DIY Network

Wood Finishes: Clear-Coat Treatments From "Wood Works" episode WWK-504

In this segment, woodworking expert and Wood Works host David Marks talks about clear-coat treatments for wood.

Safety Alert: Always wear protective gloves, and ensure adequate ventilation, when working with wood stains, solvents and other toxic solutions.

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	Figure A
	Figure B
	Figure C
	Figure D
	Figure E
	Figure F
	Figure G
	Figure H
	Figure I
	Figure J
	Figure K
	Figure L

Varieties of Clear-Coat Treatments

Finishing coats include oils, varnishes, urethanes, shellacs, and lacquers. These are the transparent coatings that seal in the color as well as protect the wood.

There are two main types of finish coats:

• Air-oxidizing finish coats include the oils (e.g., tung oil and linseed oil), varnishes, urethanes (e.g., polyurethane) and blends. These finishes penetrate the surface of the wood.

• Solvent-releasing finish coats include lacquers and shellacs. These leave a hard, transparent coating of resin on top of the wood. Transparent coating treatments are made of tough resins that are dissolved in solvents and built up on the wood in layers. The first layer is the sealer coat. It locks down the fibers and fills in the pores of the wood. All subsequent coats are considered topcoats. The additional coats add color, protection and sheen.

Application Techniques: Oil Finishes

• Air-oxidizing oil-treatments like tung oil are easily applied to the surface of raw or colored wood, and leave a natural look and feel (figure A). Oils, however, offer little moisture- or wear-resistance, and they may yellow over time.

• Tung oil comes from the seed kernel of the tung tree which originated in East Asia. Hand-rubbed tung-oil finish is one of the most beautiful and versatile of wood finishes.

• Linseed oil is another woodworker's favorite, and it has been used for thousands of years. Pure linseed oil takes a long time to dry, so most commercial types are boiled to reduce drying time. Apply liberal amounts of the oil (figure B). Once it has had a chance to soak into the wood, wipe away the excess with a lint-free rag. Then let the finish dry overnight at a temperature of 70 degrees or warmer.

• After the first coat has dried, burnish the surface using "0000" steel wool (figure C). Clean away any dust, then apply additional coats in the same way -- burnishing the finish between coats -- until you have 4 to 5 layers built up.

Application Techniques: Lacquers and Shellacs

• When dry, shellacs and lacquers leave a hard glossy film on the surface of the wood. Shellac is a non-toxic resin that's a natural gum secreted by the lac bug of southern Asia. Gum or resin flakes (figure D) are dissolved in denature alcohol to prepare the brush-on finish solution. Once the finish is applied, the alcohol evaporates leaving the shiny coat.

• Shellac's clarity, depth and shine make it a traditional favorite among woodworkers. The color of the finish may vary from light brown to dark brown (figure E).

• Lacquers, such as the one used on the wood urns turned by David Marks (figure F), provide a shiny, protective finish that is also water-resistant. Lacquers dry quickly, have great clarity and build well through layered application. The vessels shown in the demonstration were finished with 15 to 20 coats of lacquer to create a glass-like shine.

• "Lacquer," says David Marks "is definitely the Rolls-Royce of finishes." For instance, lacquers are used to create impressive finishes on hand-crafted guitars like those made by Tom Ribbecke, one of the world's top makers of arched-top guitars (figures G and H). Tom's work has been shown at the Smithsonian, and is marked by a mirror-like finish and a three-dimensional effect achieved by coloring the lacquer.

• Before applying lacquer, it's a good idea to pour it through a filter to remove solid particles (figure I).

• Lacquers are formulated to dry fast, so they should be sprayed on. To get a feel for spraying on lacquer, practice spraying onto a sheet of cardboard (figure J). Set the fan pattern to best cover the work area with little over-spray.

• Safety Alert: Since lacquers have a high solvent content, be sure to work in a well-ventilated area, and wear a charcoal respirator.

• Once you're ready to apply the lacquer, hold the sprayer 6 to 10 inches from the surface, and spray the least accessible areas first (figure K).

• Move your arm and wrist at a uniform rate as you spray, and try to begin and finish each stroke several inches past the edge of the project. Give the first-pass coating a few minutes to flash off, then make a second pass using spray strokes that are perpendicular to those done for the first pass (figure L).

• Once the first coating -- the sealer coat -- dries, sand it with 320 open-coat sandpaper and then remove the dust. Repeat the steps to apply additional coats. The more coats you apply, the more depth you'll build in the resin coating.
  

In the segment that follows David Marks discusses methods for finalizing wood finishes.