How to seal WBP plywood

[slawosz]

Hi,
I need to strengthen soft core for my deck fittings. As boat is on mooring currently (limited work possibility), I will put plywood on top and bottom. I will use WBP as its easily sourced, cheap and read here its not big deal to I need to protect plywood from water. I am thinking about using West System as its quick and easy to apply. I heard opinions that sealing plywood completely is not the best idea (it needs to breath?). Is it true?

 

[rogerthebodger]

I use penetrating epoxy to both seal and strengthen soft plywood.

 

[fisherman]

have you considered using HDPE? It won't glue to anything, or bond with GRP, but it's tough, and readily available. In some cases a kitchen cutting board will do, I used it in place of an expensive piece of nylotron for years.

 

[Motor_Sailor]

WPB plywood only tells you that the glue is waterproof.
But you can get WPB made of soft wood or non durable tropical woods that will rot quickly.
In particular, 'fir-faced' ply will check and split even if painted really well with conventional paints.

Plywood that has been stored indoors and is still as dry (12%) as when manufactured, does not need to 'breath'. There are thousands of ply/epoxy boats built that are completely encapsulated.
But total encapsulation is the key - that means enough coats to form an effective barrier, including all the sharp edges and bolt holes, etc.

Much more satisfactory for backing up and reinforcing load bearing fittings is to make up (or buy) some flat, GRP 'plate'. Every boat owner should have a good supply: Get a large sheet of glass (old double glazing unit) or formica worktop. Give it a very good polish, and then layup alternative layers of glass matt and cloth until you get the 6 / 8 / or 10 mm you want. Use cheap polyester resin and you should be able to make a ready supply in half a day. Then cut it with a jigsaw into the shape you want and it'll be as durable and waterproof as the rest of your boat.

For high load backing plates, it nether crushes like plywood or creeps like polypropylene.

 

[slawosz]

Hi,
thanks for advices.
I will definitely use pure GPR plate when repairing this piece over the winter. For now, I need to do some repairs fast - I will stick to plywood - I live in flat and preparing plate in my case need trip to my sailing club, organising work, etc...

One more question - I drilled some holes in plywood bulkhead. I don't want them to be source of rot. Should I seal them,
or I could easily wait until October/November with sealing? It is very unlikely that they could be exposed to any direct water ingress (they are inside).