Finishes for Western Red Cedar
If you choose to finish your Western Red Cedar, it should not be left unﬁnished and exposed to direct sunlight and moisture for any significant period of time prior to stain or paint application. Weathered surfaces, even if only exposed to the elements for a few weeks, will compromise Western Red Cedar’s ability to hold a paint or solid stain. The longer the period the Western Red Cedar is left to weather, the more rapidly the ﬁnish may fail.
Natural coloration of newly milled cedar can be retained by applying ﬁnishes that contain ultraviolet blockers. Finishes containing both an effective mildewcide and ultraviolet protection are recommended. Since these ﬁnishes contain a low percentage of solids, they tend to require higher maintenance. Penetrating oil-based stains or light-pigmented natural tones can also be applied to provide uniform color and wood protection.
Choice of Finishes
The choice of an exterior wood ﬁnish for Western Red Cedar depends upon the desired appearance and the degree of protection required. 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. Western Red Cedar’s excellent ﬁnishing characteristics cannot compensate for finishing products that are unsuitable, of inferior quality, or improperly applied. Exterior finishes perform best when the coating is applied to all surfaces (face, back, edges and ends).
In general, ﬁnishes for Western Red 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 transparent stains; 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 Western Red Cedar siding and trim are summarized below.
|Figure 1: Suitability and Expected Service Life of Exterior Finishes on Western Red Cedar Siding & Trim1 |
|Finish ||On Planed Smooth WRC2 ||On Textured WRC |
| ||Suitability ||Expected ||Suitability Life (yrs) ||Expected Life (yrs) |
|Paint3 ||High ||Up to 10 ||High ||Up to 12 |
|Solid-colour Stain ||Moderate ||3 to 5 ||High ||4 to 6 |
|Bleaching Oil ||Moderate ||3 to 5 ||High ||5 to 6 |
|Semi-transparent stain4 ||Moderate ||1 to 3 ||High ||2 to 4 |
|Water-repellent presertative and oil5 ||High ||1 to 2 ||High ||1 to 2 |
1Data compiled from research observations. Expected lifetime predictions are for an average location in the continental United States. Expected life will vary in extreme climates or exposures such as desert, seashore, and deep woods or according to the building’s orientation
2Vertical grain cedar
3Expected life of two coats: one primer and one top coat. Applying a second top coat will increase the life of the coating
4Follow manufacturer’s recommendations for the number of coats
5Development of mildew on surface indicates need for cleaning and possible refinishing
You Get What You Pay For
Remember, when purchasing a finish for your Western Red Cedar project it is always best to use a top of the-line product from a supplier you know and trust.
Western Red Cedar contains water-soluble extractives that are responsible for its attractive color, exceptional stability and natural decay resistance. However, these extractives may discolor latex paints and solid-color stains unless a primer coat is used that is specifically formulated to help control extractive bleeding. These stain-blocking primers are available in alkyd-oil and water-based formulations. Alkyd-oil based primers usually offer the best shield against discoloration by water-soluble extractives. The label on the container should indicate that the coating is recommended for use as stain-blocking primer for Western Red Cedar.
Paint provides the most surface protection against weathering and wetting by water, while providing color and concealment of some of the wood’s characteristics. Although paint can reduce wood’s absorption of water, paint itself is not a preservative.
Paints of all types such as: water-based paints, acrylic (latex), acrylic enamel and solvent based paints (alkyd and oil-modified) are suitable for Western Red Cedar. However, test results show that good quality latex paint maintains its mechanical adhesion through dimensional changes of the wood during wet and dry moisture cycles. For this reason, finishes with high elasticity generally maintain adhesion better than brittle finishes during extended periods of exposure to outdoor weathering.
These are opaque ﬁnishes with fewer volume solids than paint. Like paints, solid-color stains protect Western Red Cedar against ultraviolet light degradation and moisture. They are available in a wide spectrum of hues which obscure the wood’s true color but allow some of the cedar’s natural characteristics and texture to remain. These finishes are non-penetrating and, like paints, form a ﬁlm. A stain-blocking primer should be applied ﬁrst, before applying the solid color stain. Solid color stains are available as latex or oil based formulations.
Solid-color stains have been developed that reveal the wood’s grain. These are known as semi-solid stains and their effect on the appearance of wood lies between those of solid color and semi-transparent stains, as described below.
Many users of Western Red Cedar prefer a finish that preserves the wood’s natural color and appearance. To maintain the natural look of Western Red Cedar that is exposed outdoors, regular maintenance will be required. The following products provide varying degrees of protection against weathering while maintaining the cedar’s natural beauty:
These stains do not alter the appearance of the cedar. They only slightly modify the color (tone) of the wood. Transparent stains are similar in composition to semi-transparent stains, but they contain fewer pigments. Transparent stains formulated with a fungicide that inhibits the growth of mildew and decay causing fungi will further increase the wood’s durability. Waterborne and solvent borne formulations are available; however these unpigmented or lightly pigmented finishes provide limited protection against the sun’s ultraviolet light and moisture related damage. As such, they require frequent refinishing. Transparent stains are, however, easily refinished with minimal surface preparation.
Solvent borne oil-based semi-transparent penetrating stains penetrate the wood surface, are porous, and do not form a surface film like paints. These finishes are the best choice for Western Red Cedar, which is fully exposed to the weather, when a natural look is desired. Although these stains can be used on both smooth and textured Western Red Cedar, they will perform much better and last longer when applied to a textured surface. These stains contain pigments which provide color – including cedar tones – and greatly increase the durability of the finish by protecting the cedar surface, to some extent, from the damaging effects of the sun’s ultraviolet rays. Service life on siding applications may vary from 3-6 years depending on the cedar surface texture, quantity of stain applied, and the intensity of the sunlight on the wood surface.
Latex semi-transparent stains are similar in appearance to the solvent borne stains; however their look is achieved by the formation of a thin film with little penetration. This film is often not thick enough to provide the same durability as solvent borne stains and tends to degrade by flaking from the wood’s surface. Refinishing cedar that has been coated with a latex semi-transparent stain may require more substantial surface preparation. Currently, efforts are underway by many stain manufacturers to develop water-borne stains that penetrate cedar. However, to date, moderate success has been experienced in duplicating the properties of traditional oil-based, solvent borne, stains. As increasingly restrictive environmental standards reduce the availability of solvent borne stains, ongoing research suggests that penetrating, erodible latex semi-transparent stain finishes for cedar will be available in the near future.
Note: Transparent, non-ﬂexible, ﬁlm-forming ﬁnishes such as lacquer, shellac, urethane, and varnish are not recommended for exterior use on Western Red Cedar. Ultraviolet radiation can penetrate the transparent ﬁlm and damage the wood. Regardless of the number of coats, the ﬁnish will eventually become brittle, develop cracks in the coating film and then fail.