A fully cured epoxy coating that peels or flakes off the substrate is not a product defect — it is an adhesion failure, and the bond between the epoxy and the surface was almost always weaker than the internal strength of the cured film itself.
Why Delamination Is a Preparation Problem, Not a Product Problem
Adhesion requires two things working together: a clean surface and a sufficient mechanical profile, or roughness, for the epoxy to physically grip. Failing to provide either one leads directly to peeling under traffic, heavy dynamic loads, or thermal cycling, regardless of how well the epoxy itself was formulated.
Primary Cause One: Lack of Surface Profile (No Mechanical Key)
When the substrate is too smooth or dense for the epoxy to bond effectively, the coating rests on the surface instead of locking into it. On concrete, this typically means the weak, powdery surface layer known as laitance was never removed; on non-porous surfaces like metal or tile, it means no sanding or grinding was performed before application. High traffic, heavy dynamic loads such as vehicles, or repeated thermal cycling will eventually cause a sheet of unkeyed epoxy to peel off or flake in large pieces. The fix is to prepare the surface to the correct concrete surface profile for concrete substrates, or to scuff-sand aggressively — around 80 grit — for non-porous materials.
Primary Cause Two: Surface Contamination
Invisible contaminants create a chemical barrier between the epoxy and the substrate before the coating is ever applied. The most common culprits are oil and grease from fingerprints, cutting fluids, or silicone- and wax-based products; moisture, where water vapor pressure builds up underneath the coating on damp concrete and eventually pushes it off; and fine dust left over from grinding or sanding, which the epoxy bonds to instead of the floor beneath it. The result is a coating that only bonds in a few clean spots, producing localized flaking or blisters that later develop into full delamination once the coating is stressed by a load. The fix is thorough solvent cleaning with acetone or IPA after grinding, plus a moisture-vapor barrier primer on any damp concrete substrate.
Correct Surface Preparation for Prevention
Always grind or sand the substrate to create a rough, porous profile — for concrete, this means grinding until the aggregate is exposed and the surface reads completely dull, not glossy. After grinding, vacuum up all dust and wipe the surface with a lint-free cloth dampened with acetone or IPA to remove microscopic dust and oils; never use mineral spirits or any oil-based cleaner for this step, since they leave their own contaminant film behind. Always check concrete moisture content before coating, and apply a specialized moisture vapor barrier primer first if readings come back high.
Repairing Delamination That Has Already Occurred
Once delamination has occurred, treat the damaged area as a contaminated substrate that needs the same rigor as new work:
- Remove all failing material. Chip away or scrape off every piece of loose, peeling, or flaking epoxy until reaching firmly adhered material.
- Grind the exposed substrate. Aggressively grind or sand the newly exposed area and feather the perimeter of the existing coating to create a smooth transition.
- Clean and solvent-wipe. Decontaminate the entire repair area with acetone.
- Prime and recoat. Apply a fresh coat of epoxy primer to the exposed substrate for maximum adhesion, then apply the final topcoat to seal the repair.
Confirming Adhesion Before Full-Scale Application
Email Us if your team wants a pull-off adhesion testing protocol — a simple dolly-and-gauge test on a small cured sample area, performed before committing to a full floor or panel, catches marginal surface preparation before it becomes a large-scale delamination failure months later. For facilities weighing which coating chemistry best resists the heavy dynamic loading that most often triggers delamination, it’s worth comparing epoxy and UV-cure adhesive performance for heavy-duty repair applications.
Substrates that see repeated thermal cycling face an added complication beyond surface preparation alone: the coefficient of thermal expansion mismatch between the coating and the substrate generates its own cyclic shear stress at the bond line, which compounds any weakness left by inadequate surface prep.
Documenting a Repair So the Next Failure Is Easier to Diagnose
When delamination shows up, it’s worth recording exactly where it started and what the substrate looked like underneath — a corner-first failure pattern usually points to inadequate edge preparation, while a failure concentrated at the center of a large panel more often points to a moisture-vapor issue or a missed contamination spot mid-surface. Photographing the exposed substrate before regrinding, and noting whether the underside of the removed coating shows a glossy, unbonded surface versus a rough, torn one, tells you whether the original failure was adhesive (a clean break at the interface, meaning preparation was the issue) or cohesive (a break within the coating itself, meaning the material was undersized for the load). That distinction changes which fix actually matters: an adhesive failure calls for better surface preparation on the redo, while a cohesive failure calls for a thicker system or a higher-performance chemistry rather than just repeating the same application with cleaner technique.
Incure’s epoxy coating and primer systems are formulated for strong mechanical and chemical adhesion, but even the best-formulated system depends entirely on correct surface preparation to perform as designed. Contact Our Team for help specifying a primer and topcoat system suited to your substrate and service environment.
Visit www.incurelab.com for more information.