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Cedar accepts many types of finishes
The choice of an exterior wood finish for cedar depends upon the desired
appearance and the degree of protection required. Conversely, the amount of
protection provided to the wood depends on the type of finish selected. Finished
wood is a combination of two widely different materials and the properties of
both must be considered to achieve the most durable wood-finish system. Note,
however, that with all types of finishes, the manufacturer's recommendations
should be followed. Cedar's excellent finishing characteristics cannot
compensate for products that are unsuitable, of inferior quality, or improperly
applied. Finishes perform best when the coating is applied to all surfaces
(face, back, edges and ends).
In general, finishes for cedar can be grouped into four categories: (1)
opaque coatings, such as paints and solid-color stains; (2) semi-transparent
stains; (3) natural finishes such as water-repellents and water-repellent
preservatives; and (4) oils. Wood preservatives and fire-retardant coatings may
also be classified as finishes in some respects but are not within the scope of
this publication. The expected service lives of different exterior finishes for
cedar siding and trim are summarized in a
table.
If there is uncertainty over whether to use a water-repellent preservative or
a stain, first apply a water-repellent preservative. It is possible to switch to
a semi-transparent stain when the wood surface needs to be refinished. Even if
the cedar wood surface has been maintained with a water-repellent preservative
for many years, an oil-based semi-transparent stain will perform satisfactorily
Opaque finishes
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Paint provides the most surface protection against weathering
and wetting by water while providing color and concealing some of the
wood's characteristics. Although paint can reduce wood's absorption of
water, paint itself is not a preservative.
Alkyd oil-based primers usually offer the best shield against
discoloration by water-soluble extractives. Latex paint, particularly 100%
acrylic formulations, remain more flexible with age and are better able to
accommodate dimensional changes by stretching and shrinking with the wood.
Solid-color stains are opaque finishes with fewer solids than
paint. Available in a wide spectrum of hues, solid-color stains obscure
the woods true color but allow some of the natural characteristics and
texture of cedar to remain. Solid-color stains perform best on textured
surfaces. They are non-penetrating and, like paints, form a film. A
stain-blocking primer should be applied first, followed by a 100% acrylic
latex-based top coat.
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Natural finishes
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Water-repellent preservatives of some types are formulated with
non-drying oils. These oils penetrate the wood to protect it against
degradation. The cedar wood surface may remain oily until the finish
absorbs, which may take several days.
Water-repellents and water-repellent preservatives may be applied to
cedar used above ground. These formulations reduce water absorption in the
short term. The addition of a fungicide that inhibits the growth of mildew
and decay fungi will further increase wood's durability.
A low-wax-content water-repellent preservative applied to newly-milled
cedar as a single-coat pre-treatment before painting may help reduce
discoloration caused by bleeding of water-soluble extractives.
Semi-transparent stains may be latex or oil-based. The
semi-transparent nature of the stain, due to its low solids content, does
not block all ultraviolet radiation and some will reach the wood's
surface. Latex stains do not penetrate the surface and are not as durable.
Caution: Transparent, non-flexible, film-forming finishes such
as lacquer, shellac, urethane, and varnish are not recommended for
exterior use on cedar. Ultraviolet radiation can penetrate the transparent
film and degrade the wood. Regardless of the number of coats, the finish
will eventually become brittle, develop severe cracks and then fail.
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