How to Prepare Your Garage Floor for Epoxy Coating

Here is a number that should stop you in your tracks: 80% of epoxy floor failures are caused by improper surface preparation. Not a bad product. Not a bad installer. Bad prep.

The epoxy itself is almost secondary. You could use the best 100% solids epoxy on the market, but if the concrete underneath is not properly profiled, cleaned, and tested, that coating is going to fail. Peeling, bubbling, delamination -- all of it traces back to what happened (or did not happen) before the first drop of epoxy hit the floor.

At AVS Painting, surface preparation is the step we spend the most time on. Here are the 5 steps we follow on every single project.

Step 1: Clear the Garage Completely

This sounds obvious, but it matters. Everything needs to come out -- cars, shelving, storage bins, tools, workbenches. Every square inch of the floor needs to be accessible.

Why? Because inconsistent prep creates inconsistent adhesion. If you grind 95% of the floor but skip the 5% under a toolbox, that 5% becomes the weak point where delamination starts and spreads.

We recommend clearing the garage at least the evening before installation day. If you need help moving heavy items, let us know during the estimate -- our crew can assist.

Step 2: Clean and Degrease

Concrete is porous. Over years of parking cars, oil, brake fluid, antifreeze, and road salt soak into the surface. These contaminants act as bond breakers -- epoxy will not stick to oily concrete.

What we do:

• TSP (trisodium phosphate) wash to cut through general grime and dirt
• Commercial degreaser on visible oil stains, applied and agitated with stiff brushes
• Pressure rinse to flush contaminants out of the concrete pores
• For severe oil saturation, we may use a poultice treatment that draws oil out of the concrete overnight

If you are doing this yourself, pay special attention to the areas where you park. The spots directly under where your engine sits and where you open your car door are typically the worst for oil contamination.

Step 3: Repair Cracks and Divots

Almost every garage floor has some cracking. Hairline cracks, spider cracks, and settling cracks are all normal in concrete. But they need to be addressed before coating.

What we do:

• Chase and fill cracks with a flexible polyurea or epoxy filler. We widen narrow cracks slightly (called "chasing") so the filler can bond on both sides, not just bridge over the top.
• Patch divots and spalling with a cementitious repair compound that is compatible with epoxy coatings.
• Respect expansion joints. Expansion joints (the deliberate grooves cut into your slab) are there for a reason -- they allow the concrete to expand and contract without cracking elsewhere. We honor these joints and can either fill them flush or leave them as control joints depending on your preference.

Important: Structural cracks (wide, shifting, or actively moving) need to be evaluated before coating. An epoxy floor will not fix a structural issue -- it will just hide it until the crack telegraphs through the coating. We will flag these during our inspection and recommend a course of action.

Step 4: Diamond Grinding

This is the single most important step in the entire process. Diamond grinding creates the concrete surface profile (CSP) that epoxy needs to mechanically bond to the floor.

Why Diamond Grinding Beats Acid Etching

Many DIY kits and budget contractors recommend acid etching (muriatic acid) as an alternative. Here is why we never use acid etching:

• Inconsistent results. Acid reacts differently with different areas of the same slab depending on the concrete mix, age, and contaminants. Some areas get a great profile, others barely get touched. Diamond grinding is mechanical -- it creates the same profile everywhere.
• Does not remove sealers or coatings. If your floor has ever been sealed (many new construction homes come sealed from the builder), acid will not etch through the sealer. The epoxy bonds to the sealer, the sealer fails, and your new floor peels off. Grinding physically removes old coatings and sealers.
• Hazardous waste. Muriatic acid creates toxic fumes and hazardous wastewater that needs to be neutralized and properly disposed of. In a residential garage with no drain, this is a real problem.
• Leaves residue. Acid etching leaves a calcium chloride residue on the surface that must be thoroughly rinsed and neutralized. Any residue left behind compromises adhesion.

Our diamond grinding process uses industrial-grade planetary grinders with diamond-segment tooling. The grinder removes the top layer of the concrete (called laitance), opens the pores, and creates a CSP 2-3 profile -- the ideal texture for epoxy adhesion. The dust is captured by our HEPA vacuum system, so your garage stays clean.

Step 5: Moisture Testing

Moisture is epoxy's silent killer. Water vapor migrating up through the concrete slab will push the coating off from underneath. This is especially common in New England, where basements and garages sit on high water tables and deal with seasonal moisture fluctuations.

What we do:

• Calcium chloride test (ASTM F1869): We place sealed calcium chloride test kits on the freshly ground concrete. After 60-72 hours, we weigh the moisture absorbed. If the moisture vapor emission rate (MVER) exceeds 3 lbs per 1,000 sq ft per 24 hours, we know there is a moisture issue.
• Plastic sheet test (quick visual): As a preliminary check, we tape a 2x2 ft piece of plastic to the floor. If moisture droplets form underneath within 24 hours, the floor has a moisture problem.

If moisture is present, we are not going to tell you everything is fine and install anyway. We will recommend a moisture mitigation system -- a specialized primer that creates a vapor barrier before the epoxy goes down. This adds cost, but it is the difference between a floor that lasts and a floor that blisters and peels within a year.

DIY Prep vs Professional Prep

Can you do surface prep yourself? Technically, yes. But there are some honest considerations:

• Equipment cost. Renting a concrete grinder runs $200-400/day. HEPA vacuums, diamond tooling, and moisture test kits add up. For a one-time project, you will spend $300-600 on equipment rental alone.
• Learning curve. A concrete grinder is not intuitive. Go too fast and you skip areas. Go too slow and you gouge. Miss an edge and the epoxy peels there first. Our crew grinds floors every day -- that experience matters.
• Time investment. What takes our 2-person crew 3-4 hours will take most homeowners an entire weekend, including cleanup and re-cleaning.
• No do-overs. If you grind poorly and apply epoxy over it, stripping the failed coating and re-grinding will cost more than professional prep would have cost from the start.

If you are the kind of person who takes pride in doing things right and wants to invest the time, DIY prep is doable. But for most homeowners, the professional prep is where the real value of hiring a pro lives. The epoxy application itself is actually the easy part -- the prep is where the skill is.

The Bottom Line

Great prep is invisible. When your epoxy floor looks flawless five years later, nobody thinks about the hours spent grinding, filling, and testing. But when a floor fails, the prep (or lack of it) is almost always the cause.

At AVS Painting, prep is not a step we rush through to get to the "fun part." It is the foundation that everything else depends on. It is why our floors last, and it is why we confidently offer our 10-year guarantee.