Problem Solver (FAQ)

This guide is designed to help identify and prevent potential problems associated with using WEST SYSTEM® Epoxy. If the solutions described here do not resolve the problem, contact our technical staff.

Problem Table of Contents
The epoxy mixture has not cured after the recommended cure time has passed.
Clear coating turned cloudy.
Bond failure.
Waxy film appears on surface of cured epoxy.
Hardener has turned red after several years storage.
Runs or sags in coating.
Fairing compound (epoxy/407 or 410 mixture) sags and is difficult to sand.
Paint or varnish will not set up over epoxy.
Epoxy became very hot and cured too quickly.
Bubbles formed in coating over porous material (bare wood or foam).
Pinholes appear in epoxy coating over abraded fiberglass or epoxy.
Fish-eyeing in coating.

The epoxy mixture has not cured after the recommended cure time has passed

POSSIBLE CAUSES & SOLUTIONS

Off ratio: Too much or too little hardener will affect the cure time and thoroughness of the cure.

  1. Remove epoxy. Do not apply additional material over non-curing epoxy. See Clean Up & Removing.
  2. Check correct number of pump strokes: Use equal strokes of resin and hardener. DO NOT add extra hardener for faster cure!
  3. Check for correct pump (5:1 or 3:1 ratio) and pump group size (Group B resin and Group B hardener).
  4. Check pump ratio (see 300 Mini Pump Instructions). See Dispensing & Mixing.

Low temperature: epoxy mixtures cure slower at low temperatures.

  1. Allow extra curing time in cool weather.
  2. Apply heat to maintain the chemical reaction and speed the cure.
  3. Use 205 Fast Hardener, designed to cure at lower temperatures.
  4. See Cold Temperature Bonding.

Insufficient mixing.

  1. Remove epoxy. Do not apply additional material over non-curing epoxy. See Clean Up & Removing.
  2. Mix resin and hardener together thoroughly to avoid resin-rich and hardener-rich areas. See Dispensing & Mixing.
  3. Only add fillers or additives after resin and hardener have been thoroughly mixed.

Incorrect products.

  1. Remove epoxy. Do not apply additional material over non-curing epoxy. See Clean Up & Removing.
  2. Check compatibility of resin and hardener. Resin will not cure properly with other brands of hardener or with polyester catalysts.

 

Bond failure

POSSIBLE CAUSES & SOLUTIONS

Insufficient cure.

See above.

Resin starved joint: epoxy has wicked into porous surfaces leaving a void at the joint.

Wet out bonding surfaces with neat epoxy mixture before applying thickened epoxy. Re-wet very porous surfaces and end grain. See Bonding & Clamping.

Contaminated bonding surface.

Clean and sand the surface following the procedure in the Surface Preparation. Sand wood surfaces after planing or joining.

Bonding area too small for the load on the joint.

Increase bonding area by adding fillets, bonded fasteners or scarf joints. See Bonding & Clamping.

Too much clamping pressure squeezed epoxy out of the joint.

Use just enough clamping pressure to squeeze a small amount of epoxy from the joint. See Bonding & Clamping.


Clear coating turned cloudy

POSSIBLE CAUSES & SOLUTIONS

Moisture from condensation or very humid conditions reacts with components in uncured hardener.

  1. Apply moderate heat to partially cured coating to remove moisture and complete cure. See Out-Gassing caution in Epoxy Chemistry.
  2. Use 207 Special Clear Hardener for clear coating applications and for bonding thin veneers where epoxy may bleed through to the surface.

Entrapped air from aggressive roller application.

  1. Apply coating at warmer temperature–epoxy is thinner at warmer temperatures.
  2. Apply epoxy in thin coats.
  3. Apply moderate heat to release trapped air and complete cure. See Out-Gassing caution in Epoxy Chemistry.

Waxy film appears on the surface of cured epoxy

POSSIBLE CAUSES & SOLUTIONS

Amine blush forms as a result of the curing process.

  1. 1. Blush is water soluble. Remove with water. See Special Preparation—Cured Epoxy in Surface Preparation.
  2. 2. Use 207 Special Clear Hardener. 207 is blush free.

Hardener has turned red after several years storage

POSSIBLE CAUSES & SOLUTIONS

Moisture in contact with hardener and metal container.

Red color is a normal condition. It will not affect epoxy handling or cured strength. Avoid using for clear coating or exposed areas where color is not desired.


 

Runs or sags in coating

POSSIBLE CAUSES & SOLUTIONS

Epoxy applied too thick.

  1. Use 800 Roller Covers and roll the coating out into a thinner film. A thin film will flow out much smoother than a thicker film after it is tipped off with the foam roller brush.
  2. Warm the epoxy to thin it or apply the coating at a warmer temperature. See Cold Temperature Bonding.

See Barrier Coating.

Coating curing too slowly.

  1. Apply the coating at a warmer temperature.
  2. Warm the resin and hardener before mixing to speed the cure in cool weather.
  3. Switch to a faster hardener such as 205 Fast Hardener if possible.

See Controlling Cure Time under Epoxy Chemistry.


 

Fairing compound (epoxy/407 Low-Density or 410 Microlight mixture) sags and is difficult to sand

POSSIBLE CAUSES & SOLUTIONS

Fairing material is not thick enough.

  1. Add more filler to the mixture until it reaches a “peanut butter” consistency; the more filler added, the stiffer and easier it will be to sand.
  2. Allow the wet-out coat to gel before applying the fairing material to vertical surfaces.

See Fairing.


 

Paint or varnish will not set up over epoxy

POSSIBLE CAUSES & SOLUTIONS

Epoxy not completely cured.

Allow the final epoxy coat to cure thoroughly. Allow several days if necessary for slow hardeners at cooler temperatures. Apply moderate heat to complete the cure if necessary. See Controlling Cure Time under Epoxy Chemistry.

Paint incompatible with epoxy.

  1. Use a different type of paint. Some paints and varnishes may be incompatible with some hardeners. If unsure, test for compatibility on a coated piece of scrap material.
  2. Use 207 Hardener. It is compatible with most paints and varnishes.

Epoxy surface not thoroughly prepared.

Remove the amine blush and sand the surface thoroughly before applying paints or varnishes. See Final Surface Prep.


 

Epoxy became very hot and cured too quickly

POSSIBLE CAUSES & SOLUTIONS

Batch too large.

  1. Mix smaller batches.
  2. Transfer the mixture to a container with more surface area immediately after mixing.

See Understanding Cure Time under  Epoxy Chemistry, and Dispensing & Mixing.

Temperature too warm for the hardener.

Use 206 Slow Hardener or 209 Extra Slow Hardener in very warm weather.

Application too thick.

Appy thick areas of fill in several thin layers.


 

Bubbles formed in coating over porous material (bare wood or foam)

POSSIBLE CAUSES & SOLUTIONS

Air trapped in the material escapes through coating (out-gassing) as the material’s temperature is rising.

  1. Coat the wood as its temperature is dropping—after warming the wood with heaters or during the later part of the day.
  2. Apply a thinner coat, allowing air to escape easier.
  3. Tip off the coating with a roller cover brush to break bubbles. See Barrier Coating.

See Out-Gassing caution in Epoxy Chemistry.


Pinholes appear in epoxy coating over abraded fiberglass or epoxy

POSSIBLE CAUSES & SOLUTIONS

Surface tension causes epoxy film to pull away from pinhole before it gels.

After applying epoxy with an 800 Roller Cover, force epoxy into pinholes with a stiff plastic spreader held at a low or nearly flat angle. Re-coat and tip off coating after all pinholes are filled.


Fish-eyeing in coating

POSSIBLE CAUSES & SOLUTIONS

Contamination of the coating or surface or improper abrasion for the coating.

  1. Be sure the mixing equipment is clean. Avoid waxed mixing containers.
  2. Be sure the surface is properly prepared. Use proper grit sandpaper for the coating, e.g., 80-grit for epoxy. See the paint or varnish manufacturer’s instructions for proper surface preparation. After the surface is prepared, avoid contamination—fingerprints, exhaust fumes, rags with fabric softener (silicone). Coat within hours of preparation. After wet sanding, rinse water should sheet without beading (beading indicates contamination). Wipe with appropriate solvent and re-rinse until rinse water no longer beads.

 

To contact our Technical Staff phone 866-937-8797 weekdays between 9:00 AM and 5:00 PM EST or Email us.