Adhesion failure—where the epoxy coating or casting lifts, peels, or delaminates—is a frequent issue when working with non-porous materials (like metal or smooth plastic) or contaminated substrates. This failure is purely a surface bonding problem, usually caused by insufficient surface energy or an invisible chemical barrier.
The Root Causes of Poor Adhesion
Adhesion requires the liquid epoxy to “wet out” the surface and create mechanical and chemical anchor points. Failure occurs when these conditions are not met.
1. The Non-Porous Problem (Low Surface Energy)
- Slick Surfaces: Materials like polished metal, glass, glazed tile, or some high-density plastics (e.g., polyethylene, PTFE/Teflon) are so smooth that the liquid epoxy beads up or simply rests on the surface without penetrating. This prevents the formation of a mechanical key (a physical grip) and a strong chemical bond.
- The Result: The cured epoxy will lift easily, often peeling off like a sheet of plastic.
2. The Contamination Problem (The Barrier)
- Oils and Grease: This is the most common cause. Residue from fingerprint oils, cutting oils, hydraulic fluids, wax, tire shine, or release agents (silicone) acts as a chemical barrier. Epoxy cannot bond through these substances.
- Moisture: Water or high moisture content in the substrate or on the surface interferes with the hardener’s chemical reaction, leading to poor initial bond strength and eventual delamination.
- Laitance (Concrete): A weak, powdery, high-moisture layer on the surface of new concrete that has zero structural integrity for bonding.
Genuine Solutions for Maximum Adhesion
The solution requires meticulous surface preparation, often called profiling, to overcome the surface’s resistance.
1. Mechanical Profiling (Non-Porous Materials)
- Sand or Grind: For non-porous materials like metal, wood, or solid plastic, you must create a rough surface profile.
- Metals/Hard Plastics: Use 80-grit sandpaper or a grinder to aggressively scuff the entire surface. The goal is to create a profile deep enough for the epoxy to physically lock onto (mechanical keying).
- Concrete: Must be diamond-ground or shot-blasted to achieve a profile of CSP 2–3 (Concrete Surface Profile), removing all laitance and opening up the pores.
- No Gloss/Sheen: The surface must be completely dull and scratched. If you see any shiny areas, the surface is not profiled enough.
2. Decontamination (The Chemical Wipe)
- Pre-Cleaning: Use a mild detergent to remove heavy grease or oil.
- Solvent Wipe: After mechanical profiling, wipe the entire surface down thoroughly with Acetone or Denatured Alcohol (IPA) to remove all sanding dust, oils, and invisible residues. Do not touch the cleaned surface with bare hands before applying the epoxy.
- Avoid: Never use mineral spirits, paint thinners, or any product that leaves an oily residue.
3. Priming and Compatibility
- Use the Right Primer: For extremely challenging materials like highly polished aluminum, brass, or specialty plastics, use a specialized adhesion promoter or a compatible, low-viscosity epoxy primer specifically designed to bond to those difficult substrates.
- Moisture Mitigation: If concrete has a high moisture content (checked with a meter), a moisture-vapor-barrier epoxy primer is required before the final coat is applied. This prevents water vapor pressure from building up and pushing the cured epoxy off the substrate.