Installation, care, and maintenance of wood shake and shingle siding instructs us in the proper finish to apply to cedar siding. Wide selections of oil- and latex-based finishes are available for shakes and shingles. Oil-based finishes are solvent-borne, and latex-based are water-borne; however, in recent years the solvent-borne finishes often have co-solvents in them to make them water soluble. As with any other wood product, shakes and shingles can be finished with water-repellent preservatives (WRP) (clear and lightly pigmented), semitransparent stains, solid-color stains, or paints.
Water-repellant preservative is a generic term that describes a clear penetrating finish that traditionally was formulated with about 10% to 20% oil or alkyd binder, 1% to 3% wax or similar water repellent, a preservative, and an organic solvent such as mineral spirits or turpentine. The finish does not contain a pigment and gives a natural wood appearance.
The low wax content in some of the traditional WRP formulations made it possible to use them for pretreatment of wood prior to painting. They were also an excellent pretreatment for shakes and shingles prior to installation. Bundles of shingles could be dipped. Most of the finish was absorbed into the end grain at the butt end of the shake or shingle and gave years of protection by minimizing end-grain water penetration.
To meet stringent air quality requirements, these solvent-borne types of WRPs are no longer available. They have been largely replaced by water-borne formulations and formulations having low organic solvents content. Many of these formulations are intended for use on wood decks, but they can also be used on siding. These finishes often are tinted with a small amount of pigments, UV stabilizers, and other additives to improve their service life.
They give some water repellency and inhibit mold and algae growth on the lateral surface. If used on single-story structures having wide roof overhang, they give about 2 to 3 years of service, depending on exposure.