West System 422 Barrier Coat Additive

West System 422 Barrier Coat Additive is a blend you stir into mixed 105 epoxy to push its moisture exclusion further. Epoxy is already a good water barrier; 422 is for barrier coats on polyester fiberglass hulls, where the job is keeping water out of the laminate and helping prevent gelcoat blisters. It also makes the coat more abrasion resistant.

How much to add

Add 15 to 20% by volume, about 3 tablespoons per 8 fl oz of mixed epoxy. One 16 oz can modifies about half a gallon of mixed epoxy, so plan one can for every half gallon of barrier coat you will roll. It cures light gray. For coat counts and when to put bottom paint on, see our guide to an epoxy barrier coat below the waterline.

• Proprietary aluminum and mica blend, dry powder
• 422-16: 16 oz (453 g) can
• Cures light gray
• Improves moisture exclusion and abrasion resistance
• For West System 105 resin with any 200-series hardener

West lists it for fiberglass repairs, gelcoat blister repairs, boat restoration and rudder restoration. For a harder coat with limited UV protection, see 420 Aluminum Powder.