You cannot install flake epoxy over sealed or polished concrete without removing the existing surface treatment first. Both sealers and polishes create a tight, low porosity surface that epoxy cannot grip. The fix is mechanical: a diamond grind through the sealer or polish until you reach raw, profiled concrete at CSP 2 to CSP 3. Chemical strippers work for thin acrylic sealers but not for densifiers or polished concrete. Plan on 4 to 8 hours of grinder time for a 400 sq ft garage, about $90 in rental, and $50 in tooling.
Sealers and Polishes Block Epoxy Bond
Concrete sealers come in two main types, and both are problems for coating.
- Topical sealers (acrylic, urethane, water based) sit on top of the slab as a thin 1 to 4 mil film. They are designed to repel water, oil, and stains. They also repel epoxy.
- Penetrating sealers (silane, siloxane, lithium silicate densifier) soak into the top 1/16 to 1/4 inch of concrete and create a hydrophobic or hardened layer. They do not form a visible film but they close the surface porosity epoxy needs to mechanically lock into.
Polished concrete is a step further. The grinding and polishing process closes nearly all surface porosity, the densifier hardens the top layer, and the polish guards seal it. The result is a beautiful floor that has approximately the same bond profile as glass. Epoxy will sit on it for a few weeks, then peel off in sheets.
How to Identify What You Have
If you do not know what is on your slab, run two tests.
- Water bead test. Drop a tablespoon of water on the floor in three spots. If it beads up and sits on the surface for over 60 seconds, you have a hydrophobic sealer or polish. If it soaks in within 10 seconds, you have raw or lightly treated concrete.
- Acetone wipe. Wipe a small area with a rag soaked in acetone for 30 seconds. If the rag comes back with color, residue, or a slight tackiness, you have a topical sealer that acetone is dissolving. If the rag is clean and the floor looks unchanged, you either have raw concrete or a penetrating sealer or polish.
Polished concrete is usually obvious. It has a mirror or satin sheen, often with visible aggregate exposed at the surface. If you can see your reflection in the floor under good light, it is polished. Builder grade slabs that have only been hard troweled (not polished) can also look slightly glossy but are not sealed. The water bead test sorts the two.
Removal: Topical Sealers
Acrylic and urethane topical sealers can be removed two ways.
Chemical stripper: Works for thin acrylics under 3 years old. Use a methylene chloride free stripper, apply 1/8 inch thick, cover with paper, wait 2 to 4 hours, scrape and rinse. Then grind to set profile. Cost: about $80 per 100 sq ft in stripper. Total time 6 to 8 hours for a 400 sq ft garage.
Diamond grind: Works for everything. Use 25 to 30 grit metal bond diamonds, run a single pass to remove the sealer, then a 60 to 80 grit resin pass to set profile. Cost: $90 grinder rental, $50 to $70 in diamonds. Total time 3 to 5 hours.
Grinding is faster, cheaper, and gives you the right profile in one step. Use stripper only if you have a sealer that resists grinding (some thick urethanes load up the diamonds badly), or if you are working in a small area where the grinder is overkill.
Removal: Penetrating Sealers and Densifiers
Chemical strippers do not work on penetrating sealers or lithium silicate densifiers. The treatment is in the concrete, not on it. Grinding is the only option.
Use 16 to 25 grit metal bond diamonds, and plan to remove 1/16 to 1/8 inch of concrete to get below the sealer depth. A standard 60 grit resin pass after the initial grind sets the profile. Expect tooling to last about half as long as it would on raw concrete, because densified slabs are harder than untreated concrete.
Total time for a 400 sq ft garage: 5 to 7 hours. Total cost: $90 rental, $60 to $90 in diamonds. If your slab has been densified multiple times (common in commercial conversions to residential), plan on a second metal bond pass and longer total time.
Removal: Polished Concrete
Polished concrete is the toughest case. The surface has been densified, ground to a high polish (often 800 to 3000 grit), and sometimes coated with a guard product on top. You are removing about 1/16 inch of densified, hard concrete.
- Start with 16 grit metal bond diamonds to break through the polish.
- Run a 30 grit pass to remove the densified layer.
- Finish with a 60 to 80 grit resin pass for profile.
Plan on 6 to 10 hours of grinder time and 2 sets of metal bond diamonds for a 400 sq ft floor. If the polish is fine (over 1500 grit) or the densifier is heavy, you may need shot blasting instead. Shot blasting rental runs $300 to $500 a day but cuts the time to under 90 minutes.
Profile Check Before You Coat
After grinding, the floor should look matte, uniform, and slightly textured. Run your fingertips across it. You should feel the equivalent of 60 grit sandpaper. If any area still has a sheen or feels smoother than the rest, hit it again. The whole floor needs the same CSP 2 to CSP 3 profile.
A quick visual check: pour a tablespoon of water on the prepped area. It should soak in within 10 seconds across the entire surface. If it beads anywhere, you missed a spot, and that spot will fail. Mark any failed area with chalk, hit it with the hand grinder, and retest. This is the single highest leverage step in the entire prep process. Skipping it costs you the whole floor.
When Removal Is Not Worth It
If you have a high quality polished concrete floor you love and you only want flake in part of the garage (a workshop corner, a parking area), consider a different approach. Mechanically fasten a vinyl flake mat or a snap together polypropylene tile system over the polish. No grinding, no chemical bond, fully reversible. Costs more per sq ft but preserves the polished surface underneath.
If the sealer or polish is failing anyway, remove and coat. You get a fresh, decorative finish with a 15 plus year service life and the prep cost is under $250 for materials. A failing sealer typically shows up as flaking, yellowing, or uneven sheen. Once the existing surface looks bad enough to bother you, it is bad enough that removal is the right call.
Get the Slab Ready
Sealed and polished slabs add about one day to the project. Do the grind, set the profile, vacuum twice, do the water bead check, and you are at the same starting line as someone with raw concrete. From there, the Custom Blend Builder lets you pull from 140 Torginol colors if the standard catalog does not have your exact look. The floor below dictates the prep. The flake on top is the fun part.
