How to Level and Fix Low Spots on Your Garage Floor

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.

This post may contain affiliate links. If you use these links to make a purchase, we may earn a small commission. As an Amazon Associate, All Garage Floors earns from qualifying purchases. You can read our full disclaimer here.

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.