Short answer: Epoxy peels when it never bonded properly to the concrete. The usual causes are a smooth or contaminated surface, moisture coming up through the slab, coating in the wrong temperature or humidity, and driving on the floor before it has cured. Almost all of these come down to preparation and testing before the first coat.
The main causes of peeling
1. The surface was too smooth or dirty
Coatings need a rough, open surface to grip. Euclid Chemical's installation instructions call for a concrete surface profile of CSP 2 to 5 on the International Concrete Repair Institute scale, "preferably by mechanical means" such as grinding. Oil, sealers, old paint and curing compounds stop the bond and must come off first.
2. Acid etching was used and not neutralized
Acid etching is a cheaper preparation method. If it is used, Euclid's instructions require the surface to be neutralized and rinsed. Etching also cannot remove sealers or oil the way grinding can.
3. Moisture pushed the coating off
Water vapour moving up through a slab can build pressure under the coating. Testing tells you whether it is a risk. Euclid sets the threshold for a moisture-mitigating system at 85% relative humidity (ASTM F2170 probe test) or 3 lbs per 1,000 sq. ft. per 24 hours (ASTM F1869 calcium chloride test).
4. The slab was too new
New concrete must be at least 28 days old before coating, according to the same instructions.
5. Condensation during application
If the surface is within 3°C (5°F) of the dew point, moisture can condense on the slab while the coating goes down. That is a particular risk in cool, humid GTA garages in spring and fall.
6. Hot tires too soon
Parking before the coating has fully cured can let warm tires pull it up. Follow the product's stated cure time before vehicle traffic.
What good preparation looks like
- Inspect and test: look for cracks, spalling, stains and old coatings; test moisture where there is any doubt.
- Grind or blast the surface to the profile the product requires.
- Repair cracks, spalls and holes, then grind repairs flush.
- Vacuum thoroughly.
- Check temperature and dew point before mixing.
- Apply within the recoat windows on the data sheet.
Our customers notice this step. One wrote that their concrete "needed quite a bit of work beforehand" before the flake coating went down; another said the team explained "what repairs needed to be done first".
Red flags in a quote
- No mention of how the concrete will be prepared
- A one-coat kit product sold as a professional floor
- No moisture testing on an older or below-grade slab
- No cure time stated before you can park
Worried about an old or damaged garage floor? We will look at your concrete, explain what needs repair first and give you a written estimate. Epoxy floors are available across the GTA, including Vaughan.
REQUEST A FREE ESTIMATERelated: what epoxy garage floors cost and epoxy vs. polyaspartic.
Sources: Euclid Chemical: EUCOPOXY TUFCOAT installation instructions (PDF) · KTA-Tator: Measuring the surface profile of prepared concrete