Learning the best way to clean a garage floor properly is a skill that is high on most home improvement lists. It is a critical aspect for any project that involves prepping a floor for paint, an epoxy coating, or for just creating a nice clean garage floor free of spills, stains, and contaminants.
Depending upon what type of garage floor project you have chosen and how dirty your floor is, there are different methods of cleaning a concrete floor that you may want to engage. We will discuss each of them as we go in order to assure a successful outcome. If your goal is to eliminate pet urine odor and stains, then we have a separate article for that here.
Scrubbing the garage floor clean
For the best success, the first thing you want to do is remove everything from the garage floor that is not anchored down and sweep out the heavy dirt and debris. As obvious as this seems, there are people who don’t want to do this and they are the ones who always end up ruining something due to water damage.
If you have painted drywall in your garage or low electrical outlets, you may want to cover the lower 3ft. by taping a few cheap plastic drop cloths to the walls to avoid water spots or shorts from electrical damage.
The easiest low budget method for cleaning the garage floor is to use a concentrated concrete degreaser
Mix the cleaning agent of choice into a large bucket of warm to hot water. For Tide we like to use a ratio of 1/3 cup of Tide to 1 gallon of water. Follow the recommended directions for the TSP or degreaser. It is easiest if you divide your floor into sections as you clean.
Pour your warm soapy solution onto a section and start scrubbing with your deck brush. For particularly dirty floors it helps to let the solution set for a few minutes after your initial scrubbing in order for it to work on the dirt and grime. After it has set for 5 – 10 minutes, add a little more solution and scrub again. Follow that up with a good rinsing with your high pressure nozzle and then move on to the next section.
What’s important here is to make sure that the solution you are scrubbing with does not start to dry up before you rinse it away. The reason for this is that the contaminants in the pores of the concrete are emulsified and lifted out in the solution while it is still wet. This makes it easy to rinse out with the high pressure nozzle. If it starts to dry out, these contaminants can be left behind with the rinsing.
Once the floor dries you should have a nice clean surface and can inspect for any tough areas that need to be spot cleaned such as grease and oil stains.
Equipment for cleaning a garage floor
Concrete is porous and can really become embedded with dirt and grime over the years if it hasn’t been cleaned very often or at all. If you are dealing with a floor such as this then you do have some equipment options that can make the job easier and work great at getting the dirtiest of garage floors clean.
The first of these is a pressure washer. Pressure washers can save a lot of time in scrubbing and are excellent at cleaning concrete. Most will allow you to add a degreaser to the water for additional cleaning action. You can read more about pressure washers for garage floors here.
They are not very expensive to rent and you can usually find them at your local home improvement or equipment rental centers. For effective cleaning, a minimum 3000 PSI washer should be used with a water flow rate of 3 gallons per minute or more.
The key to using a pressure washer is to presoak the concrete with the cleaning solution first for 10 – 15 minutes. Work in sections as stated above. Once the area has soaked, add more water to the floor and use the pressure washer to start rinsing the grime away.
The yellow 15 degree fan tips work best for dirty concrete. For particularly stubborn areas such as stains, you can use the more powerful turbo tip. Just be careful not to linger too long in one area when using a good pressure washer and keep the tip moving. Because the water action is so abrasive, you can actually etch the surface of the concrete if you are not careful.
The second equipment option you can use is a floor buffer (also known as floor maintainers) with a nylon scrubbing head for concrete. You can rent these inexpensively as well. Be sure to tell the rental company that you will need a head for cleaning concrete. Home Depot is a great resource for these.
When using a floor buffer you will clean the concrete in the same manner as if using a deck brush. Just substitute the floor buffer for the deck brush. Take your time as you go and let the buffing machine do its work. You may have to add a little water as you scrub to keep the solution wet and foamy.
These can do wonders to some concrete with the floors turning many shades lighter after scrubbing with a floor buffer.
Cleaning oil stains and grease
With the heavy cleaning done, you can now tackle the oil and grease stains that were not completely removed by the scrubbing.
Wet the stain and surrounding area first then apply your degreaser to the oil spot in full strength. The reason for wetting first is to prevent the contaminants in the stain from spreading to a dry area. Scrub the degreaser in and let it sit for a while. Apply more degreaser, scrub, and then rinse with the high pressure nozzle.
Mixing a heavy concentration of Tide into something closely resembling a liquid paste works well also. Just make sure the concrete is wet before you apply it and scrub it in. Again, let it sit without drying out before you rinse it. These methods will take care of most standard oil and grease spots.
If these methods don’t remove all the oil stain, there are advanced methods for removing oil stains below.
How to remove oil and grease stains from concrete
Be advised that older stains that have been in the concrete for a long time will still have some discoloration. To make sure that you were successful in removing the oil, test it by sprinkling a few drops of water onto the surface. It should not bead up. If the water doesn’t soak in or beads up on the surface, then that is an indication that it was not all removed and you may have to clean it again.
Removing rust stains in concrete
There are a few ways in which to rid your garage floor of rust stains. For small spots, the simplest is to use either lemons or white vinegar. The white vinegar is easier to use if the spots are larger. Squeeze the lemons or pour the white vinegar over the stain and let it sit for 5 minutes or more. Add some more lemon juice or vinegar and then scrub with a good stiff brush. Rinse well with water and repeat if necessary.
A high concentration of TSP mixed with boiling water works wonders on rust as well. Be sure to let it sit on the stain for about 15 to 20 minutes before scrubbing. Repeat if necessary.
Oxalic acid is another product that is even tougher on rust stains. You can generally purchase it from your local home improvement center or hardware store. Some concrete cleaners for rust stains have it as an ingredient. It may even come in a powder form which you mix with water to make a soupy paste.
Apply the Oxalic acid to the stain and let it sit for 5 minutes before scrubbing. Be sure to rinse real well afterwards. Again, repeat if necessary.
Another option is to use one of the concrete rust stain remover products that are available over the counter. You can see a whole list of some of these products here from Amazon
For the toughest of rust stains a mild solution of muriatic acid will work wonders, but you need to be careful when using it. We suggest a ratio of 10 parts water to 1 part acid to start. More isn’t always better in this regard unless you are preparing your concrete for a floor coating. If you mix it too strong right away it will etch the concrete which will make it look different from the surrounding concrete.
For more instructions on how to use acid on concrete we suggest you read this post here.
Removing old paint and sealers
If you are applying a coating to your floor, you will need to remove any type of residue on the surface such as a thin filmed topical sealer, old paint, or mastic. This needs to be done first before any attempt is made at cleaning. There are two different methods you can use depending upon what is on the concrete.
The first would be a chemical stripper. We highly recommend a couple of products that are available from Franmar Chemical that are environmentally friendly and very effective. The first product is called Bean-e-doo and works great for removing mastic. The second is Soy Gel and is very effective for the removal of old paint and urethanes.
These type of products are more expensive than solvents and take a little more time to work on the product (chemically, not physically), but are much more safe for you and the environment. If you are cleaning the garage floor before laying down a floor covering such as roll out mats or interlocking tiles, then removal of old sealers are not necessary.
The other method is to use a floor grinder. Special grinding heads are available for the purpose of removing mastic, paint, and sealers. While it can be a more dusty way of dealing with old sealers and paint, it does require less elbow grease than chemical strippers. It does cost more however. You can read more about using floor grinders for concrete here.
Final Cleaning Tips
One tool that can come in handy is a floor squeegee. These work great at moving large volumes of water out of the garage and for clearing water out of low spots. If you don’t have a squeegee an old push broom will help. You can find great prices on floor squeegees here from Amazon
One important note to make; if you are planning on acid etching your concrete in preparation for paint or an epoxy coating, then you still must clean your garage floor as stated above. Acid works by breaking down the surface of the concrete to expose the pores. It will not clean away dirt or remove oil.
If you plan on grinding your garage floor then you only need to treat the oil stains. Any other surface contaminants such as dirt and most rust stains will clean up with the grinding.
If followed correctly, you will find that these methods of cleaning a garage floor are highly effective. It is generally thought of as the least desirable part of any floor project or garage cleaning chore, but once done it will reward you with a nice clean concrete floor that is free of dirt and stains.
Is it safe to use acetone to clean a concrete garage floor that has been saturated with car chemicals for the last 30 years with no attempt to ever clean a spill?
Hello Tony. Acetone helps to emulsify oils in order to lift them from a surface. It needs to be used in conjunction with a poultice in order to absorb oils. This article on cleaning oil stains explains how the process works. Acetone does not clean concrete like a degreaser. Always make sure there are no open flames when using large quantities of acetone before covering with a poultice. We always recommend degreasing the concrete first by scrubbing or pressure washing methods first before using acetone for cleaning stubborn areas.