: I have epoxied some cardboard to see if it was possible to do a S&G kayak out
: of some quality boards (there must be different grades of cardboard) My
: problem was saturation of the inner segments of the board ... I just
: failed to develop confidence in the boards.

: But I still epoxy the outsides of cardboard boxes when I need a lasting,
: sturdy container. This may be better than watching epoxy cook off...

Kraft paper honeycomb used to be a popular way to make some relatively waterproof structures. Assuming the outside remains fully waterproof the internal cardboard structure would too. Would be bad though if the outer surface were damaged. I know phenolic coated cardboard is available, don't know from who though and that would work. Plywood is easier

Bill H.