▽ +09.00Technical article · Floors
Why epoxy floors fail: peeling, blistering and cracking
An epoxy floor is a thin layer that depends completely on the slab below it. Most failures are not the resin’s fault: they start with moisture, a weak surface, a system that does not suit the use, or the conditions on the day it was laid.
03minutes read
- Topic
- Floors
- Sections
- 06
- References
- 04
- Published
- Publisher
- Prime Shield — engineering content
Moisture from the slab
Slabs on grade can hold moisture long after they look dry. Moisture rising through the slab can push off a dense resin layer or cause osmotic blistering — fluid-filled blisters under the coating. Slab moisture is therefore measured before coating by the method the system requires, such as in-situ relative humidity probes (ASTM F2170) or the calcium chloride test (ASTM F1869), against the TDS limits; where moisture is high, a moisture-tolerant primer or a different system may be specified.
A weak or smooth surface
Resin bonds to the top millimetres of the slab. Laitance, curing compounds, oil, old coatings and a glassy power-trowelled surface leave nothing sound to bond to. Mechanical preparation — shot blasting, diamond grinding or scarifying — removes them and gives a profile, often specified as a concrete surface profile (CSP) per the ICRI 310.2R guideline. Pull-off tests (ASTM D7234) confirm the surface strength where specified.
The wrong system for the use
- A thin coating where vehicles, pallet trucks or impact need a thicker system.
- No slip resistance where the floor gets wet or oily.
- A system that does not resist the chemicals, cleaners or hot water in use.
- Aromatic epoxy in sunlight: yellowing and chalking — a UV-stable top coat may be specified.
- Coating over cracks and joints without detailing: they reflect through.
On the day: mixing and conditions
- Wrong ratio or poor mixingSoft or sticky patches that never cure.
- Pot life exceededMaterial spread after it began to gel.
- A cold slab or high humidityA slow cure and a greasy surface film (amine blush) that ruins the next coat’s bond.
- Slab temperature near the dew pointCondensation under the coating; the slab is kept above the dew point by the margin the TDS sets.
- OutgassingPinholes when the slab is coated while it warms up.
Reading the failure
| What you see | Usual cause | Check |
|---|---|---|
| Coating peels with no concrete attached | Contamination or no profile | Preparation records; the underside of the flake |
| Coating peels with a thin layer of concrete | A weak surface or moisture | Pull-off test, moisture readings |
| Blisters with liquid | Osmotic blistering, moisture | Moisture testing, blister contents |
| Pinholes | Outgassing, air in the mix | Application temperature records |
| Sticky or soft patches | Mix ratio or mixing | Batch records |
| Cracks in lines | Slab cracks or joints not detailed | The slab joints below |
How it is avoided
- Moisture tests recorded before priming.
- Mechanical preparation to the specified profile.
- A system chosen for the traffic and the chemicals.
- Joints and cracks detailed.
- Conditions logged on the day: air and slab temperature, humidity and dew point.
- Thickness or consumption checked per area.
References
Standards and guides on the subject — named to show what they cover, not to claim that any product complies.
- ASTM F2170Relative humidity in concrete slabs using in-situ probes.
- ASTM F1869Moisture vapour emission rate of a slab using calcium chloride.
- ICRI 310.2RSelecting and specifying concrete surface preparation for coatings, overlays and repair.
- ASTM D7234Pull-off adhesion strength of coatings on concrete using portable testers.
General educational content; final values and requirements follow the manufacturer’s TDS and the approved project specification.
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