Smooth the surface with 220-grit sandpaper. Remove any rough edges to create an even, paintable surface.
Wipe away dust from sanding with a lint-free cloth. A lint-free cloth is a specialized type of cloth that allows you to wipe down a surface thoroughly without leaving any cloth fibers on the surface.
Stir the polyurethane with a stir stick. Stir slowly to avoid creating air bubbles.
Dip the tip of the foam paintbrush into the polyurethane and wipe away excess liquid on the side of the can. Dip the tip one additional time so the foam can absorb the liquid, and wipe away excess liquid on the side of the can.
Lightly brush on a coating of polyurethane. Brush the clearcoat onto the surface in one consistent direction. If you are applying a clearcoat to wood, brush the polyurethane in the direction of the grain. Allow polyurethane to dry for four to six hours before applying a second coat. Allow the finished product to dry for 24 hours.