I am making a couple outdoor signs for a friends dog boarding business. My first try at it. 1 sign will be the business logo and the other the word Welcome. Both are cut out of mdo plywood, have been primed and painted, both water based. The backing is mdo plywood with cedar fence pickets glued and brad nailed to it. I used 2 applications of Thompsons waterseal on the cedar. I am putting Varathane Spar Urethane on the painted parts before assembling the signs. My question is, what would happen if i put the spar urethane on that watersealed cedar? Im guessing it wouldn't adhere to it very good. Being my first time making the sign, i didn't think thinks through very well so everything worked good together. Thanks