For help, we discussed this matter with Paul Mackie of the Western Red Cedar Lumber Association (WRCLA).
Reasons For Painting Cedar SidingQ: Are there instances when you would recommend painting over other types of surface treatments?
A: The type of finish selected is driven by style preference, and truly what one wants the siding to look like and frequency of re-finishing. Western Red Cedar siding finished on all six sides with a stain blocking primer and top coated with 100% acrylic latex paint has the longest expected service life for the coating system. Factory applied finishes of this type are available in most market areas.
Q: This begs the question, “What’s the purpose of installing Western red cedar siding if you’re going to paint over it?” Does cedar siding have benefits that extend beyond its pretty face?
A: 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’s natural, sustainable and a renewal product. It’s easy to install and is available in almost unlimited sizes and patterns for those that want a unique ‘look’.
Q: With regard to painting, does it make a difference whether the cedar is fresh vs. old? It’s my assumption that new cedar may be impregnated with extractives that may prevent paint adhesion. A Forest Service recommendation says to wait up to 16 weeks before painting. What’s your take?
A: Many don’t know that Western Red Cedar has a natural resistance to rot, decay and insect attack. For best results if paint is the selected top coat, fresh siding should be pre-primed on all six sides with a stain blocking primer and top coated with 100% acrylic latex paint. Alkyd-oil primers are recommended, but one may choose a high quality latex primer as long as it contains stain blockers.
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 50% of its ability to hold a film forming coating system like primer and paint.
There is a sample of Western Red Cedar siding on the test fence at the testing lab in Madison, Wisconsin. It was pre-primed on all six sides (including the ends), top coated with two coats of paint and placed in a frame. It has never been re-coated, shows no degradation of the coating system and has been on the test fence for more than 24 years. Other samples were allowed to weather for 3 months, 6 months, 9 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 starting at the end grain where the siding abutted trim because the ends of the siding had not been primed.
Q: The longer cedar weathers prior to painting, the more rapidly its eventual paint coat will fail. But is there a point when red cedar is simply too weathered and old to paint...ever?
A: Surface preparation is key to success when dealing with weathered wood. The siding must be free from mold, mildew and dirt. Loosened (photo degraded) 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.
Cedar Surface Properties and Priming Cedar Before PaintingQ: While this is a U.S. Forest Service factoid, not from WRCLA -- do you know why vertical grain cedar is supposed to hold paint better over long periods of time? Is it because a horizontal grain doesn’t shed water as well?
A: Vertical grain cedar, because of cell structure orientation 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 resawn face. Considering our involvement with the Joint Coatings Committee that works closely with the Forest Products Testing Lab, I suspect that the factoid that is cited is dated information.
Q: WRCLA recommends priming before painting. What will happen if you paint cedar siding without priming?
A: A two coat system, primer with a paint top coat, will have a significantly longer service life than will a single coat of paint (or solid stain). Paint without a primer applied to weathered wood will have adhesion difficulties.
Q: Would the same hold true for these exterior paints that claim to be self-priming (paint and primer, all in one)?
A: I have not seen any test data on the supposed 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.
Painting Cedar SidingQ: “Good quality latex paint” is recommended by WRCLA. Can you expand beyond that?
A: We recommend the use of 100% acrylic latex paint as they are proven to have longer service lives than blended products.
Q: Are there any paint manufacturers you can suggest that work better on cedar?
A: We recommend the ingredients that primers and paints (and other finishes as well) should contain and do not endorse specific manufacturers or their products.
Q: Are there any painting techniques you can suggest that work better for cedar siding? For instance, spraying vs. hand-brushing, etc.
A: For refinishing, hand-brushing is always preferred. If one chooses to spray apply, best results will be achieved by back brushing the finish during application. It is likely that hand-brushing will get more paint on the wood.
* For the purposes of this interview, the abbreviated terms “cedar” and “red cedar” refer to the same product: Western red cedar.