Why prep decides the result
Epoxy grips concrete mechanically. It needs a clean, dry, slightly rough surface it can soak into. Oil, old sealers, a smooth troweled finish and moisture coming up through the slab all stop it from bonding, and hot tires then lift the coating off in patches.
Step 1: Check the concrete's age and history
New concrete holds a lot of water. A common guideline is to wait at least 28 days after pouring before coating, but the epoxy maker's instructions take priority. Find out whether the floor was ever sealed or painted: sealers and old coatings must be removed, because epoxy will only be as strong as whatever it sticks to.
Step 2: Test for moisture
Tape an 18 × 18 in square of clear plastic sheet tightly to the floor on all four edges. Leave it for at least 16 hours, then lift it. If the underside is wet or the concrete has darkened, moisture is rising through the slab. Do this in a few spots. A wet result means you need a moisture-tolerant primer or professional testing before going further. This simple test is a screening check, not a measurement.
Step 3: Clean and degrease
- Move everything out and sweep thoroughly.
- Scrub oil and tire marks with a concrete degreaser and a stiff brush, then rinse. Repeat until water no longer beads on the stains.
- Scrape off paint drips, adhesive and anything else stuck to the surface.
Step 4: Open up the surface
| Method | How it works | Pros | Cons |
|---|---|---|---|
| Diamond grinding | A floor grinder abrades the top layer | Most reliable profile, removes thin sealers | Rental cost, heavy, creates silica dust |
| Shot blasting | Steel shot blasts the surface | Fast on large areas | Usually a contractor's tool |
| Acid etching | A diluted acid solution roughens the surface | Cheap, no machines | Less consistent, does not remove sealers, hazardous chemicals |
Many coating makers now prefer grinding. To see whether the surface is open, sprinkle water on it: it should darken and soak in within a minute or so. If it beads, the surface is still sealed or too smooth.
Step 5: Repair cracks and holes
Vacuum out cracks and fill them with an epoxy or polyurea crack filler, then grind the repair flush. Fill pits and spalls the same way. Leave control joints open or fill them with a flexible product as the coating system recommends, because the slab still moves there.
Step 6: Final clean and conditions
Vacuum the whole floor with a shop vacuum, then wipe or mop as the product directs and let it dry completely. Check the label's temperature limits; many epoxies need the air and the slab to be within a set range, often somewhere around 50 to 90°F, and the slab a few degrees above the dew point so condensation does not form.
Worked example: how much to buy
A one-car garage 22 ft deep and 12 ft wide is 264 sq ft. With two coats at 250 sq ft per gallon and 10 percent extra for the thirsty first coat, you need about 2.3 gallons of epoxy, three 1 gallon kits. Each coat goes on at about 6.4 mils wet. A deep 24 × 24 ft two-car garage, 576 sq ft, needs about 5.1 gallons, so six kits. A bigger floor also means more grinding, patching and cleaning, so allow extra prep time as well as extra kits. Use the coverage from your product's data sheet in the epoxy floor calculator, and run it separately for any primer or topcoat.
Plan the day
- Mix in small batches. Pot life after mixing can be short, especially in warm weather, and it gets shorter the more you mix at once.
- Cut in edges with a brush, then roll in sections, working away from the door so you finish at the exit.
- Respect recoat windows on the label. Too early and the coats mix; too late and the second coat may need sanding to bond.
- Wait the full cure time on the label before driving on the floor.
Safety
- Grinding concrete releases crystalline silica dust, which can cause serious lung disease. Use a grinder with a dust shroud and HEPA vacuum, and wear a properly fitted respirator.
- Etching acids burn skin and eyes and give off fumes. Wear chemical gloves, goggles and boots, ventilate, and add acid to water, never water to acid.
- Epoxy resins and hardeners can cause skin allergies. Wear gloves and long sleeves, and follow the safety data sheet.
- Turn off pilot lights and ignition sources when using solvent-based products.
Frequently asked questions
Do I need to grind or acid etch before epoxy?
Yes, one or the other. Epoxy needs a rough, open surface. Grinding is more reliable and removes thin sealers; etching is cheaper but less consistent.
How long after pouring concrete can I apply epoxy?
A common guideline is at least 28 days, but follow the coating maker's instructions and test for moisture first.
Will epoxy stick to sealed concrete?
Not reliably. Sealers and old coatings must be ground off. If water beads on the floor, it is still sealed.
Do the math for your own project.
Open the epoxy floor calculator