Types of Wood

Wood is the preferred material for decks. Not only is wood beautiful, it is also stable, durable, and easy to work with. Wood is susceptible, however, to water damage and should be checked regularly. Boards that are split, cracked, or have raised nails indicate a possible problem with moisture penetration. Wood is also a porous material, like skin; and like skin, wood pores can become clogged and deteriorate. One way to prevent problems with your wood is to have it sealed and maintained. Below is a list of commonly used woods for deck construction.

Types of Wood

Cedar: The wood from this large, coniferous evergreen tree is a popular favorite for decks. It not only looks and smells wonderful, it is also extremely durable. The texture of cedar is soft, and the grain of cedar is intricate and beautiful. Cedar produces natural tannins that are thought to be naturally resistant to insects. These tannins, however, can spot, especially after rainfalls, and this continues until the wood becomes fully acclimatized (about three years). Sealer colors that work particularly well with cedar are the natural redwood or cedar tinted, or clear. These sealers allow the natural grain of the wood to show through, while at the same time protecting the wood through a color tint.

Redwood: Used frequently in timber construction, redwood is (as the name suggests) a reddish wood. Outside of the color, redwood is very similar to cedar.

Pressure- Treated Pine: This term refers to wood that has been chemically treated to ward off insects and rot. Cedar and redwood are never treated. The drawbacks to using pressure treated wood are rapid discoloration, prone to splitting, and many chemicals are in the wood that can discolor it. As with all woods, it is always best to have your pressure treated wood seasoned, cleaned, and sealed so that these natural drawbacks can be avoided.

Pine: This long-needled tree also has wood that is very popular in deck construction. Pine varies from very soft wood, as with the white pine, to very hard wood, as in the long leaf pine. Usually pressure treated for deck construction, pine is very versatile, cheaper than cedar or redwood, and dependable. Depending on personal preference, pine works well with any color sealer. As with cedar, there are natural colors that can enhance the natural grain and color of the wood.

RECONSTITUTED WOOD PRODUCTS 

Hardboard, a relatively heavy type of fiberboard, is a popular siding product. Continuous film coatings are recommended on this substrate, not stains. However, water soluble extractives in the product may leach through paints causing a discoloration. Acrylic latex stain blocking primers and one or two acrylic latex topcoats are recommended. Pre-primed hardboard must be primed again on-site before top coating. Storage of the product under fluctuating moisture conditions will cause a dislodging of the surface fibers (the primer cannot inhibit this) resulting in an unstable surface. Re-priming will help stabilize the surface and will help in avoiding early paint failure.

Other reconstituted products, including waferboard, strandboard. (OSB) and flakeboard, are difficult to coat successfully unless the surfaces are treated or overlaid specifically for exterior usage. In this case continuous film coatings are usually recommended.

CEDAR AND REDWOOD SIDING

Western red cedar and redwood generally exhibit the best characteristics for holding continuous film coatings. However, recently being marketed is a grade of cedar siding which comes from more immature growths and contains a mixture of grains (mixed grain) involving both flat and edge grain. This siding is rather unstable and continuous film coatings are a risky choice, even though the product is marketed under the highly regarded "cedar" designation. Other products are anticipated as new growths of timber and sub-species are harvested, and coatings specifiers must remain aware of these new entrants into the market place.

Water soluble extractives are present in cedar and redwood, and may leach through coatings as they become activated by moisture. These may show up as tobacco colored stains, particularly on light colored stains or paints. They may be controlled with rather good success by using an acrylic latex stain blocking primer or an exterior oil based primer before painting, but may cause discoloration on light colored semi-penetrating or solid color stains.

PORCH AND DECKING

Decks are subjected to particularly severe exposure, plus abrasion from foot traffic. The horizontal or flat surfaces receive maximum sunlight and moisture collection. Resultant swelling and shrinking of the wood severely overstrikes any continuous film coating, resulting in cracking and peeling. These coatings are not recommended for these surfaces. Water repellents and semi-penetrating stains are recommended coatings. They require frequent refinishing, but it is an easier task than the sanding and scraping needed to prepare paints or solid stains for refinishing. Latex products are to be avoided where water can collect on flat surfaces.

PLYWOOD PRODUCTS

Exterior plywood, faced with southern yellow pine, Douglas fir or western red cedar are frequently used for exterior surfaces, in both smooth and roughhewn surfaces. Smooth sanded plywood is not recommended for siding, although it is used extensively for soffits where it is protected from sunlight and moisture. Plywood, especially when subjected to sunlight and moisture, develops surface checks (cracks). These allow moisture to enter, causing swelling and shrinking resulting in a very unstable surface which will overstress a paint film, causing cracking and peeling. Alkyd/oil paints will show early failure. Top quality acrylic paints will usually fair somewhat better, and are particularly suitable for soffits. However, since flat grain is predominant in most plywood products, continuous film coatings, particularly on rough surface plywood, are less suitable than semi-penetrating coatings.

ALUMINUM AND VINYL SIDING

Aluminum siding finishes will eventually break down, like the finish on your automobile. When this surface becomes chalky, it should be cleaned thoroughly and top quality acrylic latex house paint applied.
Vinyl siding should weather at least eight years before painting with a top quality acrylic house paint. Do not use a darker color than the original siding or the siding will expand and buckle from the additional heat absorbed by the darker siding from the suns rays.

WOOD SHAKES AND SHINGLES

Edge grain heartwood cedar shingles/shakes are preferred over flat grain and/or second growth timber products. Moss, algae and lichens must be removed and controlled. Clear water-repellents may be used, but have a very short lifespan. Roofs should never be coated with a continuous film coating since these tend to trap mois-ture which leads to early coating failure and promotes decay. Semi-penetrating stains are recommended for roof surfaces, but light colors may discolor from water soluble extractives in the cedar. Sid-ing shakes or shingles may be coated with either penetrating or solid color stains. Dipping is the preferred application method to protect the backs of the shingles from moisture collection. If this is not practical, brushing is the next best application procedure.

WOOD CHARACTERISTICS AFFECTING COATABILITY

Coatings fall into two categories. Continuous film coatings are primers, paints, heavy bodied and solid color stains which form a solid, unbroken film over the surface. Semi-penetrating stains, the second category, penetrate the surface of the wood to a great extent resulting in very little surface film. Wood products may be success-fully coated by one, or both, or neither of these coating types, de-pending on their characteristics and how they are manufactured.

Wood species are characterized by their density (weight), presence of early wood or latewood, their texture (cell structure) and the extent of extractives including water soluble color, pitch and oil. Generally, higher density woods (hardwoods) are less suitable for exterior use than less dense softwoods such as cedar and redwood.

Manufacturing and grading of wood products also determine their suitability for accepting coatings. Surface textures, knots or other defects, and moisture content greatly affect coatability. How the product is cut from the log, to yield edge grain or flat grain boards, often dictates what type of coating can be used successfully on the product. Most standard lumber grades contain a high percentage of flat grain, whereas premium grades are predominantly edge grain. Flat grain areas tend to swell and shrink more, are relatively unstable, and will not hold continuous film coatings nearly as well as the more stable edge grain surfaces.