For illustration I choose to make a formula to show the consistency better. Whether epoxy, polyester or vinylester all should be plenty strong for this application. Epoxy is considerably stronger than polyester resin, in a secondary bond, and is what I personally use. My mix for illustration consisted of chopped strand fibers, West System 406 Coloidal silica or Cabosil, some West 404 and polyester resin. The same mix can be made with epoxy. When I shot this I was not ready to lay it up so used the less expensive polyester resin.


I like making my own "recipe" because it gives me more control over consistency and how it fillets. Kitty hair is another product I sometimes use but it will not fillet as well as your own custom mix will. For catalyst in the illustration I used some red dyed MEK-P. I like dyed MEK-P so you know you have it thoroughly mixed.


Wear rubber gloves and apply a thin coat of the mix to both the hull and backing block, then slather a large amount onto the backing block and thread it onto the thru-hull about three threads. I then used vise grips to grip the flange to prevent it from spinning and went out side the boat and used my step wrench to tighten down the thru-hull and seat the backing block.


Note: Epoxy will yield a much stronger bond than polyester resin but even polyester should give you about 500 PSI adhesion. ABYC standards call for the seacock to support a 500 pound static load for 30 seconds at the inner most hard fitting or hose barb.