Technical Problem-Solving

Why Your Epoxy Coating Is Blushing — Causes & Fixes

Epoxy blushing — the formation of a whitish, waxy, or greasy film on the surface of curing or freshly cured epoxy coatings — is one of the most common coating failures encountered on GCC industrial and marine projects. It is particularly prevalent in the UAE and Saudi Arabia during the summer months, when coastal humidity rises rapidly overnight even as daytime temperatures soar. Left untreated, blushing leads to adhesion failure of subsequent coats, reduced chemical resistance, and premature coating system failure.

Root Causes of Epoxy Blushing

Cause	Mechanism	Most Common In
High ambient humidity during curing	Amine hardener reacts with moisture and CO₂ instead of epoxy resin	UAE and KSA coastal areas at night, summer months
Using polyamide hardeners in humid conditions	Polyamides are highly susceptible to CO₂ reaction; primary amine groups react with CO₂ fastest	Projects specifying standard polyamide epoxy systems in coastal zones
Low temperature during cure	Slows epoxy crosslinking, leaving more free amine available to react with CO₂	Night-time application in cooler seasons; air-conditioned spaces
Excess hardener (NCO/OH or NH/epoxy ratio off)	Excess free amine is more available to blush	Poorly controlled mixing; inaccurate volumetric ratios
Applying over dew or condensation	Moisture on substrate reacts with hardener at the interface	Early morning application before substrate reaches dew point + 3°C
Thin film application	High surface area relative to volume accelerates amine migration to surface	Thinned epoxy primers applied below minimum DFT

How to Identify Epoxy Blushing

• Visual: Whitish, milky, or waxy sheen on the surface of the cured coat. Can look like moisture or a fine crystalline deposit.
• Touch: The surface feels greasy or slippery, unlike a normal cured epoxy which should feel hard and dry.
• Water test: Water beads more aggressively than usual on a blushed surface.
• Adhesion test: Cross-hatch adhesion test (ISO 2409) on the next coat will show poor adhesion, often failing at 3–4 rating or worse.

Raw Material Solutions — Prevention at the Formulation Level

The most effective approach is selecting the right hardener for your application environment:

• Phenalkamine hardeners: Specifically designed for high-humidity and marine applications. React much faster with epoxy resin than with CO₂, dramatically reducing blushing tendency. Use for UAE coastal, offshore, or Saudi Arabia applications where overnight humidity may exceed 80% RH.
• Cycloaliphatic amine hardeners: Good blush resistance, faster cure than polyamide. Suitable for moderate humidity conditions. Produce harder, more chemical-resistant films than polyamide.
• Mannich base hardeners: Accelerated cure, good performance in low-temperature or high-humidity conditions. Used where pot life constraints and humidity resistance must both be met.
• Avoid polyamide hardeners for exterior or coastal GCC applications in summer. Reserve polyamide for interior applications where humidity is controlled.

Application-Level Prevention Measures

• Monitor relative humidity and surface temperature continuously during application. Apply only when RH is below 85% and surface temperature is at least 3°C above dew point.
• Avoid overnight curing without temporary shelter in coastal UAE and Saudi Arabia from May to October, when humidity swings from 20% RH at 3 PM to 85%+ at 4 AM.
• Use a faster-curing hardener or add an accelerator to ensure the epoxy crosslinks before CO₂ reaction competes.
• Apply at the minimum recommended DFT — never thin below the manufacturer's minimum or apply thinner than the specified DFT.

Raw Material Sourcing for Blush-Resistant Epoxy Systems

Raykem supplies liquid epoxy resins (Bisphenol A) and a full range of hardeners to paint manufacturers across the UAE and Saudi Arabia, including polyamide, polyamidoamine, phenalkamine, cycloaliphatic amine, and aliphatic amine hardeners. Our technical team can advise on the optimal hardener selection for your specific application environment, DFT requirement, and pot life constraint. Contact our Dubai or Riyadh office for samples, technical data sheets, and formulation support.