Varnish Care

This transparent finish highlights everything from the wooden bow of a classic runabout to teak trim on production boats. To keep that glossy finish, it's important to carefully tend to your wood's surface.

Because varnishes have a transparent finish, they don't have the durability of pigmented finishes. While the sun's rays reflect off the top of a pigmented paint or other wood treatment, they penetrate a clear varnish and then reflect back up again. Consequently, a varnished wood's surface feels the wrath of the sun's rays much more than a painted wood surface. For that reason, you'll need to apply many more coats of varnish than would be required with paint, and you should consider using one that has UV protection.

Never apply less than two coats, even when giving a refresher treatment to brightwork. Sanding the old varnish or bare wood surface before application of the varnish finishing system is critical. Use 180–220 grit sandpaper. While sanding, consider wearing goggles and an OSHA approved breathing mask to protect from dust.

Don't use steel wool. It does more polishing than cutting and leaves fine steel wool particles in the pores which may rust and prevent good adhesion of subsequent coats.

Between coats of varnish, the grit size of the sandpaper should be reduced to 220–320 in order to eliminate sandpaper scratches in the finish film.

Don't wash or wipe a fresh varnish coat with solvent or thinner. It may lift the varnish. It's also bad practice to wipe any sanded surface with thinner or solvent, since it penetrates into the pores and prevents good adhesion on subsequent coats. The best method to remove sanding dust is to wipe the surface with a denatured alcohol to ensure the surface is free of contaminants and follow up with a tack cloth just before applying varnish.

Mahogany is an open-grained wood that requires a quality filler stain on the bare wood to produce a smooth, glass-like appearance when varnished.

Teak can be varnished satisfactorily, although it has a naturally high resin content that sometimes bleeds to the surface and can prevent good varnish adhesion. Your results may vary depending on the character of the teak involved, how weathered it is, and other factors. A suggested technique is to sand the teak surface thoroughly, wipe down with a denatured alcohol, let dry, and apply a coat of 50% thinned varnish. Let the varnish dry thoroughly before application of subsequent coats.

Varnish Tips

• Apply varnish by brush, roller, or spray, six coats minimum on new wood, two coat minimum over old varnish.

• Wear a mask to avoid inhaling fumes.

• Sand between coats with 220–320 grit sandpaper.

• Don't shake or stir a varnish. It creates bubbles and froth.

• Pour varnish through a paper strainer into another clean container for use, then tightly close the varnish can.

• Store varnish can upside down to ensure a good seal.

• When applying oil-based varnishes, use a tack rag to remove static dust for the cleanest possible surface just before applying varnish. Apply in as dust free area as possible.

• Use a good brush and be sure the brush is clean. This can't be overstressed.

• A high-quality natural bristle brush should be used when applying oil-based varnishes and a high-quality nylon, nylon/polyester, or foam brush should be used for water-based polyurethane varnish application. Foam brushes are also practical for small jobs. Use a comb to remove dust and bits of varnish from the bristles before dipping the brush into the varnish.

• If the bubbles are forming in the varnish during application, many times they can be eliminated by changing the type of brush being used.

• Always brush into the wet edge. That is, don't start a fresh brush out of varnish from the previous brush load, but rather brush into the previous brush load. That will eliminate brush marks and overlaps.

• Avoid applying varnish in direct sunlight, or late in the day if night time dew is expected.

• When brushing varnish, thin 0-5% if the varnish becomes too thick.

• When brushing varnish, thin 0-5% if the varnish becomes too thick.

• Never apply varnish to the bottom of a wooden boat, except for those that are day sailed. Prolonged immersion will lead to blistering of the varnish film.

• Test the finish on a spare piece of wood before applying to the boat.

• Always follow product instructions.

Doug Theobalds of Epifanes contributed to this article.