Natural Wood Finishes for Exteriors of Houses

There are two types of natural finishes: penetrating intrasurface coatings which soak into the wood, such as oil finishes, wood sealer finishes, and water-repellent preservative finishes; and surface coatings, such as varnish. The oldest of the penetrating finishes is linseed oil, either boiled (containing driers) or raw. These oils finishes impart very little gloss and darken the color of the wood more than other natural finishes. The addition of pigment usually adds to the durability of oil finishes, which serve best in dry areas such as southern Arizona where there is no long period of dampness and threat of mildew. Although most wood sealers are more resistant to mildew than oil finishes they are less resistant than good house paints. A water-repellent preservative is a solution of hydrocarbon wax, such as paraffin, resin, or resin and nonvolatile oil, and a preservative, such as a chlorinated phenol, in mineral spirits or other volatile solvents. Varnish finishes leave a coating of appreciable thickness on the wood; in time, darkening of the varnish itself will cause the original clear, glossy finish to darken. The best varnish for large areas is one that disintegrates by a very fine crazing followed by fine crumbling. The new synthetic-resin varnishes may remain free from crazing and maintain gloss for a relatively long time, but in the end they tend to crack, curl, and scale badly.

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