Varnish is a clear or lightly tinted protective finish for wood and other materials that dries to a hard, transparent film, sealing out moisture, resisting wear and UV light, and enhancing natural grain; made from resins, oils, and either solvents or water, it’s commonly used on furniture, floors, trim, cabinets, doors, and outdoor pieces to improve appearance and durability.
What Is Varnish?
Varnish is a transparent or slightly tinted coating that forms a tough, protective film over wood and some other surfaces. It’s made by combining resins and oils with a carrier (either a solvent or water). Once applied, the carrier evaporates and the resins cure to create a durable layer that protects against moisture, abrasion, and, with some formulas, sunlight. Unlike paint, varnish is usually clear, allowing wood grain and color to show through and often look richer.
How Varnish Works
Varnish cures into a continuous film that blocks water and slows oxygen and UV damage. Oil-based formulas tend to add a warm, amber tone and build a slightly thicker film per coat. Water-based versions dry clear, stay clearer over time, and have lower odor. Many modern “polyurethanes” are technically varnishes that use polyurethane resin for added toughness.
Common Uses at Home
- Furniture: Tables, chairs, dressers, and built-ins.
- Trim and doors: Baseboards, window trim, and interior/exterior doors.
- Floors: Hardwood floor protection and sheen control.
- Kitchen and bath woodwork: Cabinets and vanities (choose moisture-resistant types).
- Outdoor projects: Benches, railings, and doors (use exterior/spar formulas with UV inhibitors).
Types of Varnish
- Oil-based varnish (alkyd/phenolic): Durable, warm amber tone, longer dry times, stronger odor. Good for furniture and trims where depth of color is desired.
- Water-based varnish (acrylic/polyurethane blends): Low odor, fast drying, clear to non-yellowing. Great for light woods like maple or birch and for indoor projects where quick recoating helps.
- Polyurethane (oil or water-based): A resin type known for abrasion resistance. Common for tabletops and floors.
- Spar or marine varnish: Formulated for exterior use with UV absorbers and added flexibility to handle temperature and humidity swings. Needs periodic maintenance outdoors.
- Wiping varnish: Regular varnish thinned for wipe-on application. Builds slower but is easier to control, especially on small parts or tricky shapes.
Related but different finishes:
- Shellac: Alcohol-based, warm tone, easy to repair, not as water-resistant.
- Lacquer: Fast-drying, spray-applied in most cases, used in shop settings.
- Oil finishes (tung/linseed blends, Danish oil): Penetrating finishes that don’t build a thick film; often topped with varnish for more protection.
Choosing the Right Varnish
- Location: Interior pieces do well with oil- or water-based polyurethane. Exterior pieces need spar/marine or exterior-rated polyurethane with UV inhibitors.
- Color and clarity: Oil-based adds amber warmth; water-based stays clear. On maple, birch, and white oak, water-based preserves a pale look. On walnut or cherry, oil-based can enhance depth.
- Sheen: Gloss, semi-gloss, satin, and matte. Higher gloss shows grain and imperfections more; satin/matte hide minor flaws and fingerprints.
- Dry time and odor: Water-based dries in 2–4 hours between coats; oil-based may need 8–24 hours. Consider ventilation and schedule.
- Traffic and wear: Tabletops and floors benefit from polyurethane resin for abrasion resistance.
- Compatibility: Water-based varnish can go over oil-based stains after the stain fully dries (often 24–72 hours). When in doubt, use a dewaxed shellac sealer as a barrier or do a test board.
How to Apply Varnish (Step by Step)
- Prep the surface: Sand wood through 120–150–180 grit for most projects. Vacuum and wipe with a damp rag or tack cloth to remove dust.
- Stir, don’t shake: Stir gently to avoid bubbles. Shaking traps air that causes foaming and craters.
- Thin if needed: Some products benefit from thinning 5–10% (check the label). Wiping varnish is already thinned.
- Control your environment: Aim for 60–80°F (15–27°C), moderate humidity, and low dust. Avoid direct sun and drafts.
- First coat: Brush with a high-quality natural-bristle brush for oil-based or a synthetic/nylon brush for water-based. Work with the grain and keep a wet edge. For wipe-on, apply a thin, even coat with a lint-free cloth.
- Dry and sand: Let the coat dry per instructions (2–4 hours for water-based, 8–24 for oil-based). Sand lightly with 220–320 grit to remove nibs and improve adhesion. Vacuum and wipe clean.
- Build coats: Apply 2–4 coats for furniture; 3–5 for tabletops and floors. The final coat sets the sheen.
- Cure time: “Dry to touch” isn’t fully cured. Avoid heavy use for several days. Full cure can take 7–30 days depending on product and conditions.
Application tips:
- Tip off brush strokes by lightly dragging the brush in the direction of the grain.
- For water-based varnish, lightly mist the floor or surrounding air to settle dust (avoid getting water on your work).
- For end grain, seal with a thin first coat to avoid dark spots and excessive absorption.
Maintenance and Care
- Clean with a soft cloth and mild soap solution; avoid harsh chemicals or ammonia-based cleaners on oil-based finishes.
- Use coasters and felt pads. Avoid hot pans directly on varnished surfaces.
- For sheen refresh, scuff with 320 grit and add a maintenance coat. Outdoor varnish may need annual light sanding and recoating before it peels.
- Avoid silicone polishes; they can cause adhesion issues later.
Safety:
- Ensure good ventilation, especially with oil-based products.
- Rags soaked with oil-based varnish can spontaneously combust. Lay them flat to dry outdoors and dispose of in a metal container with water and a tight lid per local guidelines.
Common Mistakes to Avoid
- Applying too thick a coat, leading to sags and slow curing.
- Skipping sanding between coats, which reduces adhesion and smoothness.
- Shaking the can, which introduces bubbles.
- Coating in high humidity or cold conditions, causing blush or extended dry times.
- Mixing incompatible products (e.g., applying water-based over oil that hasn’t fully dried).
- Not testing on scrap or a hidden area for color and compatibility.
Related Terms
- Polyurethane, spar urethane, acrylic, alkyd, phenolic resin
- Stain, sealer, shellac, lacquer, oil finish
- Sheen levels: gloss, semi-gloss, satin, matte
Practical Examples
- Pine dining table: Sand to 180 grit, apply an oil-based polyurethane for warmth and durability, three to four coats with light sanding between.
- Maple desk: Use a water-based polyurethane to keep the pale color. Apply three coats; final coat in satin for reduced glare.
- Exterior wooden door: Choose a spar varnish with UV inhibitors. Apply four to six thin coats, and plan on a light maintenance coat each year.
- Hardwood floors: Use a floor-rated polyurethane. Apply with a T-bar or pad applicator, allow full cure before moving furniture back.
With the right product and method, varnish adds beauty and long-lasting protection to new builds and refinishing projects alike.