Can Oil-Based Stain Bond Over the Varnish?

How Oil-based Wood Stains Work

• Oil-based wood stains are made from a combination of pigments, oils and solvents that can penetrate into the types of softwoods and hardwoods used in flooring, cabinetry, furnishings and toys. A stain manufacturer's instructions always direct users to apply their stains to bare wood. Here's why: Varnish, paint and polyurethane finishes are barrier coatings created for the purpose of blocking liquid penetration.

How Wood Varnish Works

• An oil-based varnish contains a mix of resins and solvents that keep the coating liquid until application. Once it comes in contact with stained wood, the varnish forms a thin polymer film that adheres to the surface. This film works as a sealant that keeps normal exposure to household dirt and spills from penetrating into the wood.

How New Stain Affects Varnish

• If the oil-based stain contains a solvent that is compatible with the existing varnish, it will partially dissolve the varnish and allow uneven penetration to the wood and uneven pigmentation of the varnish, creating splotchy coloration and uneven gloss. On the other hand, an oil-based stain may not have any effect on a chemical-resistant water-based polyurethane or epoxy-based varnish.

Strip, Stain and Varnish

• For optimal results, it is best to chemically strip off the old finish using an NMP-based paint and varnish remover before applying an oil-based stain. The NMP will soften the varnish and allow you to gently scrape it off with a plastic putty knife. Neutralize the stripper before applying the new stain, and then apply two coats of varnish as a protective finish.

Going for Grunge

• Not everyone favors a traditional finish for wood flooring and furnishings. Applying an oil-based stain over an oil-based varnish can help create a distressed or faux-industrial look. You can create a splotchy finish that resembles an old warehouse floor by rubbing the stain into an oil-based varnish with a lint-free cotton rag. This is likely to soften the varnish and create an uneven, mottled sheen. Once the varnish has dried again, apply two additional coats of matte varnish as a protective topcoat.