Wipe-on application

Overview

Wiping varnish is a brushing varnish thinned to a wipeable consistency, often with a little oil added. Bob Flexner calls it possibly the most popular hand-applied finish: as easy to apply as an oil, but far more moisture, scratch, heat and solvent resistant. You can make it yourself by thinning any oil-based alkyd or polyurethane varnish about half with mineral spirits, or buy it ready-made under a confusing range of names. Because each coat is very thin, the technique is forgiving: runs, brush marks and bubbles mostly cannot form, and dust nibs are sanded out between coats.

When to use

• You have no spray gear and want more protection than Boiled and raw linseed oil or Danish oil give.
• Tabletops, chairs, cabinets and anything handled daily; see Tabletop finish schedules.
• Not for outdoor work or for water-based finishes, which wipe differently (see Brush application). Wipe-on products labelled interior only stay indoors; see Outdoor finishing.

Materials and tools

• A wiping varnish (Wipe-on polyurethane, Oil-based polyurethane thinned, or an oil-varnish blend), plus mineral spirits for thinning and wet-sanding.
• Soft, lint-free cotton cloth folded into a pad. Fold the cloth back on itself and pinch it closed for a smooth, slightly convex face that leaves no track marks (Woodcraft).
• A 2 in natural-bristle brush if you use the faster method. Flexner prefers natural over synthetic and warns that cheap chip brushes shed and foam brushes soak up too much finish.
• 320 or 400 grit paper; a raking light.

Steps

1. Sand to at least 320 (Fine Woodworking) or through 220 for a first-coat sealer approach (Woodcraft; General Finishes' data sheet says raw wood no finer than 220). Remove dust; see Dust removal and tack cloths. Work at 65 to 80F.
2. Coat 1, thin: if the product is thick, thin it about 50% with mineral spirits (up to 100% for very thick varnishes, per Woodcraft). Flood it on, re-wet dry-looking spots, and wipe off all the excess after about 10 minutes, or when it just turns tacky. Dry overnight.
3. Coat 2: wipe on heavier with circular strokes, then level gently along the grain without wiping it off. Fine Woodworking dries it overnight.
4. Level: wet-sand with 400 grit lubricated with mineral spirits to remove nibs and hardened bubbles (a third thin coat wet-sanded works too). Wipe off the slurry.
5. Add thin coats. Flexner's faster method: brush or wipe it on, then drag an almost-dry brush over it, wiping the brush on a clean cloth after each stroke, and finish with light strokes with the grain. This builds faster than wiping off and works on vertical surfaces.
6. Between coats sand lightly with 320 to 400 by hand once dry (overnight for Flexner; Minwax says 2 to 3 h, then 220 grit). Stop after four to six coats for a thin film; build higher for more protection, then rub out; see Rubbing out a finish and Build coats and sanding between.

Common problems

• Sticky or soft film: too much oil in the blend, or coats left thick. Wiping varnish should resist a fingernail after a day or two on glass (Woodcraft test). See Troubleshooting finish defects.
• Streaks and tracks: pad too dry or dragged; re-wet and level, or wet-sand the next coat.
• Runs on vertical surfaces: straight brush-and-leave is only for flat tops (Flexner); use the brush-off method elsewhere.
• Lint: use clean cotton, not paper towels.

Safety and environment

Oily rags can self-heat and ignite. Minwax says rags may spontaneously ignite and should be kept in a sealed, water-filled metal container; Woodcraft says hang or spread them flat. See Oily rag safety. Ventilate and avoid solvent fumes.

Related

• Wipe-on polyurethane, Oil-based polyurethane: the usual wipe-on products.
• Thinning and viscosity: how much to thin.
• Brush application: for thicker builds.
• Curing conditions and time-to-use: why damp or cold rooms stall drying.