Bare spots, fish eyes and craters in an epoxy coat

A flood coat that looked perfect when poured sometimes pulls back from small areas, leaving round bare patches, dimples or craters with raised rims. Woodworkers often call these fish eyes. The resin is not failing to cure; it is being pushed away from a spot it cannot wet.

The cause: something the resin will not stick to

According to ArtResin, a bare spot forms where a contaminant on the surface, most often oil, grease or wax, drives the resin away (ArtResin). It also lists wax, oil, plastics and silicone among materials that repel resin (ArtResin). EcoPoxy names grease, oil, wax and mold releases as residual contaminants that prevent bonding (EcoPoxy).

In practice, look for anything that can leave oil, grease, wax or silicone on the surface before the coat goes on, including mold release: it is designed to stop epoxy sticking, and EcoPoxy lists silicone among the materials epoxy will not stick to (EcoPoxy).

Prevention: surface preparation

• Clean before you coat. TotalBoat asks for a surface free of wax, grease and dust, wiped with acetone on a clean, lint-free rag and allowed to fully evaporate (TotalBoat).
• Abrade shiny surfaces. EcoPoxy recommends 220-grit abrasion to give the epoxy a textured surface to hold on to; rougher surfaces such as wood slabs do not need it (EcoPoxy).
• Keep release agents away from the work. Apply mold release to the mold only, and keep it off any surface you plan to coat.
• Keep the surface dry. EcoPoxy notes that moisture on the surface leads to blush and poor bonding (EcoPoxy).

The repair

ArtResin’s repair for bare spots (ArtResin):

1. Clean the area with isopropyl alcohol, or warm water and dish soap.
2. Let it dry completely.
3. Sand the whole surface with 80-grit sandpaper, wearing a dust mask.
4. Remove all sanding dust.
5. Pour a fresh coat of properly measured and mixed resin over the whole piece.

ArtResin does not recommend spot fixing, because a small patch is very hard to blend into the original coat, and says a full top coat gives the smoothest finish (ArtResin). Size the new coat with the flood coat calculator.

Not to be confused with

Looks like	Actually	Where to read
Small pits that rose and popped	Bubbles	Bubbles in epoxy
Greasy film over a hard coat	Amine blush	Amine blush
Rippled or scorched patches	Too much torch heat	Bubbles in epoxy