How to eliminate fish eyes and pin holes in epoxy coatings
Substrate contamination is the most common problem that causes fish eyes and pin holes in epoxy seal coats. Dust, dirt, wax, silicones, even the oil from your fingers when touching the part prior to sealing with epoxy will deter epoxy resins from laying flat and curing with a perfectly smooth surface.
Any contamination on the substrate (in the case of surfboards, the fiberglass lamination) will disrupt the surface tension and cause the epoxy to separate or pit. The epoxy will "run away" from contaminated area.
It all comes down to proper preparation for a nice smooth epoxy seal coat.
Top 5 tips to eliminating epoxy fish eyes, pin holes and separations:
1. Do your epoxy work in a clean, well ventilated environment with minimal air flow that may introduce contaminants to your work area.
2. Wipe the substrate with Denatured Alcohol (DNA) on a lint free rag to pick up most of the contaminants and oils that may be on your work piece. Let the denatured alcohol evaporate completely before applying an epoxy seal coat.
3. Wipe the work piece with an epoxy seal coat prep cloth. This will pick up any additional dirt or debris to leave a clean surface to apply the epoxy coat to.
4. Use a clean bristle brush, foam or nap roller, or squeegee to apply your epoxy coating.
5. Have the work piece the same temperature as the epoxy resin to avoid thermal shock and the resin quickly shrinking and orange peeling. If hot resin hits a cold substrate the rapid change in temperature will cause the resin to ripple and stop flowing correctly.
After preparing applying your epoxy seal coat it is important to avoid introducing contaminants into the "green" first stage epoxy cure.
1. Do not touch the wet epoxy seal coat - Walk away from it and come back about 10 minutes later to assess any inconsistencies in the coating. Even walking around the work piece may kick up dust and debris that will settle into your epoxy seal coat and cause a pin hole or fish eye. Just let the resin flow and flatten out for a while.
2. Come back to the fresh seal coat and assess if there are any small issues. Even with proper preparation and cleaning, fish eyes may occur due to environmental problems out of your control. If there are any issues in your epoxy seal coat simply drip some resin that is still remaining in your mixing bucket on the affected area and let the resin flatten out by itself and bond to the surrounding resin molecules.
3. Do not brush over inconsistent epoxy seal coat areas, that will most likely reduce the surface tension and result in a larger fish eye or separation. A drip of extra epoxy is all you need on the area to solve the issue.
In summary, proper epoxy resin seal coats are subject to your work space environment and your preparation efforts. Following the guidelines written above will greatly enhance the flatness, gloss, and uniformity of your epoxy coating.