I just picked up some of the water base urethane today to use as a last resort. I have used other colors of the Rusty on other planes and never had a problem. I am now thinking that my test might not have been valid. I had sprayed a sample of each color on ceramic saucers since this was handy. This may retard the curing process since it is not porous as is wood or covering material (Coverite). So I have decided to test again on wood before I resort to the added step of clear coating.