A boat restorer friend of mine told me he uses 7 coats of spar-urethane on the mahogany boats that he restores. He says with the sanding between coats you need at least 7 coats to have a durable finish on boats. Being a woodworker myself I know moisture will be absorbed by wood, so all sides need the 7 coats so that moisture is absorbed evenly by the wood. Oak has a tendency to turn black with any moisture that gets to the bare wood. The cupping and cracking again was the result of moisture getting to the wood. If there is an area that the urethane did not fully protect moisture will find it! My bed is going on three years now and it still looks great.
