A buddy of mine restores Super Cubs, he uses Stewart Systems except for the paint.For paint he uses Martin/Senior Prism Urethane,his personal 2 Cubs have had it on for over ten years and it still looks great. The way he explained it to me is the water is just a carrier and you can put Urethane over it without any problems.I put some of Stewarts filler on a sample piece of fabric and even sprayed carb cleaner on it and it wouldnt touch it. Super good stuff.