While WEST SYSTEM Epoxy creates an excellent moisture barrier by itself, 422 Barrier Coat Additive is a proprietary blend designed to further improve cured epoxy’s moisture exclusion effectiveness. 422 is used as a barrier coating additive to help prevent gelcoat blistering in polyester fiberglass boats. 422 also increases the epoxy’s abrasion resistance. Cures to a light gray color.
Add to mixed resin/hardener at the rate of 15 to 20% by volume or 3 tablespoons per 8 fl oz of epoxy. When using 300 Mini Pumps with 5:1 ratio epoxy mixtures, 10 strokes of 105 Resin and 10 strokes of 205 or 206 Hardener yields 8 fl oz. of epoxy; for 3:1 ratio epoxy mixtures, 9 strokes of 105 Resin and 9 strokes of 207 or 209 Hardener yields 8.1 fl oz. of epoxy.
A 16 oz can of 422 Barrier Coat Additive will modify approximately half a gallon of mixed epoxy.
Repairing individual gelcoat blisters from time to time and improving ventilation may head off the problem and avoid the need for a full-blown barrier job. For step-by-step instructions on repairing individual gelcoat blisters and taking steps to prevent more gelcoat blisters in the future, read Repairing Individual Gelcoat Blisters in Epoxyworks Magazine.
Check out more Epoxyworks articles about using this epoxy additive to further enhance moisture exclusion: Retired Gougeon Technical Advisor Bruce Neiderer uses 422 to help keep gelcoat blisters at bay on Triple Threat, his 1981 Pearson Flyer that’s still competing on the Great Lakes today. Barrier Coat Additive was also used in restoring an International 110 class sailboat. And in completely rebuilding a rudder.
This downloadable PDF provides a detailed explanation of Moisture Exclusion Effectiveness (MEE), the property that 422 enhances when added to WEST SYSTEM Epoxy.