Fiberglassing Over Plywood

[jimmoser]

The anchor hatch cover on my Catalina 30 is fiberglass over plywood. The plywood had begun separating from the fiberglass so I've pulled it off and sanded it down. So I think I'm ready to glass in a new piece of plywood.

Some questions:

1. Since the fabric will be on the inside of the locker, I'm thinking the fabric can be pretty light, 6 oz. right?

2. Because of the design, the plywood can't fully cover the underside of the hatch. (This explains why it separated. Weight on the hatch cover pushed the wood down onto the glass.) So my first thought was to increase as much as possible the plywood's coverage area. But it occurs to me that this leaves less area for the glass that will be holding it in place. Suggestions?

3. Anything I'm missing?

[mitiempo]

Is this plywood underneath a fiberglass hatch for stiffening? If so:

Use thickened epoxy to attach the plywood to the hatch. The mating surface of the plywood should be coated with straight epoxy first. The edges of the plywood should be rounded where the cloth will as the cloth will not adhere to a sharp bend.
Polyester is not as good at bonding or flexing as epoxy.

[jimmoser]

Thanks. Yes, the plywood is under the glass for stiffening.

[GaryHLucas]

The plywood failed, so you want to replace it with plywood? Why not replace it with fiberglass? Use a foam core of the same thickness as the plywood and glass over it. Or use some short pieces of PVC pipe as rib formers and glass over them. If it weren't for plywood in fiberglass boats a lot of them would have lasted a whole lot longer!

Gary H. Lucas

[jimmoser]

Hatch cover location makes it likely to get stepped on. Would balsa be strong enough?

[mitiempo]

Balsa or foam in this situation would require much better glass work. If the plywood is epoxied to the underside of the hatch and sealed with epoxy on all exposed surfaces as well and covered with the op's choice of glass cloth and epoxy it should last many years and is the easiest solution.

[SloopJonB]

Originally Posted by jimmoser

Hatch cover location makes it likely to get stepped on. Would balsa be strong enough?

Most decks are balsa core - I'd use foam core because it won't absorb water if the lamination gets breached in any way. If you buy the pre-scored foam it is much easier to fit than plywood because it can "droop" into the shape of the hatch. Set it in thickened epoxy and glass over the underside with a suitable number of layers of glass. It will be better than new.

[SlowButSteady]

I would put an initial coat of thinned (i.e., penetrating) epoxy to seal all the surfaces of the plywood, and then use thickened epoxy to bond the plywood to the fiberglass. The thinned epoxy will essentially be integrated into the first ply of the plywood, making it virtually impossible for separation to take place (barring delamination within the plywood, that is).