We choose plywood because it is cheap, easy to work with and generally plentiful in supply.
However, unless you pay a good deal more you have to appreciate that our material of choice is not perfect. To use it in boat building, even on our scale, it must be treated before you get very far into the job.
Gary recommends penetrating epoxy which is obviously the best choice, he should, and does know such things. However, depending on where you live and what is available you may not be able to get this in smaller quantities, if at all.
So, what to do? My Irene was treated with 1:4 Boncrete/water as this product is used not only for bonding timber but also in mortar and grouts as water proofing./bonding agent. It is certainly cheap enough. Currently I’m testing conrete Sealer which is solvent based, not water, and to date it seems a cheap and effective sealer for plywood.
But what is it about ply that makes it so imperative to waterproof it? Ply is, in this build, 3mm approx. 3 ply. The adhesive used is sufficient to hold the ply together for cutting, shaping and fixing but as you will soon find, depending on the grade of ply, it is not hard to separate the top ply if care is not taken. But the main concern is stopping water, even moisture, from entering the ply and weakening the adhesive as the timber swells.
So far, in my own three boat experience, the main damage is likely to arise if the edges of the ply are not totally sealed. And this means ALL edges, in glue or otherwise. One of my deck structures inadvertently went unsealed on the edge sitting on the deck (and that is not normally where it would be) and although seemingly bedded in epoxy, water from deck wash found its way in and it was evident when the enamel painted surface showed up alarming ripples. If you are using door skin as a featured deck material it will need to be well sealed even so with clear enamel or synthetic varnish/sealer. If you don’t, it wont take a lot of U.V. to let moisture through and ruin the deck.
All this is just my 2 cents worth, can anyone add to it for the benefit of those just starting a build?
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