What Kind of Varnish Goes Over Painted Wood?

Choosing a Varnish

• A water-based urethane varnish, referred to as polyurethane, is what many consider to be the best clear coat for painted wood, as it offers excellent durability against scratching, denting and staining. It comes in spray and paint-on forms, in satin or glossy sheen. Spray is recommended for beginning and intermediate do-it-yourselfers because it’s less likely to bubble or drip. Oil-based varnish is less durable than polyurethane, and it initially can darken the paint and cause yellowing over time. A third type, spar varnish, is used primarily as a marine varnish.

Curing the Paint

• Although paint quickly dries to the touch, it can take several days before it loses all its moisture and fully hardens. This hardening process is called curing. The paint should be fully cured before you varnish it. Curing may take two or three days if you paint the wood with light, even coats. Give it a few extra days if you paint thicker coats.

Prepare the Surface

• If the cured paint has any sheen, sand it with fine, 100-grit sandpaper to remove the shine. Sanding smooths away imperfections and helps the varnish adhere better. After sanding, wipe the wood with a tack cloth. Tack cloth has a sticky surface that grabs the sawdust without reintroducing moisture to cured paint.

Achieving a Flawless Finish

• Varnish painted wood in a dust-free environment. Wipe it with a tack cloth before you begin, then wait a few minutes to allow dust to settle. Follow the manufacturer's recommendations for air temperature. The polyurethane won't spread or properly dry if temperatures are too warm or too cool. Apply spray-on polyurethane with light, sweeping strokes that slightly overlap. Follow the manufacturer's instructions for drying time. Dull the surface and smooth away imperfections with 220-grit sandpaper or steel wool between coats. Apply two to three coats. Polyurethane cures in approximately one week.