How many layers of glass to make a strong joint?

[infx708]

I've got an 8' piece of plywood and a 2' piece to join together. Going to connect them with a small piece of plywood on the underside. Planning on glassing the whole thing. How many layers and what weight of cloth should I use to make it work? The joint is toward the stern, just forward of the splashwell, so there shouldn't be a lot of traffic or weight on it.

 

[Labman]

Re: How many layers of glass to make a strong joint?

I have to splice all my stringers, the shortest is 10', I plan on using a Biscuit Joiner, Gorilla glued and 1 coat of 1.5 oz. mat covered with 1 coat of 6 oz. cloth, the supplier figured that would be enough.

Oops! has a good detail in his project posting.

 

[Mark42]

Re: How many layers of glass to make a strong joint?

I think the way you want to join the plywood is fine. Just make sure the piece on the underside is at least 1 ft wide, giving 6" on each side of the joint. Use a water proof wood glue or construction adhesive. Use screws to draw the pieces together until the glue dries. Pre-drill the holes on the top piece so the screw just bites into the lower piece and pulls it up snug.

As far as the fiberglass, one or two layers of 6 oz should be fine. You are just trying to create a waterproof barrier on top of the ply, and the mat will just make a bumpy layer that will show through the 6 oz, and leave many air gaps or require lots of unecessary sanding to make it smooth. You are not trying to build up strength, just make a protective barrier. The 6oz will lay nice and smooth over the ply.