One benefit of installing cedar siding is the beauty of its natural finish. Red cedar has a natural resistance to rot, decay, and insect attack. Still, some homeowners may desire—or feel the need—for painting cedar siding. According to Paul Mackie at the Western Red Cedar Lumber Association (WRCLA), red cedar siding that has been finished on all six sides with a stain-blocking primer and top coated with 100-percent exterior acrylic-latex paint has the longest expected service life of any coating system. Factory-applied finishes of this type are available in most market areas where cedar siding is sold. But installed cedar siding that is painted on one to four sides can still provide excellent protection.
Choose the Correct Type of Paint For the Cedar
Exterior grade acrylic-latex paint is the most dependable finish in terms of protecting cedar. The type of finish selected is driven by style preference. For many owners, painted cedar siding is a particular style; it is not all about protection. In many markets, like New England for example, painted siding is the preferred look. Beyond that, Western red cedar has multiple advantages over other cladding options because it is natural, sustainable, and is a renewal product.
For best results, fresh siding should be pre-primed on all six sides with a stain-blocking primer and top coated with 100-percent acrylic-latex paint. Alkyd-oil primers are recommended, but one may choose a high-quality latex primer as long as it contains stain blockers.
Prime the Cedar Before You Paint It
It is strongly recommended that you go with the two-coat system for protecting your cedar siding. A primer with a paint top coat will have a significantly longer service life than will a single coat of paint or even a solid stain. Paint without a primer applied to weathered wood will nearly always have adhesion difficulties.
Brush the Paint Rather Than Spray or Roll
Hand-brushing is recommended. For refinishing, especially, hand-brushing is always preferred. If one chooses to spray the paint on the cedar, the best results will be achieved by back brushing the finish during application. With a porous material like cedar, the main idea is to apply a greater quantity of paint to the wood, and hand-brushing is the best way to accomplish this.
Choose the Optimal Window of Time For Painting Cedar
It is recommended that you paint within two weeks of installing the cedar. Make sure that you wait no more than 12 weeks.
Allowing fresh siding to weather for as little as two weeks negatively affects coating adhesion. Test results from the Forest Products Testing Lab (run by the USDA for the Forest Service), show that after 12 weeks of exposure to sunlight, cedar siding has lost half of its ability to hold a film-forming coating system like primer and paint. Another test at an experimental facility in Madison, Wisconsin involved a sample section of red cedar siding that was pre-primed on all six sides (including the ends), top coated with two coats of paint, and placed in a frame. The test section has never been re-coated and it shows no degradation of the coating system, though the test is over 25 years old.
Other samples were allowed to weather for three months, six months, nine months, and 12 months before being primed and painted. The longer the siding was allowed to weather, the sooner the coating system failed. And in all of those cases, it failed to start at the end grain where the siding abutted trim because the ends of the siding had not been primed.
Be Careful When Painting Very Old Cedar Siding
While extremely old cedar can be painted, it requires heavy preparation. Even then, the paint is not expected to last long. Surface preparation is the key to success when dealing with weathered wood. The siding must be free from mold, mildew, and dirt. Loosened (photodegraded) surface fibers, and any loosened remaining finish must be removed prior to re-finishing. Sanding is an option on smooth face siding and commercial strippers/restorers are available to accomplish this task.
Choose Vertical Grain Cedar If Possible
Because of cell structure orientation, vertical grain cedar absorbs alkyd-oil stain-blocking primers better than flat grain cedar. However, knotty cedar holds these primers well because most knotty cedar siding patterns have a textured or re-sawn face.
Use a Two-Coat System Rather Than Self-Priming Paint
The WRCLA has not seen any test data on self-priming paints. Factory finish warranties provided by primer and paint manufacturers apply to cedar siding that has one coat of primer and one or two top coats of paint. In other words, most field tests that demonstrate the efficacy of painted cedar have been performed only on the two-part painting system of primer that is allowed to cure, followed by a separate coat of paint. If at all possible, favor the two-coat system over the one-coat system.