Epoxy Over Painted Concrete
The short answer
You can, but you are betting the entire floor on how well somebody else's paint is stuck down. Epoxy bonds to what it touches. If the paint lets go of the concrete, your coating leaves with it, and the bond line that failed is not the one you applied. Test the paint before you decide, and understand that on most jobs the cheapest honest route is to grind it off.
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The substrate
Find out what is actually on the floor
"Painted concrete" covers several very different materials, and they do not behave the same way.
- Latex or acrylic garage floor paint. Thin, flexible, usually poorly bonded because it went down on a slab that was never profiled. The most common thing under a failed recoat.
- Solvent alkyd or oil based floor enamel. Harder and often better bonded, but it chalks and it can soften under solvent.
- Chlorinated rubber or old deck paint. Found on older industrial and pool deck slabs. Softens readily and is a poor base for anything.
- A previous "epoxy paint" kit. Frequently a water based product with a small epoxy component, not a 100% solids system. It is much weaker than what you are about to put on top of it. If it is a genuine cured epoxy, read epoxy over old epoxy instead.
- A curing compound mistaken for paint. A sprayed membrane from the original pour, not a coating at all. Covered on epoxy over new concrete.
Settle it in an hour
Two tests that tell you what you need to know
The tape pull test
Pick several spots across the floor, including the worst looking ones and at least one in a traffic lane. Score an X through the paint down to the concrete with a utility knife. Press a strip of strong tape firmly over the X, leave it a minute, then rip it off fast and flat. Paint coming away with the tape means that paint is not holding the concrete, and anything you put on top of it holds no better. One failed spot condemns that area. Several failed spots condemn the floor.
The water drop test
Put a few drops of water on the paint in several places. If the drops sit and bead for several minutes, the surface is sealed and nothing is going to soak in or bond mechanically. If they darken and absorb, the surface is at least open. A sealed floor is not automatically a stop, but it does mean the profile has to come from abrasion rather than absorption.
Do both tests before you order material, not after. They cost an hour and a roll of tape.
The failure mode
The weakest layer decides the floor
This is the part worth being blunt about. A 100% solids epoxy build coat is dramatically stronger than old floor paint. When the floor fails, it does not fail at your coating. It fails inside the paint film, or between the paint and the concrete, and your expensive new system comes up as a sheet with the old paint stuck to the back of it.
That means every strength number on the data sheet is irrelevant on a painted floor. The floor performs to the weakest layer in the stack, and on a painted slab the weakest layer is the one somebody rolled on years ago without grinding first. You cannot improve it from above.
The second failure is lifting. Solvent in a topcoat can re-soften an old alkyd or rubber paint, and the softened film wrinkles and releases under the new coating while it cures. If you do not know the chemistry of the paint, you cannot predict this.
The work
The prep sequence, and the recommendation
The recommendation first: grind the paint off. On most floors, removing paint costs less than removing a failed coating plus the paint plus doing the job again. If you are coating a floor you intend to keep, full mechanical removal down to clean open concrete is the route that does not come back.
- Degrease before you grind. Grinding contamination into the profile makes it worse. Clean the oil off first, especially in traffic lanes and under vehicles.
- Grind to clean concrete. Diamond tooling on a planetary grinder, working to an open profile around ICRI CSP-2. Paint loads up tooling fast, so plan on more segments than a bare slab would need.
- Do the edges and corners properly. This is where a partial removal fails. A hand grinder with cup wheels gets the perimeter that the walk behind cannot reach.
- Repair what the paint was hiding. Paint covers spalls, cracks and old patches. Fill them once the concrete is exposed.
- Run a moisture check. The paint has been acting as a partial vapor retarder. Once it is off, test the slab before you seal it again.
- Vacuum, prime, coat.
If the tape test passed everywhere and removal genuinely is not on the table, the minimum is uniform abrasion over 100 percent of the painted surface so nothing glossy is left, a full degrease, and a primer. Go in understanding that the old paint is now the limiting layer, and that the floor's life is its life.
What to order
The material each step takes
| Step | What it does | What we stock |
|---|---|---|
| Degrease | Removes oil so grinding does not drive it into the profile | Accessories, safety and PPE |
| Remove the paint | Takes the weakest layer out of the stack entirely | Floor grinders, large and industrial grinders |
| Tooling | Paint loads segments fast, so tooling is a consumable here | Turbo Supreme diamond cup wheel, cup wheels and diamond tooling |
| Control the dust | Paint dust and silica both need to be captured at the head | Dust collectors and vacuums, dust extractors |
| Repair what was hidden | Fills the spalls and cracks the paint was covering | Everflow EF-135 crack filler |
| Barrier, if the slab reads damp | The paint was a partial vapor retarder; once it is gone, check | Premera Easy MVB, moisture vapor barriers |
| Prime | Keys the build coat to freshly opened concrete | Primers |
| Build coat and wear course | The structural layer and the abrasion layer over it | Epoxy floor coatings, polyaspartic topcoats |
Sizing the job
Budget the tooling, not just the resin
On a paint removal job the diamond tooling is a real line item and it is the one most estimates miss. Freshly ground concrete is also thirstier than a sealed painted floor, so the first coat goes further on paper than on the slab. Measure the footage and run it through the coverage guide. If you are choosing a machine rather than renting one, the grinder buying guide covers sizing.
Before you order
Related guides and the rest of the catalog
Talk to a supplier
Send us the floor, not just the square footage
Tell us what is on the slab now, what the moisture test said, and what the floor has to survive. We will spec the system layer by layer and build the material list.
Latux Epoxy
2201 N Andrews Ave, Suite 108
Pompano Beach, FL 33069
(800) 413-1427
Monday to Friday, 8:00 AM to 5:00 PM.
Saturday by appointment.
Sunday closed.