THE OWNER BUILT HOME & HOMESTEAD
(Page 10 of 13)
September/October 1972
By Ken Kern
Polyurethane-based, phenolic gum and phenolic tung oil are the best commercially available natural finishes, though they last only two years at the longest. An eight-year natural finish was developed some years ago by the Forest Products Laboratory, which publishes this formula for a 5-gallon batch, cedar color:
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Pour the gallon of mineral spirits into a 5-gal., open-top can. Put paraffin and zinc stearate in another pan and heat over flame, stirring until uniform mixture results. Pour this into the mineral spirits, stirring vigorously. Keep flame away from mineral spirits. When solution has cooled to room temperature, add pentachlorophenol concentrate, then linseed. Stir in colors until mixture is uniform, and it's ready for use. For redwood color, use 1/2 pt. burnt sienna and 1/2 pt. raw umber, plus 1 pt. pure red oxide color-in-oil.
Shingle stains can be used also on rough-sawn siding. Linseed or oil-modified alkyd coatings are the best here, as a porous paint film is necessary to allow moisture to escape and thereby prevent blistering. Regular shingle stain is composed of a color dissolved in oil-containing solvents and a wood preservative such as creosote. Preservation of the shingle depends upon adequate penetration of the stain rather than the formation of a protective outside film, while with regular paint, on the contrary, adhesion of the film to the surface is more important than penetration.
It has been found that 90% of all paint failures are due to the poor lumber used as the base—mainly the high moisture content of the wood, or moisture entering the back side of the wood after it has been painted—through condensation due to faulty gutter and flashing. Blistering is a common result of moisture destroying the paint bond. Paint will adhere best to slow-grown spring wood and will tend to peel from fast-grown summer wood. Paint will also last longer upon narrow-band, edge-grain boards than upon wide-band, flat-grain boards.
Alligatoring, the final stage of checking, is one common paint-mixture deficiency. It results from having too much oil in the prime coat. The prime coat should always be harder than the final coat. For this reason it is important to allow plenty of time between coats, as exposure to the air causes a hardening action (oxidation) to take place. The final coat should be elastic enough to respond to the expansion and contraction of weather change.
Lacquer, shellac, spar varnish, linseed, or alkyd can all be used on interior wood paneling and plywood. Alkyd is an excellent sealer for plywood. Alkyd gloss or semi-gloss paint will last as long and retain color as well as any paint now sold. If a colored surface is desired, one of the styrene-butadiene, polyvinyl acetate, or acrylic latex paints is an excellent choice. Already, the greatest volume of water-emulsion paint sold in the United States is of the latex type. Such paints dry rapidly, are easily applied, have no odor, have good scrub resistance (after hardening), excellent penetration, and good color-uniformity.
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