Q: Why should my customer specify prefinished wood siding?
A: It's more economical! Prefinishing can cost as little as half of the price of a painting contractor painting on site. Your siding arrives at the jobsite protected from the elements. A recent U.S. Forest Products Laboratory study shows that as little as two weeks exposure to weather and sunlight will negatively affect wood siding's ability to hold a finish. Finishing in a controlled factory setting ensures the greatest penetration and uniformity possible with no brush laps or skips. The entire piece gets finished. Wood sidings are prone to seasonal dimensional changes, due to moisture content fluctuations. Finishing on site may cause "shrink back marks" as unfinished wood from under the lap appears.
Q: Does it matter if I use kiln-dried or green lumber?
A: One of the most stable softwoods, Western Red Cedar is nevertheless a natural material. Cedar siding can swell or shrink as it gains or loses moisture to reach equilibrium with the moisture content of the surrounding air.
In the Midwest, kiln-dried products are closer to the moisture levels of the final installation environment. Also, drier wood products are more receptive to finishes than unseasoned or green sidings. For this reason, kiln-dried sidings are recommended for prefinishing. (If required E. A. Allen Lumber will try to acclimatize "green" cedar products prior to finishing.)
Q: Does it matter which face is stained, rough or smooth?
A: Western Red Cedar is sold in a variety of patterns and grades, and the texture will be either rough (rustic) or smooth. Rough textured wood surfaces will absorb and hold more finish. The rough side is recommended in most cases.
Smooth textured wood surfaces are less absorbent and more difficult to build a surface "film" upon. For this reason, a minimum of two coats of a film-building finish are recommended for smooth sidings to be exposed outdoors. It is also recommended that the smooth face should be field finished after installation.
Q: What are the reddish brown stains on cedar sidings and trim?
A: Cedar owes its color and durability to what are called its "extractives." As moisture passes through the siding, water is being pulled toward the wood's surface as it evaporates. As this moisture migrates to the surface, it may carry dissolved extractives through the finish leaving a reddish brown deposit. Such discoloration may simply "wash down" with the weather, or may be washed from the surface by using a non-metallic brush and a solution of: two tablespoons of trisodium phosphate (TSP) or other detergent, 1 cup of bleach, and 1 gallon of hot, clean water. Brush on, then rinse thoroughly. Extractive discoloration on the surface finish may occur with either semi-transparent or solid finishes; with either solvent based oil or water-borne latex finishes.
Neither extractive discoloration nor mold/mildew growths are the fault of the lumber, the finish or misapplication of a finish. The culprit is excessive moisture and/or improper ventilation. By allowing the moisture to migrate to the exterior, cedar siding offers an advantage over vinyl or aluminum sidings which act as moisture barriers, trapping the condensation within the wall cavity and possibly causing conditions conducive to decay. See more about Extractive Bleeding.
More on Extractives
Q: Is staining the backside important?
A: "Back priming," or coating the backside on the same run in the factory, is a process we do on every bevel and board order at E.A. Allen Lumber. We believe this process will greatly reduce moisture content fluctuations, thereby enhancing a siding's performance. It will also help in avoiding cupping and prolonging the life of the finish. And, back priming can only be done before installation.
Q: Which is better latex or oil?
A: The two major categories of finishes used in the prefinishing process are latex and oil. Each has its own advantages which will dictate which to use in any particular application. Latex (waterborne) coatings are flexible, "breather-type" film finishes. Because latex coatings breathe allowing moisture to pass through, blistering is less likely to occur. They are available in solid (opaque) colors, semi-solid or semi-transparent colors. Oil or solvent based stains are brittle sealing type stains which work as a primer because of their ability to penetrate. They are available in solid, film-building, or semi-transparent penetrating formulations.
The U.S. Forest Products Laboratory and the Western Red Cedar Lumber Association (WRCLA) both recommended a two coat solid system as the best possible coating for exterior WRC sidings. The first coat should be a primer to seal in the water soluble extractives without forming a heavy film which could crack or peel. This should be followed by a second coat of a 100% acrylic latex, film-building paint or stain. E.A. Allen Lumber will warranty this two coat factory applied, solid system, for 15 years against peeling, cracking, blistering, flaking, and yellowing.
Q: What type of stain would I use if I want to see the knots & grain?
A: Semi-transparent stains are moderately pigmented stains which are intended to show the characteristics of the wood, such as grain and knots, through the color. They are thin and intended to penetrate the wood's surface without forming a film. By their nature they will not completely block out the ultra-violet rays of the sun, although for a time they may seal out water and offer some protection from degredation. They will wear off and require reapplication in a relatively short time. Solvent based oil stains penetrate the wood surface well, but new advances in water-based acrylic semi-transparent stains have made them the superior coating. Water-based semi-transparents are more resistant to mildew than oil, and Cabot is willing to warranty theirs for 5 years.
Note: Semi-transparent stains cannot be applied over previously finished woods (solid stains, paints, primers). The color will be affected by the texture and porosity of each individual piece of wood, thereby creating a lack of uniformity, the appeal of which is a matter of the customer's taste.
One coat of a semi-transparent should be sufficient. If a darker coloration is desired, two coats may be applied, but the second coat should be done while the first coat is still wet to avoid "self-repellency," which happens when a dry water-repellent finish repels a second coat.
Q: What kind of finish will last the longest?
A: Solid finishes offer more protection than semi-transparent because they block out UV light and moisture. Acrylic latex solid topcoat works the best on exterior sidings because they breathe out moisture and are flexible. Acrylic latex solid finishes should be applied over a penetrating tannin blocking primer when used on wood species which contain water soluble extractives, such as cedar, redwood or cypress. One coat of lightly pigmented solid finish color such as white or light gray, may not be sufficient to achieve a totally opaque film. At least two coats are recommended for maximum performance of any film building finish on exterior sidings.
Q: Can I put a Clear Wood Sealer on my siding to keep it looking natural?
A: Clear wood finishes generally have a limited life and they need to be reapplied frequently. Discoloration of the wood will be slowed, but will still take place. Repeated application may produce a waxy film which could repel a pigmented stain later if a color change is desired. Starting with a semi-transparent stain in the same tones as the original wood may be a better way to assure color retension and successful future reapplicaton results.
Q: Can I just let my cedar go gray naturally?
A: Many people desire the natural "weathered" look for their wood siding. The problem is that natural weathering will not be uniform, and probably will not achieve the desired appearance. The wood under eaves will not be weathered and the "backsplash" area may be much more weathered. Also, variances will occur from board to board and on different sun exposures (north vs. south side). To avoid this, bleaching and oil stains can be applied which will speed along the natural process and provide some uniformity. Most bleaching oils contain light gray pigmentation, a mildewcide and a water repellent to keep the wood from over darkening.
Q: What should I use on plywood siding?
A: The American Plywood Association recommends that opaque (solid) colors be applied to plywood sidings of any softwood species for exterior application. The use of semi-transparent stains is not recommended because the variations in the texture and porosity of face veneers from piece to piece will cause a lack of uniformity. Plywood sidings should never be left unfinished as weathering can lead to delamination and/or surface degredation.
Q: What kind of stain should I use on my deck?
A: Penetrating, non-film building oil-based satins or clear finishes are recommended on exterior wood decks. Semi-transparent or pigmented deck stains will last longer than clear wood finishes because the pigment provides an extra measure of protection. Deck boards should be thoroughly dry before staining and stained on all sides and end sealed after cutting to length in order to stabilize the moisture content and exclude moisture absorption from the underside.
Q: Should I back prime my deck boards too?
A: Yes! Moisture from under the deck and in the ground will be absorbed into the wood from the bottom. When the sun heats up the top surface of the deck, moisture will be drawn toward the finish and may diminish its longevity. Occasionally, this can even cause a penetrating, sealer type coating to peel, and bring the wood right up with it. Backpriming stabilizes the moisture content of deck boards and minimizes the absorption of additional moisture.
More FAQ's About Wood and Coatings Applications
Improve Performance of Painted Wood Sidings
Coating Performance vs. Weathered Wood |
