I don't know, but after overbuilding a few kayaks, this time I didn't seal the under deck of my north bay well enough. after finishing with 6 coats of varnish I had left the hatches on the kayak for a few days.... hmm temp. in the high 90's and humidity too, dark patches appeared concident with the areas under the deck that weren't reinforced and just had the one thin initial sealing coat. sigh. I let it dry out then sealed it in the cool of the garage. other kayaks haven't done the same so I would guess two coats .