Builders' Forum Archives
waterproof or vapor proof
Posted by LeeG on Sep 21, 2007
This is kind of confusing because you'd think something that is waterproof shouldn't allow ANY water to get into the wood. Except water,,and water vapor aren't the same thing.
The Okoume is great stuff, flexible, light, absorbant to epoxy with waterproof glue. Which means it absorbs water just great and given it's organic nature it's a great growing medium unlike other woods or dark colored woods that don't show mold/mildew as readily.
To protect the light colored pretty soft wood from water VAPOR requires multiple coats of epoxy. When one applies a thick sealing coat there are still places where small bubbles can develop or tiny channels of air to the surface can occur on dust particles.
I had another s&g kayak that had three thin fill coats under the deck but used float bags instead of closed compartments. Absolutely no problem with deck staining until I moved to a hot humid climate and left the float bags in the kayak. Moisture was trapped between the plastic float bag and the epoxy covered 4mm okoume deck. By the end of the summer dark mold areas corresponding to where the float bags sat starting showing through but NOT where the water was puddling on the underside the deck.
Water vapor makes its way through the epoxy in a way that standing water doesn't. Not that standing water won't find cracks in epoxy (which is why hull bottom panels need glass) but that water vapor goes through tiny cracks and thin epoxy that liquid water won't.
In Response to: Re: b) one coat of epoxy by Chris J. on Sep 21, 2007