How to prepare a garage floor for epoxy
SFL Epoxy is a guide run by Terragroupe, LLC. We do not install anything and we are not booking jobs yet.
Good prep means a clean, dry, sound slab with a rough surface the coat can grip. The manufacturer data sheets we read call for grinding or shot-blasting, a moisture test and repairs before any coating 1. A coat over a slab that fails those checks is set up to peel.
SFL Epoxy is a guide run by Terragroupe, LLC. We do not install anything and we are not booking jobs yet.
Last reviewed October 18, 2026 against the cited sources.
Updated . Sources
Start with the surface
Oil, paint and sealers get in the way of a bond. The sheets we read call for removing sealers and oil, then opening the surface by grinding or shot-blasting 1.
Grinding uses a diamond wheel on a machine. Shot-blasting throws steel shot at the slab. Both leave a rough profile that the coat can grip. A smooth, power-troweled or sealed slab gives a coat very little to hold.
Test the slab for moisture
Ground moisture can move up through a slab on the ground. A plastic sheet directly under the slab is the recommended barrier, but you cannot see it from the garage 2.
The sheets set a limit on slab moisture, read with a meter, and the limit belongs to the product named in your scope 1. Ask to see the reading before any coat goes on. A damp patch, white powder or a musty smell is a reason to test first.
Repair cracks and broken areas
Cracks, chips and spalled areas need repair before coating. A coat will show a crack through it, and it can open along a crack that moves.
A crack that keeps widening, or a slab that has sunk, is a structural question. That is outside this guide. Ask your building department who may assess it.
Old coatings and failed kits
A coating that is lifting has to come off, along with the loose edges around it. Then the slab under it needs the same moisture test as bare concrete.
A coating that is still bonded may stay, but only if the new product's sheet allows it. Ask the installer how they check that the old layer is bonded.
What to ask for in the written scope
- The prep method: grinding or shot-blasting.
- How oil, sealers and old coatings are removed.
- The crack and spall repair.
- The moisture reading, and what happens if it fails.
- The wait before cars go back in.
Read the guide on why coatings peel for the failure side of the same story.
Facts used in this guide
| Fact | Value | Source |
|---|---|---|
| Polyaspartic topcoat data sheet requires substrate at least 5 F above dew point and max ambient RH of 75% during application and curing. | 5 F margin; RH <= 75 F / percent RH | [1] June 10, 2021 |
| Epoxy smooth-finish coating data sheet: max RH 85% during application and cure; substrate at least 5 F (3 C) above dew point; substrate 50-86 F; concrete moisture <= 4% by Tramex meter; no vehicle load until fully cured. | RH <= 85; moisture <= 4; substrate 50-86 percent RH / percent by mass / F | [3] 2026-06 |
| Polyaspartic topcoat at 68 F: foot traffic ~4 h, light traffic ~8 h, full cure ~5 days; marketed for enhanced hot-tire-marking resistance and excellent UV resistance. | 4 h / 8 h / 5 days hours / days | [1] June 10, 2021 |
| Garage-market polyaspartic base coat data sheet: apply 30-90 F, tack-free 2-4 h, vehicles after 24 h at 72 F / 50% RH, recoat 2-12 h, UV stable. | vehicles 24 h hours | [4] 2025 (Version 1; Rev 11/21) |
| Ground moisture can move up through slab-on-grade concrete; a plastic sheet directly under the slab is the recommended barrier, and Building Science argues Florida slabs fare better than California's because of that practice. | n/a | [2] May 26, 2008 |
Garage Floor Readiness Score
Answer each question. The score shows how much needs sorting out before a coating, and which answers added the most. It is a starting point, not a price or a promise.
Start the Garage Floor Readiness ScoreSFL Epoxy is a guide run by Terragroupe, LLC. We do not install anything and we are not booking jobs yet.
Questions people ask
How do you prepare concrete for epoxy?
Clean the slab, remove oil and sealers, open the surface by grinding or shot-blasting, repair cracks, and test the slab for moisture 1. Each step goes in the written scope.
Do I need to grind my garage floor?
The data sheets we read call for grinding or shot-blasting 1. Skipping that step leaves a smooth surface that a coat grips poorly.
Can I put epoxy over old paint?
Loose or lifting paint has to come off. Paint that is firmly bonded may stay only if the new product allows it. Ask the installer to name the check they use and to write it into the scope.
Sources
- Sikafloor-515 polyaspartic topcoat data sheet (manufacturer), June 10, 2021
- Building Science Corporation, BSI-003 Concrete Floor Problems (Lstiburek), May 26, 2008
- Sikafloor-261 CA Product Data Sheet (fiche technique), 2026-06
- ArmorGarage Polyaspartic Floor System TDS (ArmorPoly 80), 2025 (Version 1; Rev 11/21)