transom repair question

[WillyC]

I have a 1976 20' sf that I'm currently rebuilding. I've removed the plywood core from the transom (from the inside) and started grinding/sanding the last thin layer of plywood from the transom. There appears to be a layer of fiberglass/mat bonded to the gelcoat. My question is how much of this fiberglass layer do I need to remove by sanding with the grinder. There are areas where this fiberglass layer was not bonded to the gelcoat and water was actually trapped in between. I sanded away the areas that were not bonded well and don't know if I need to completely remove this fiberglass layer or just sand the surface down for a good bond with the new epoxy. Also what grit sanding disks will give a good bond with the epoxy. I started with 24 grit and dont know if I should hit it with 36 or 50 grit next. Thanks -Will

[EBEACH]

Will,

I had kind of the same thing on my 20. Scared the hell out of me when water came out from within the glass mat. I'd make sure you get all the water out, but don't go too crazy. The outer layer of transom is only about 1/8 thick mat. I'm working on my 23 right now and it is very thin.

[FELLOW-SHIP]

When I did my transom I didn’t find any water but it did get thin after I finished removing the plywood and cleaning it up. I built it up to over ¼” thick before I added any new plywood. If I were going to use the new composites material I would go up to 3/8” thick. When I go to boat shows and look at the transom blocks that most boat builders show the public their outer skin is approx 3/8” thick and the inner skin is approx ¼” thick.
FellowShip [img]/images/graemlins/wink.gif[/img]