Why an Epoxy Floor Is Peeling: Causes and How to Read the Back of the Flake

An epoxy floor looks glossy on handover day. A few months later a small flake lifts at the garage door or along a wall, and it spreads until whole sheets come away. The failure is frustrating because it seems sudden, but it is rarely random. In most cases the cause was already there before the first coat, in the concrete or in the conditions on the day of application.

What matters is that the repair depends entirely on the cause. Anyone who simply repaints without diagnosing will repeat the same failure. So we start with the causes, then explain how to read a detached flake to find out which one is behind your problem.

What causes an epoxy floor to peel?

1. Concrete moisture and vapour pressure

Concrete is porous and holds water, especially ground-bearing slabs in contact with soil and recently poured slabs. Epoxy forms a film that is largely vapour-tight, so if moisture rises from below it collects under the coating and pushes it off. ASTM D4263 describes the plastic sheet method for indicating moisture in concrete before coating, ASTM F1869 measures the moisture vapour emission rate over 24 hours, and ASTM F2170 measures relative humidity inside the slab with probes.

2. Inadequate surface preparation

The surface of a poured slab carries a thin, weak layer of cement and dust called laitance. Epoxy bonds to it well, but the laitance itself then separates from the concrete below. The Sikafloor-263 SL data sheet calls for mechanical preparation of the concrete by blasting or scarifying to remove this layer and leave an open-textured surface. The concrete surface profile (CSP) guide explains that grinding gives a relatively smooth profile, while shot blasting gives a rougher profile suited to thicker systems.

3. Oil and grease contamination

In garages and workshops, concrete soaks up oil over the years. Light surface grinding does not remove it from depth, so the oil migrates back to the surface and blocks adhesion. The problem usually shows up in distinct patches that match where vehicles park.

4. Amine blush between coats

Sherwin-Williams explains that amine blush results from the amine component of the epoxy reacting with moisture and carbon dioxide in the air, leaving a greasy or whitish film on the surface. That film acts as a bond breaker between coats, so the upper coat separates from the one beneath. The same source warns against fuel-burning heaters, because they add moisture and carbon dioxide to the air.

5. Application outside the permitted conditions

The Sikafloor-264 data sheet sets an air temperature between +10 and +35°C, relative humidity not above 80%, and a surface temperature at least 3°C above the dew point. In Jeddah and Dammam in summer these limits are easy to cross at night, and water condenses on the surface while the coating is curing.

6. Coating over old paint or a previous layer

Some floors get epoxy over old floor paint, a curing compound or a wax polish to save the cost of removal. The epoxy then bonds not to the concrete but to that old layer, so its adhesion is limited by the strength of that layer. If it is weak or incompatible, both layers peel together. The fix is to remove the old layer mechanically, or to prove by testing that it is sound and compatible before applying.

How can you tell the cause from the back of the detached flake?

Pick up a loose flake and look at its underside. Where the separation happened tells you the weakest layer in the system, which is also the principle behind pull-off tests under ASTM D7234, where failure occurs at the weakest plane.

How is peeling repaired, depending on its cause?

1. 1

   Remove the weak areas

   Every loose area, and any part that sounds hollow when tapped, is removed, and the limit of sound adhesion is marked before any repair.

2. 2

   Measure the moisture

   A plastic sheet, calcium chloride or in-slab humidity probe test is carried out. If moisture is high, a primer made for damp concrete and specified by the manufacturer is chosen, or the application is postponed.

3. 3

   Prepare mechanically and correctly

   Grinding or shot blasting gives the texture the system data sheet asks for, and dust is removed by vacuum, not by sweeping.

4. 4

   Deal with oil

   In severe patches the deeply contaminated concrete is removed, or treated as the manufacturer recommends, and adhesion is tested before coating.

5. 5

   Run a pull-off test

   Confirm the concrete meets the minimum in the data sheet, such as 1.5 N/mm² in the Sikafloor data sheets cited here.

6. 6

   Apply within the conditions

   Temperature, humidity and dew point are measured and recorded, recoat windows are respected, and if amine blush appears it is washed with water and detergent, then dried.

If the problem is in the concrete itself, such as cracks, crumbling or obvious weakness, the repair starts with concrete repair before any coating goes on. To understand the material and its limits, read our epoxy material guide.

How do you avoid peeling on a new floor?

With our epoxy flooring service, these measurements are documented before application, as part of the contracting work Azl carries out. If the peeling is in a garage specifically, load, oil and hot-tyre considerations are covered in our guide to epoxy garage floor coating.