How do I make my custom coasters waterproof?

Waterproofing a coaster is about building up a sealed barrier in thin, even layers rather than one thick coat.

• Apply 2 to 3 thin coats of clear polyurethane spray or brush-on acrylic sealer.
• Let each coat dry fully before adding the next so it cures hard.
• For wood coasters that see heavy use, step up to marine-grade polyurethane.
• For a glass-like, fully sealed top, pour a thin layer of epoxy resin over the surface.

Water should bead on the finished surface. If it soaks in, add another coat.