Finishes for Western Red Cedar should not be left to weather

Here the Western Red Cedar Lumbar Association (WRCLA) provides a handy guide to finishing cedar.

Even though cedar weathers over time to an attractive silver-grey patina that has a certain
architectural appeal, researchers and wood scientists strongly recommend that some form of
protective finish should be applied to prevent surface degradation.
Weathered surfaces provide a poor substrate for finishes. Even a few weeks of exposure will
decrease cedar’s ability to hold a finish. Once the finish-wood interface fails, the coating will debond, blister, crack, flake or peel. The longer the period of weathering, the more rapidly the finish may fail.
Fortunately, cedar accepts many types of finishes. The choice of an exterior wood finish for
cedar depends on 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.
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).
Finishes for cedar can be grouped into four categories:

Opaque coatings, such as paints and solid
colour stains.
• Semi-transparent stains.
• Natural finishes, such as water repellents and water repellent preservative oils.
• Wood preservatives and fire retardant coatings may also be classified as finishes in some respects.

Surface Preparation
The surface condition of the wood can substantially affect the performance and the life expectancy of the finish. New wood, such as cedar siding and trim should be protected from the weather before, during and after construction.
It is rarely necessary to carry out extensive surface preparation providing the wood has not
weathered for more than two weeks and is clean and dry. If it has been contaminated by dirt, oil and other foreign substances, they must be removed.
For smooth-plated, flat-grained cedar, some surface preparation may be desirable. On  flatgrained wood, the surface should be scuff-sanded with 50 to 60-grit sandpaper. This procedure will increase the coating’s performance, but will still give a smooth finish.
Surface preparation is not necessary for textured cedar. Weathered new wood that has been exposed to the elements for longer than two weeks may have a degraded surface that is unsuitable for painting. Preparing the surface by sanding, brushing and washing before applying the finish is recommended.
Paint finishes must be removed if the old surface is severely peeled, blistered or if rossgrain
checking has occurred because of excessive paint build up. The removal of a film-forming finish is also necessary if a penetrating stain or water repellent finish is applied to a previously painted or solidcolour stained surface.
Finishes can be removed by sanding, wet sandblasting, pressurised water spray, electrically
heated paint removers and chemicals. Although they are quick and easy, sandblasting and
pressurised water spray are not recommended unless extreme care is taken to avoid damage to
the wood’s surface. Special precautions to ensure worker safety must be taken if the old paint contains lead.
Weathered water repellent preservative finishes should be cleaned with a non-ferrous bristle brush to remove loose fibres and dirt. If the surface is soiled, it may be scrubbed with a
mild surface solution. If mildew is present, it should be controlled, after which the surface
should be thoroughly rinsed and allowed to dry completely before refinishing.

Application of exterior finishes
How a finish is applied to cedar is as important for durability and good performance as is the combination of finish and substrate chosen for the job.
Finishes can be brushed, rolled, sprayed or applied by dipping. The application technique, the
quantity and quality of finish applied, the surface condition of the substrate and the weather
conditions at the time of application can substantially influence the life expectancy of the
Paints of all types, such as vinyl-acrylic, modified-acrylic and oil-based top coats are all
suitable for cedar, but tests show that good quality, 100% acrylic formulations work best.
Water-repellant preservatives should be used only on newly manufactured bare cedar, on restored bare cedar or on cedar previously treated with the same type of product.
Application of preservative by brush, pad or roller followed by thorough back-brushing is
also effective. When used as a natural finish, the surface life of a water repellent is only one or two years, depending on the wood and the exposure. Treatments on textured surfaces
generally last longer than those on smooth surfaces.
Semi-transparent, oil-based penetrating stains may be applied by brush, spray, pad, or roller. Brushing will usually give the best penetration and performance. Spray or roller application followed by back brushing is also an acceptable method of application.
Solid colour stains, acting much like paint, may be applied to cedar by brush, roller, or
pad (brush application is usually the best). One coat of solid-color stain is only marginally
adequate on new wood, while a prime coat with a top coat will always provide better protection and longer service.

Interior finishes
Finishes for cedar paneling, posts, beams and joinery generally require less protection
than cedar exterior finishes. Interior cedar finishes are used for decorative purposes to
complement the inside and ensure the surface is easily cleanable.
Nevertheless, there is a vast choice of finishes, though paint is an unlikely choice as an interior-finishing medium, as it tends to hide the timber’s intrinsic beauty. Transparent
finishes include clear wax, Danish oil, varnish stains and clear vanish.
Stains, whether they are transparent, semi-transparent or opaque, maybe used indoors to provide decorative colour. Given that there is less need for protection, lightly pigmented products can usually provide the required tone without hiding the natural grains of the wood. One brushed coat is normally sufficient.