Shellac is a classic finish for premodern woodwork, and it therefore remains a major finishing choice for those engaged in authentic restorations and re-creations of historic wood furnishings, implements and fixtures. The problem with shellac, and part of the reason why it has fallen out of fashion as a modern wood finish, is that when used alone it is easily damaged by water and alcohol. To produce a lasting shellac finish, a transparent sealant must be put on top.
Lay out a drop cloth or several layers of old newspapers, and put the wood object on top of that.
Sand the surface of the shellac finish lightly with fine-grit sandpaper on a hand sanding block. Sand the finish only as much as is necessary to scuff it up a bit with micro-scratches, creating a better surface for the waterproofing sealant to bond with. Do not attempt to remove the finish or any substantial amount of wood.
Wipe the wooden object down with a tack cloth, to remove dust and bits of sawdust and finish.
Apply a coat of transparent polyurethane to the wooden object, using long strokes with a paintbrush. Wait several hours (or as directed on the instructions) before applying a second coat.
Tips & Warnings
- Select your transparent polyurethane carefully, so it matches the shellac finish already in place. If the shellac has a flat finish, you don't want to use high gloss polyurethane, since this changes the look of the finish while waterproofing it and defeats the purpose of staying with a shellac finish in the first place.
- Do not use power tools to sand the wooden object, since they will remove far more finish and wood than is necessary to prepare the surface for waterproofing.
Things You'll Need:
- Dropcloth or old newspapers
- Hand sanding block with fine-grit sandpaper (180-grit or higher)
- Tack cloth
- Transparent polyurethane
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