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Surface Preparation for an Epoxy Garage Floor

Updated on August 2, 2014

Read this BEFORE you install an epoxy floor

Here are critical surface preparation and installation steps you need to accomplish to ensure an attractive and durable floor.

Don't skip these steps or you will be VERY unhappy later when the floor coating fails. Better to be safe than sorry.

Why is surface preparation so important?

Doing it right the first time

The concrete surface must be clean, porous and not have a sealer, oil, paint, wax or mastic on it or the epoxy won't have a chance to sink into the pores and thoroughly bond to the concrete.

Intrusion by water from under the slab will also cause big problems and must be addressed. The most obvious symptoms of water intrusion are continually damp areas, areas which generate a white powdery substance (efflorescence) or areas where the concrete surface is crumbling or flaking off. If any of these conditions are present you must test your concrete for MVE (moisture vapor emissions) before applying any coating. (See "Testing your concrete floor" below.)

Cracks and holes in the floor must also be treated. The epoxy might cover over tiny hairline cracks but anything more than a hairline will allow the epoxy to wick down and leave an unsightly crack or hole.

Quality epoxy is a two part system. One part is a resin and the second part is a hardener. When the two materials are mixed they chemically react and create a final material which has a high abrasion resistance, has excellent bonding characteristics and has high moisture intrusion resistance. It still needs good surface preparation but it will be FAR thicker and more durable than the water-based epoxy in the $99 hardware store kits.

Testing your concrete floor for porosity

This isn't rocket science - but it is important

This is very simple. Just spill a few tablespoons of plain water on various parts of the floor. If the wet area turns dark quickly it is porous and you are good to go. If the water instead beads up and does not penetrate quickly, you've got a porosity problem. Non-porous concrete won't allow the epoxy to penetrate and grab into the slab. Any coating on a non-porous floor WILL peel . . . probably sooner than later.

You can get a benchmark by dropping a few tablespoons of water on various areas of your concrete driveway or sidewalk. They are probably not sealed and the water will darken the concrete almost immediately. That effect is what you are looking for in your garage floor prior to epoxy coating it.

Suspect areas of a floor are ones that have dark stains from oil and automotive fluids, have white powdery areas and/or areas that have a shine (porous concrete is not shiny).

Floors that have previously been painted or have carpet adhesive or tile mastic on them are an immediate problem. DON'T try to coat a floor if these materials are present. Any coating won't adhere properly.

If the concrete floor looks clean, do the water test anyway. It only takes a couple of minutes. Sometimes concrete contractors put down a curing agent on the new concrete to keep it from drying out too quickly. That curing agent usually leaves a sealer on the concrete which prevents the epoxy from bonding properly.

Floors with a shine, paint or carpet adhesive

How to take the gunk off

Carpet glue and tile mastic are probably the easiest to deal with. The safest product to use is BEAN-e-doo from Franmar Chemicals. It is a soy-based product that emulsifies the old mastic. When it has done its job, just scoop up the residue and mop off the floor with water. You can buy BEAN-e-doo directly from Franmar or contact them for a local dealer. Click here for Franmar's web page. You can also get BEAN-e-doo from our epoxy materials supplier, Versatile Building Products Click here for Versatile's web page.

Another possibility is to get an adhesive stripper from a local carpet supplies distributor. (Check your local yellow pages for carpet supplies distributors). They will usually have one formula for the yellow/tan adhesive and another for the black adhesive. They are usually environmentally friendly and are applied the same as the BEAN-e-doo. Follow the instructions on the container. It is going to be gooey and messy but this adhesive must come off.

Painted floors or floors that do not pass the water test (above) will need to be stripped and/or ground down with a diamond cup grinder and attached vacuum. For grinding, you might be able to rent an angle grinder with a 7" diamond cup wheel, dust hood and vacuum but it is difficult to work with and it is all too easy to scar the floor with the grinder. It is highly recommended that you hire a professional to grind the floor.

Acid etching WILL NOT work on these problem areas. Solvent based chemical strippers containing Methylene Chloride will work on the carpet adhesive, paint and oil but will be messy and noxious. Methylene Chloride is effective but WILL burn you skin. (If you decide to use one of these strippers, keep a 5 gallon bucket of water or hose nearby to quickly wash off the splatters. You will quickly know what I mean if you use them.)

Removing oil and auto fluid stains

There are many degreaser products on the market which can be obtained from hardware stores, janitorial supply stores and some paint stores.

Some have noxious chemicals and some are environmentally friendly. Read the labels. Perhaps the friendliest is a degreaser that contains orange oil and a powdery material in solution. The orange oil emulsifies the old oil and the powdery material soaks up the oil to the surface. It takes about 24 hours to work but is much less messy and is not at all noxious. When the powder is dry, simply sweep it off and retest the treated area for porosity with a little water. You might have to do this application more than once to remove the oil and open up the concrete pores for the epoxy. The goal of this cleaning is not to make the concrete look clean and gray but to make sure that it is porous so the epoxy can grab on.

We use Versatile Building Products' V-100 cleaner. You can find it at Use the 'Search' box at that site to look for 'V-100'. It is amazingly effective, quick and is not noxious.

Epoxy/urethane paint removal gels work well on oily surfaces but they contain Methylene Chloride. This is nasty stuff and WILL burn your skin. It will also remove your epoxy floor coating. Definitively not recommended.

In extreme cases where you have a thick layer of dirt-caked oil, first try to scrape off the layers down to the concrete with a stiff scraper. If that doesn't work you may have to burn the caked-on oil with a propane torch and then scrape. (Don't use too much heat or the cold concrete surface might pop off . . . which causes another repair problem.) Then proceed with a degreaser as described above.

Diamond Grinding

The ultimate solution

If your floor is non-porous, professional installers will normally use a 7" angle grinder or a walk-behind grinder with a diamond grinding wheel and an attached heavy duty vacuum to scuff up the concrete surface and provide porosity for the epoxy to sink into. This is called "profiling" the floor. The result will be a surface that feels like 100 grit sandpaper.

A homeowner MIGHT be able to rent such equipment from a rental yard but it is not advisable. It is all too easy to gouge your garage floor by leaving swirl marks in the surface or hurt yourself or the equipment if you are not experienced in its use. If you decide to go ahead anyway, DON'T EVEN THINK about renting a grinder without a dust hood and an attached heavy duty vacuum. Otherwise the grinder will create clouds of messy and lung-damaging concrete dust. Even with the dust hood and vacuum some concrete dust will escape. You should tape up the seams of cabinet doors and entry doors with 1 1/2" blue painter's masking tape to keep the dust from coming in.

Acid washing

Another way to go . . . but not recommend

Assuming that the concrete has been thoroughly cleaned of oil, paint, etc., acid washing is an alternative to grinding a concrete surface. The goal of both techniques is to produce a porous surface for the epoxy to dive into.

Acid washing does have its own set of problems though. After acid washing and before the surface dries, you will need to pressure wash off the whole surface to get rid of the concrete sludge that the acid will bring up. (Otherwise it will just clog the newly opened pores again.)

You should be able to rent a gasoline powered pressure washer (2500 - 3500 PSI with 4+ gallons/minute water output) from your local hardware store for about $50/day. Also rent a 'turbo tip' for the pressure washer. This type of tip produces a cone of spray and is much less likely to scar your concrete than the standard tips that come with most pressure washers. (Don't even bother with the small electric models that are made for much lighter weight jobs like cleaning your car or tires. They just don't have the power to get the job done on concrete.)

Most professional installers of epoxy floors do not acid wash or pressure wash. There are just too many opportunities for the high pressure spray to damage the sheet rock, other wall covering or cabinets to risk it. It also requires a huge amount of water to accomplish the task. The appropriately-sized pressure washer puts out 4-5 gallons of water per minute. (Your local environmental protection agency also might take a dim view of flushing an acid solution down the storm drain.)


If you decide to acid wash, use Muriatic Acid (pool acid) from your local hardware store or pool supply store. Mix it at 1 part acid to 10 parts water. ALWAYS add acid to water, not the other way or the acid might splash. Wet the concrete surface lightly with water and, using rubber gloves and boots, pour the acid solution over small (10 ft sq or so) portions of the floor and scrub it with a stiff acid brush on a pole. The solution should foam if the acid is working properly. Do not allow any acid-treated areas to dry. Pressure wash them off quickly and thoroughly. It is also a good idea to neutralize the acid by drenching the acid treated surface with a solution of 1 part of household liquid ammonia to 10 parts of water (a pump-up sprayer works great for this) and pressure washing it down again with plain water.

Note: The acid solution will eat holes in your clothes and shoes if it splashes on you. As soon as you are done acid washing, neutralizing and pressure washing, throw your clothes in the washer. The alkaline soap will neutralize any remaining acid. Wash your skin and shoes (if not machine-washable) off with hot soapy water.

The acid washing will produce a fine slurry of wet concrete dust. The pressure washing is necessary to remove that slurry so that it won't just plug up the porous surface just created. Be aware that the slurry going down your driveway from the garage will make a mess and could etch the driveway surface if you don't neutralize it. (You can neutralize the acid with a 1:10 dilution of liquid ammonia and water applied with a pump-up sprayer or watering can.) You will also need to pressure wash the driveway. (Check with your local EPA about flushing this slurry and any acid residue down a gutter into a storm drain.)

Obviously the garage concrete surface will be wet after such a treatment. You will need to let it dry naturally for a few days. The process can be accelerated by using a big fan or a leaf blower. Only the highest quality 2 part resin based epoxies will bond properly to a damp concrete surface. If you are using a lesser quality epoxy, let the concrete surface dry out for a day or two longer than when it looks dry.

Cracks, holes, lifting and spalling

Dealing with concrete flaws

Cracks: Cracks fall into two categories: those 1/8" wide or less and those wider. Small cracks can be filled with an acrylic-modified concrete patching compound. Make sure to get one with no sand.

Cracks over 1/8" wide must be ground out with a diamond grinding wheel called a crack-chaser. This will open up the crack to about 1/4" wide and 3/8" deep. Then a two part urethane patching compound should be poured into the crack and topped up with sand (it adds strength and a rough surface for the epoxy top coat to grab onto). When the urethane patch is cured it needs to be ground down with a diamond grinding wheel to provide an even surface. This is best done by professionals who have the appropriate tools and experience.

Holes and chips: Holes in concrete are usually caused by a rock in the concrete mix being too close to the surface. In subsequent years expansion and contraction of the concrete causes the rock to break through the surface and fall out.

Chips in the floor usually occur when something very heavy is dropped on the floor causing the concrete surface to fracture. They can also occur at the edge of the slab next to the driveway if an expansion joint wasn't installed when the slab was poured. Chips are normally shallow along the edges leading to a deeper indentation near the center.

Both types of holes can be successfully repaired with an acrylic-modified cement patching material. However, a shallow chipped area must first be ground out to a depth of about 3/8" with vertical walls to allow the patching material to attain maximum strength. Follow the instructions on the container of the patching material. It will undoubtedly direct you to dampen (not drench) the area to be patched with water prior to applying the patch. This is called SSD or Surface Saturated Dry. Moistening the existing concrete will prevent the dry concrete from sucking out the water from the patching material and will increase the strength and adhesion of the patch.

Lifting: Lifting creates a ledge along a crack line or next to an adjacent slab. This produces a trip-and-fall hazard. Lifting is usually caused by earth settling or tree roots. Have a professional check out the source of the problem to see if it can be fixed first.

The trip-and-fall hazard can be reduced by grinding down the edge, tapering it back towards a level area and filling any cracks. (Resist the temptation to grind off more than about 1/3 of the thickness of the slab as it will weaken the slab too much.) Your floor won't be perfectly flat but the safety hazard will be substantially reduced. Again, because of the hazards involved, we highly recommend that you have a professional do the grinding.


Spalling is the condition where the concrete surface is heavily pitted and may be actively crumbling. It is usually caused by water coming up through the slab and along crack lines. This water intrusion causes the surface of the concrete to pop off along the crack. It might also be caused along the front edge of the slab by rainwater falling off the eaves and eroding the surface.

In these cases we use a 1/4" crack chasing diamond grinding wheel to grind off the loose material and cut down the surface to about 3/8" deep with vertical walls. Patching materials are MUCH stronger and effective when applied to deep areas rather than to shallow areas.

We use Versatile Building Products' 4150 epoxy (a highly water-resistant epoxy) mixed with their acrylic-modified mortar mix. It creates an extremely strong patch.

Will the concrete ever crack again?

Never say 'never'

Any crack repair system or epoxy coating is not a Star Wars force field which will protect your floor from all perils forever. Concrete cracks because the base under the concrete was not properly compacted, the contractor did not insall steel rebar or mesh, the contractor did not put in tension-relief cuts every 10 feet AND/OR because of earthquakes, soil settling and tree root invasion.

If tens of tons of concrete flooring want to move for whatever reason, nothing will stop it. Don't expect an epoxy floor contractor to guarantee that cracks will never appear again. If he does, BE CAREFUL - it is just not possible.

Future cracks can be minimized, not totally cured, if a qualified contractor cuts around the crack with a diamond saw and installs rebar in the patching material across the crack. This process is expensive and not a permanent solution.

If a quality epoxy coating product with a 100% broadcast of decorative chips has been applied, future crack repairs can be easily accomplished without the appearance of a patch.

Water intrusion

A BIG potential problem

Areas of the floor that are usually damp or produce a white powdery substance (calcium chloride and other minerals) have a water intrusion problem that will cause problems with adhesion of your epoxy floor. Acid washing the floor with common household white vinegar will temporarily get rid of the white powder but is NOT a permanent solution.

The manufacturer of your epoxy coating will be able to give you a maximum MVE (moisture vapor emission) resistance number for their product. If you suspect a moisture problem, have a professional test it or Click here for Taylor Tools' web page. Taylor has test kits which will determine the MVE and alkali content of your slab. Two test kits are needed for a 2-3 car garage area at about $18 each. The test must be terminated promptly within a 48-60 hour window and the testing materials mailed back to Taylor in their self addressed shipping envelop for a free report of the results.

A quick and cheap initial testing method is to cut an 18" - 24" square of plastic (a trash bag will do) and tape it down to the garage floor with duct tape. Take it up after 24 hours. If the floor is darkened or damp or if there is condensation on the bottom of the plastic, you have a moisture problem. If the results indicate a moisture problem, you or a professional should continue testing and use the Taylor test kits for specific results. The epoxy manufacturer will be able to tell you whether or not their epoxy can withstand the MVE numbers Taylor gives you. If not, remedial measures to stem the water intrusion are necessary.

A professional should be consulted to determine the cause of the water problem. It could be a leaky water pipe under or near the concrete, improper grading of the soil around the slab so that irrigation water and rain flows towards the slab rather than away from it or any number of other problems. It is highly preferable to fix the source of the problem before continuing with a coating.

There are products which when applied to the concrete will create a moisture barrier against water intrusion . . . but only up to a point. It is far better to fix the cause of the problem first.

Surface moisture test kit - Testing is essential if you have evidence of moisture on your garage floor

Evidence of a moisture problem includes patches of white powdery material, darkened damp areas; little volcanoes of gray, rust, tan or black dusty material, crumbling stem walls and/or a musty smell in the garage.

The goal of cleaning

Why go through all this trouble?

The goal of degreasing or otherwise cleaning your floor for an epoxy coating is not to give you clean looking concrete. Some dark spots from the oil and auto fluid stains or rust may remain after the treatment. The goal is to create a porous surface for the epoxy to grab into and so that it can last and cover any remaining stains. As mentioned before, the cleaned surface can be tested again for porosity by splashing a little water on it to see how quickly it turns dark. You may have to repeat the cleaning process to gain the porosity needed for the epoxy to adhere properly.

About Us

California Concrete Restoration, Inc. has specialized in installing epoxy garage floor systems and cement overlay systems on driveways, walkways and patios in the Southern California area since 2004.

The information we have given you here is probably overwhelming. To do the job right and give you a 10+ year warranty, professionals go through these steps religiously. Concrete is a much more complex product than most homeowners imagine.

Contact us for a free evaluation and quote on your concrete floor in the Southern California Orange County area or for a reference to a professional in your area. If you are outside the Orange County area, please email us your name, location, phone, email information and a description of your project so that we can put you into contact with a professional installer in your area.

Note: Our firm is retained by Versatile Building Products, manufacturer of the materials we use, as Moderator of their dealer forum web site.

California Concrete Restoration, Inc.

Laguna Hills, CA

(949) 939-4088

Click here to email us:

Click here to see our main web site.

Check out our free report below

Read our Free Report: "The Truth about Epoxy Garage Floors"

This is a discussion of the various available epoxy garage coating systems. It will give you valuable information about the cost, durability and appearance of these systems. Read it FIRST before selecting an epoxy coating system for your floor.

Reader Feedback - Tell us if this information was valuable to you

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    • calconcrete profile imageAUTHOR


      5 years ago

      @johnmark123: Glad it helped you.

      As you know, proper surface preparation for ANY coating is about 60% of the job. Whatever the quality of materials you put down, they won't look good and will fail sooner than later if the surface isn't properly prepared.

      Many homeowners do not understand this concept unless it is explained to them. Some think that we can just come in and slop down some $20/gallon coating over what is there and that it will look good and last for decades. That is false economy on their part.

      I only take jobs where the homeowner understands the costs of a proper surface prep and only use high quality materials. I don't want to have to come back on the job later.

    • profile image


      5 years ago

      Good info. This lens helped me so much.

      Backflow Installation

    • profile image


      5 years ago

      @opatoday: Glad you liked it. We keeping adding to the lens but there is not much more to say.


    • opatoday profile image


      6 years ago

      Great info keep up the good work

    • profile image


      7 years ago

      I really enjoyed reading your lens. You did a fantastic job!

      One squid thumbs up vote issued for this lens :)

    • calconcrete profile imageAUTHOR


      8 years ago

      @GarageGuy: Dave,

      Sounds like we are in the same business.

      I look for dark water marked spaces on the concrete floor (not just oil spots) and look for efflorescence.

      Some concrete floors are not a good candidate for an epoxy coating unless the homeowner is willing to pay for a fix of the water-intrusion problem. Applying epoxy and sealer is not a Star Wars force field for the floor.


    • profile image


      8 years ago

      Very informative, nice post! Water intrusion is very often an issue that sneaks up on people. Many times you don't know it's a problem until repairs are required. Nice work!


      [url=]Flooring for Garage[/url]

    • profile image


      8 years ago

      I really liked the lens. It's fabulous. Garage doors has got a great variety and it is one of the great examples!

    • profile image


      8 years ago

      Great Information!

    • calconcrete profile imageAUTHOR


      9 years ago

      @Petar: Petar,

      Thanks for the feedback. It's always good to know that we are providing valuable information.

    • profile image


      9 years ago

      Great lens. Loads of good info and suggestions.


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