How to Waterproof Over Shellac

Shellac is an all-natural sealer and finish that's nontoxic, dries quickly and can be combined with most other finishes and used as a first coat or sealer for your wood project. While shellac is versatile, it's not completely waterproof. If you want the final finish on your woodwork to be fairly weatherproof, you will need to add another type of finish on top of the shellac.

Use a fine-grit sandpaper to remove any burrs and to smooth your shellac finish. Hand sand the surface gently with 1/4 sheet of the sandpaper folded into fourths, taking care to sand only with the grain of the wood.

Wipe the sanded surface down with a clean damp rag to remove all dust. Allow the surface to dry.

Select a can of waterproof polyurethane or oil wood finish. Open the can and mix it thoroughly with a fresh stirring stick. Take care to scrape the bottom of the can and to stir the finish slowly using a figure eight motion until the mixture is uniform.

Set your piece of shellacked and sanded wood on blocks, arranged 1 or 2 inches from the sides of the piece. Keep a sponge and a jar of paint thinner handy so you can quickly clean up any drips.

Dip the bottom third of the paintbrush into the finish and apply a thin, even coat to the wood surface. Take care to brush the finish on with the direction of the wood grain, not against it. Wipe all sides and the underside of the piece with a sponge and paint thinner.

Repeat these steps, allowing the wood to dry between each coat. Apply one to three coats of finish -- more finish will increase the final piece's shine and the durability of the finish. Do not sand after the final coat.