Photo: Visual Works SPS; courtesy of Western Red Cedar Lumber Association

Transparent stain on protected Western Red Cedar makes a dramatic visual statement on this award-winning commercial showroom.Project: IKOI Showroom. Location: Kakogawa-city, Hyogo Prefecture, Japan. Architect: Shoji Keisuke Atelier.

Western Red Cedar (WRC) has been a preferred and appealing choice for many buildings over the past 150 years for a lot of good reasons related to design, construction, and maintenance. WRC products come from trees grown in forests in the Pacific Northwest area of North America. They are routinely used in buildings across the country and around the world because of their warm, natural, aesthetic appeal and well-known durability and stability. Like all wood products, though, they benefit from proper finishing. Selecting the best type of finish will depend on several factors such as the use, (lumber or finish carpentry) application (interior or exterior), geographic location (climate, coastal, inland), and building design (residential, multifamily, commercial). This course focuses on the range of finishing choices for WRC and the factors that contribute to making the most appropriate finish selection. In so doing, architects can help building owners and managers achieve realistic expectations about final appearance, required maintenance, and ongoing benefits.

DESIGNING WITH CEDAR

Western Red Cedar (WRC) is a proven, well-known, and versatile building material. On building exteriors, it is a durable and resilient choice for siding, trim, soffits, decking, and outdoor structures. For building interiors, it provides a desirable aesthetic for wall paneling, wainscotting, ceilings, and as a great complement to a variety of building systems including mass timber structures. Given this range of uses, architects, interior designers, building owners, and facility managers have been drawn to incorporate Western Red Cedar into their projects for some specific reasons. These include:

• Appearance: Western red cedar is real wood with the corresponding authentic appearance of wood. Its grain and natural color have helped it to become regarded as a superior aesthetic imbued with decidedly crisp, yet superbly rich, tonal properties.
• Durability: Western red cedar is well known for its longevity and durability due to the natural make-up of the wood. It has been found to be naturally resistant to rot, decay, and insect attacks.
• Sustainability: While other building materials generate greenhouse gases, western red cedar trees remove greenhouse gases from the atmosphere. Further, unlike many manufactured or composite materials, WRC is fully biodegradable at the end of its useful life. Perhaps one of the best-known sustainability attributes of WRC is that it is a renewable resource when harvested and re-planted using sustainable forest practices. In fact, WRC in North America is sourced from some of the most sustainably managed forests in the world.
• Versatility: WRC offers a wide range of sizes, surface textures, grades, and profiles –both standard and custom. Therefore, it is easy to incorporate into a wide range of design schemes and patterns.
• Profiles: A virtually unlimited variety of common and specialty profiles of cedar siding, boards, and trim are made to suit different design and construction needs. These include beveled, lapped, tongue and groove, and board and batten applications all in various thicknesses and profiles for vertical and horizontal siding, paneling, and trim board applications.
• Grades: Recognized, independent agencies use grading systems to identify different “Appearance Lumber Grades” as distinct from structural lumber grades for cedar. These grading systems use terms like “Clear Vertical Grain Heart”, “A”, “B”, “Rustic,” “Select Knotty,” and “Architect Knotty” among others. The word “Heart” in the case of grading cedar refers to the inner wood in a tree as opposed to the narrow outer sapwood between the heartwood and the bark.
• Surface Texture: The surfaces of cedar products are available with a smooth surface, a rough-sawn appearance, or a rougher-headed texture, any of which can be specified to suit different project needs.
• Fasteners: High-quality fasteners that prevent staining and discoloration (i.e. stainless steel, aluminum, double hot-dipped galvanized) help to assure that both the appearance and the performance are maintained over time.
• Finish: Unlike some other wood species, Western Red Cedar is pitch and resin-free. This means it’s ideal for accepting and holding a wide range of wood finishes.

Overall, the most appealing characteristics of Western Red Cedar include its outstanding dimensional stability, fine texture, and being free of pitch and resin. These characteristics all contribute to its exceptional ability to accept and retain many different types of finishes. With all of these attributes in mind, we will focus next on the different types of finishes used on WRC to enhance its appearance and function when installed and over its useful life.

Photos: David Papazian; courtesy of Western Red Cedar Lumber Association

Cedar-toned semitransparent stain offers great visual appearance and durability against weather and ultraviolet sunlight. Project: Hilltop House. Location: Portland, Oregon. Architect: Giulietti Schouten Weber Architects GSW/A.

TYPES OF WOOD FINISHES

The choice of how to finish Western Red Cedar in any project should be based on an understanding of the different options and their suitability not only for design aesthetics but for its realistic durability before they need to be re-finished or re-applied. While it is true that Western Red Cedar can be allowed to weather naturally and create its own gray coloring or patina, it is more common to provide a protective finish. Such coatings help ensure maximum performance so that the natural beauty of the wood can be maintained or enhanced.

First, there are some overall things to keep in mind. In general, solvent-borne alkyd/oil-based stains are best for penetrating the wood and providing good performance. They have become harder to find and are simply not available in some locations where there are restrictions on VOC emissions. With that in mind, it is good to be aware that water-soluble oils or strictly latex stains have pigments that sit on the surface of the wood, rather than penetrate into it. These pigments absorb ultraviolet light, which would otherwise change the color of the wood. The rest of the ingredients in these products provide needed water repellency which helps protect the wood and resist mold and mildew growth. Whether oil-based or not, the building design and the degree of exposure to weather will impact the service life of all finishes. While the Western Red Cedar may hold up just fine, the finishes may not.

The following is a summary of the most common types of wood finishes used on WRC.

• Clear or transparent finishes: These coatings do not add any color or alter the appearance of the cedar, they only slightly modify the color (tone) of the wood. They do provide some protection for the wood surface. It is important to recognize that they have short service lives when exposed to sun and weather so are better suited to protected areas. Transparent stains, if formulated with a fungicide/mildewcide will inhibit the future growth of mildew and fungi, which will further increase the wood’s durability. Waterborne and solvent-borne formulations are available, but these unpigmented or lightly pigmented finishes provide limited protection against the sun’s ultraviolet light and moisture-related damage. As such, they require frequent reapplication. Transparent stains are, however, easily reapplied with minimal surface preparation.
• Semi-transparent finishes: These provide some color but still allow the grain of the wood to be visible. If solvent-borne, oil-based, semi-transparent stains are available, they penetrate the wood surface, are porous, and do not form a surface film like paints, stains, and latex formulas. These oil-based finishes are usually the best choice for natural-looking Western Red Cedar when it is fully exposed to the weather. Although these stains can be used on both smooth and textured Western Red Cedar, they perform much better and last longer when applied to a textured surface. These stains contain pigments that provide color–including cedar tones–and greatly increase the durability of the finish by protecting the cedar surface from the damaging effects of the sun’s ultraviolet rays.

  If latex semi-transparent stains (i.e., non-oil based) are used, they are similar in appearance to 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 surface preparation.

• Solid color stains: 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. Oil-based solid color stains should not be applied over latex primers. Solid-color stains have been developed that reveal the wood’s grain and are known as semi-solid stains. Their effect on the appearance of wood lies between those of solid color and semi-transparent stains.
• Paint: Opaque, solid color paint can be used to completely cover the wood surface. Recognize, though, that 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 a stain-blocking primer for Western Red Cedar. Virtually unlimited solid colors are available from all paint suppliers to then cover the primer.
• Bleaching/Weathering Cedar: If a truly uniform grey appearance is desired on exterior WRC, then this effect can be achieved by the use of commercially prepared bleaching or weathering products. These are essentially water-repellant finishes containing pigments and other additives that are most effective on textured cedar. To maintain this look, bleaching or weathering products may need to be re-applied periodically. Although the natural weathering effect is usually only “skin deep” (less than 1 – 2mm), with the cedar largely unchanged beneath, extra care must be given to the design of the project, the installation of the cedar, and routine maintenance. A proper application could be reasonably expected to last 3 to 5 years on smooth WRC and 5-6 years on textured.
• Other finishing products: While the five options above are used for exterior applications, there are some other finishing options that are only suitable for building interiors where weather and UV exposure are not a concern. These include bleaches, clear waxes, Danish oils, and clear plastics (non-yellowing), as well as lacquers, and varnish. These are discussed more in the interior finishing section of this course.

Photos: Meghan Montgomery/Built Work Photography courtesy of Western Red Cedar Lumber Association

Dark semi-solid stain is combined with semi-transparent stain and painted features to create a great deal of visual interest in this urban environment. Project: Cedar Speedster. Location: Seattle, Washington. Architect: Weber Thompson