How-To
How to Prep Concrete for Epoxy (The Step That Decides If It Lasts)
Eighty percent of epoxy floor life is decided before resin hits the slab. Here's the real prep sequence: grind, moisture test, repair, then coat — and what happens when a crew skips it.
Prep is the job. The resin is the last 20 percent. If a crew rolls epoxy over dust, paint, or a wet slab, the floor will look finished and then peel. That is not a product failure. That is a skipped grind.
Elite Epoxy Design diamond-grinds, moisture-tests, and repairs before any base coat. If you are hiring anyone else, ask them to describe that sequence out loud. Vague answers are a warning.
The sequence that actually works
1. Look at the slab before you quote
Oil halos, spalls, paint, prior DIY kits, control joints, and age of the house. A 1960s Metro Detroit garage without a vapor barrier is a different job than a 2018 pour. Local context is in garage floor coating in Metro Detroit.
2. Moisture test
Calcium chloride (ASTM F1869) or a calibrated meter. If vapor is high, a standard film will blister. Details in concrete moisture testing before epoxy.
3. Diamond grind
Mechanical grinding to a CSP-2 / CSP-3 profile. You should see aggregate, not laitance. Acid etch does not replace this on a garage that sees hot tires.
4. Repair
Route and fill cracks. Patch spalls with a polymer-modified material. Degrease oil until water sheets, not beads.
5. Then coat
Base, flake or metallic, polyaspartic topcoat. Garage floors and warehouses use the same idea with different thickness.
What “prep” is not
- Sweeping and a solvent wipe
- Painting over old epoxy “to refresh it”
- One coat of primer on glossy paint
- Skipping grind because the slab “looks clean”
Clean is not profile. Coatings need tooth.
DIY vs professional grind
A rental grinder can work on a small shop if you know dust control and you still moisture-test. Most homeowners under-grind edges and around bolts. Those are the first places a coating lifts. If the garage is your daily parking, hire a crew that owns the machine and the vacuum.
After prep: chemistry still has to match the room
UV through a garage door yellows cheap epoxy. Michigan salt wants a tight topcoat. Compare systems in polyaspartic vs epoxy vs polyurea. Prep will not save the wrong film in a sunny, salty bay.
FAQ
Do I need to grind concrete before epoxy?
Yes. Diamond grinding opens a profile the coating can lock into. Acid etch and TSP are not a substitute on a garage or commercial slab.
Can you epoxy over paint or old coating?
Only if it is fully bonded. We test adhesion. Failed film comes off. Coating over peel is how you get a bigger peel.
How long does prep take?
On a typical two-car garage, grinding and repair are a large part of the day. The coat is the shorter part if the slab cooperates.
What moisture reading is too high?
If calcium chloride or meter readings are above the system limit, we add a moisture-mitigating primer or we do not coat. Guessing is how blisters start.