How To Waterproof Plywood For Boat. 100% solids, marine grade epoxy will. A good rule of thumb is to add as many coats of sealant as there are in the plywood.
A latex liquid is applied on plywood and when it dries a plastic protective layer is formed. Acx exterior rated plywood is an affordable weather proof building material.
18mm Far Eastern Marine Grade Plywood 2440mm X 1220mm 8
After the the third and final coat, allow the boat to sit untouched for five to six days. Allow it to dry for three hours more and then apply a third coat.