
Hi Shannon. Yes, it would be the same for a concrete porch.
Glen Cox says
Very informative. Thank you. I plan on applying a 100% solids epoxy over epoxy primer/sealer on garage floor. I have one area that is low in the front corner which I planned on filling, from 1/4″ feathered down, with Ardex CD.
However, I have noticed that the Ardex website states, “ARDEX CD should be sealed with a waterborne, breathable concrete sealer to prevent dusting and to help resist damage from standing water, salt and oil, as well as staining and marking.” Am I okay with the 100% solids epoxy?
Shea says
Hi Glen. Yes, you are fine. Ardex is just recommending that their product be treated with a sealer for best results. Just make sure that you allow enough time for it to cure and the moisture to evaporate out. It will need light grinding or heavy sanding once cured. You can’t etch polymer-modified cement.
Tom says
Are these self-leveling polymer cements different from self leveling underlayments? Which product do you recommend to level a small low spot priot to applying an epoxy coating? The self leveling underlayments seem to have the same marketing jargon as the cement, i.e. Henry 555 levelpro.
Shea says
Hello Tom. Yes, they are different. That is why we state in bold italics in the article above to not use self-leveling underlayments. They are not intended as a wear surface and they will not accept a coating properly. They don’t have the same compressive strength as well. If you just have one small low spot, we would recommend using a 100% solids epoxy instead. It will fill and feather small spots even better.
Cheng says
Hi,
Great site, I was wondering what you would recommend, I have a couple dips in my garage 1/2-1/4 inch ..a crack that runs across my garage with the side o the crack higher than the other side of the crack(seems like it has settle like this for long time now)
will the ardex k301 level everything out and prevent it from cracking down the road. or is there more issues like the base issue below the concrete slab?
Thanks
Shea Walker says
Hello Cheng. If the crack across the slab has not become larger in the past few years and the concrete has not moved, then it most likely will not settle anymore. The crack needs to be filled and repaired first. We recommend a product that uses a combination of sand and polyurea. A 1/2″ crack is large, so it will require much more product to fix. Here is an example of a product we recommend. After it has cured, you will want to grind the entire crack repaired area to make the transition more flush. After that is completed you can apply the Ardex K301 where necessary.