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Project Difficulty:
Moderate
Estimated
Project Time: Varies with size and drying time
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Tack cloth
Work gloves
#0000 steel wool
Clean, soft cloths
For applying shellac:
Shellac
Denatured alcohol
Pure bristle brush
280- to 320-grit stearated sandpaper
Paste wax, as needed
Lamb's-wool pad, as needed
For applying varnish and polyurethane finishes:
Varnish
China bristle brush
Paint strainer or cheesecloth
Separate clean container
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Hand-held light
Jar
Paint thinner, as necessary
220-grit or finer sandpaper
600-grit wet-or-dry sandpaper
Mineral spirits
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In furniture restoration, "finish" refers to the material that coats the wood for the purpose of protecting and beautifying it. Although a finish can be tinited or colored, usually it's clear or almost clear. Except for painted finishes, the wood is usually colored using wood stains, wood fillers, or bleaching prior to applying the finish. In furniture restoration, shellac, varnish, and polyurethane are some of the finishes that are commonly used. Here's how to apply these three finishes.
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1.
Applying Shellac
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Shellac is a fast-drying natural resin that is not quite as water-resistant as varnish or lacquer. Always purchase fresh shellac for best results.
Shellac straight out of the can will be too thick to brush, will not flow well, and will dry too quickly. If you want to brush it on, thin the shellac about 50/50 with denatured alcohol; refer to package instructions for specific recommendations for mixing formulas. The more you thin the shellac the easier it will be to brush out, but the thinner each coat will become and the more coats you will have to apply. You can apply three to four coats of shellac a day, if the weather is warm and dry. Like all finishes, shellac dries slower in cool, damp conditions.
To apply shellac, follow the steps below.
1) Prepare and stain the surface as necessary. Use a tack cloth to remove all traces of dust from the surface. Work in a well-ventilated area.
2) Because shellac dries faster than varnish, you will have to use a special brushing method. Brush on the finish in the same direction as the wood grain, moving quickly so that each new brush stroke will overlap the previous one while it is still wet. If the previous stroke has begun to harden, your brush will drag, creating ridges that will cure in the finish.
3) Allow the finish to dry (about 30 minutes to 1 hour) and then, using 280- to 320-grit stearated sandpaper, scuff-sand the surface, being careful not to sand into and remove the stain (Fig. 1). Wipe surface with a tack cloth to remove all traces of dust.
4) Repeat Steps 2 and 3, applying as many coats as necessary (usually 3 to 4) to achieve the desired finish and allowing more drying time with each successive coat. Let the final coat dry overnight.
5) For a satin sheen, use #0000 steel wool to rub down the final coat (Fig. 2). For a semi-gloss to gloss sheen, wait one or two days for the finish to cure after the last coat, and apply paste wax with a #0000 steel-wool pad. Buff it with a soft cloth. For a gloss sheen, allow the wax to completely harden (about 1 hour), and polish the surface using a lamb's-wool pad.
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2.
Applying Varnish and Polyurethane Finishes
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Varnishes are produced by dissolving resinous products (synthetic alkyds, phenolics, or polyurethanes) in an oil. One of the most protective of all clear wood finishes, varnishes are available in several different sheens from gloss to flat. They are relatively slow-drying and the finish "film-builds," meaning it builds layer by layer.
To apply varnish, follow these steps:
1) Prepare and stain surfaces before applying the finish. Work in a clean, well-ventilated, and dust-free area that is also free of drafts. Use a vacuum or a tack cloth to clean the surface; don't brush or blow the dust off the wood or it will simply remain in the air and then settle onto the wet surface, ruining the finish.
2) Using a clean china bristle brush, transfer some of the varnish to a separate container. By doing so, you will avoid contaminating what remains in the original can, should you not use all of it on the current project. If you can see dust or dirt particles in the varnish, gently strain it through a paint strainer or a piece of cheesecloth, trying not to produce bubbles.
3) Position the surface to be finished as horizontal as possible. So that dust doesn't fall from your arm onto the newly applied varnish, begin at the far edge of your work and brush from left to right , gradually moving toward yourself. Brush the finish onto the wood, brushing in the direction of the wood grain and using a process called "tipping off" to smooth out your brush strokes. This will align your brush strokes with the wood grain, making them less noticeable. To tip off, hold the brush almost vertically, pulling and lifting it lightly in the direction of the stroke. (Fig. 3)
4) If possible, work with a hand-held light that can be reflected off the surface of the wood. A low-angle light will enable you to see runs, sags, and debris in the surface, allowing you to repair the finish before it dries. (Fig. 4)
5) To remove runs and sags that you see in the finish, drag your brush over the edge of a jar to remove excess varnish, and then lightly rebrush the flawed area.
6) When brushing varnish on, bubbles and brush marks will appear. They are unavoidable and are created by your brush. The trick is to get them to pop out before the varnish skins over and traps them. To lessen the amount of brush marks and air bubbles from curing in the finish, add a small amount of paint thinner to the varnish. The added thinner will extend the curing period, allowing the bubbles and marks more time to deflate and flatten out.
7) Allow the coat of varnish to dry (usually 24 hours), and then sand the surface using a 220- or finer grit of sandpaper. Wipe the surface with a tack cloth to remove all traces of dust.
8) Repeats Steps 3 through 7, applying as many coats (2 to 4) as necessary to achieve the desired look and letting the last coat dry 72 hours. Sand the last coat with a 600-grit wet-or-dry sandpaper and water or mineral spirits as a lubricant.
9) To produce an even sheen, rub the surface with #0000 steel wool, working in the direction of the grain. Wipe down with a clean, soft cloth.
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3.
Wiping Varnish
You can thin varnish with paint thinner and still use it as a finish. When varnish is half thinned, it is easier to wipe it onto wood and is called "wiping varnish." (Many manufacturers refer to their wiping varnishes as "tung oil;" read the label carefully to be sure of what you're getting.)
Apply wiping varnish just like full-strength varnish by brushing it on the wood and leaving it to cure. You can also apply it like an oil finish: Wipe it onto the wood, and then wipe off any excess. Wiping varnish cures faster than oil, so you have to work quickly. If you desire, you can leave a little of the varnish on the wood to achieve a thicker film-build for more protection.
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