Outdoor Building Materials and How To Coat Them (Part One)
Blue Door Painters, DC area coatings contractor, discusses the nature of various outdoor building materials – and the coatings that protect them.
My Deck is Made of . . .
. . . “SPF”
Hopefully not. In the lumber world, ‘SPF’ does not refer to sunscreen: it is an acronym for ‘Spruce-Pine-Fir’, three kinds of lumber used interchangeably by builders for a variety of purposes. Depending on your region, the exact species of SPF wood will vary (Red Spruce, Jack Pine, and Balsam Fir typical in the west; White Spruce, Englemann Spruce, and Lodgepole Pine in the east, among many others), but all of them share similar characteristics that make them ideal for building. They all come from softwood conifers that are cheap to grow and harvest, and the finished lumber is reliably strong and workable.
The problem is, this type of lumber is NOT suitable for exposure to the elements. While buildings framed in SPF hold up perfectly well when the wood is protected by layers of insulation, siding, and drywall, exterior decks or fences constructed with SPF will rot at lightning speed. The quick-growing SPF conifer species produce lumber with wide, hungry pores which suck in ambient moisture and invite all types of rot, against which the lumber, adapted to a dry climate, has no natural defenses. Coating this kind of lumber, while it can buy you time, will not halt this deterioration completely.
So the best advice is, don’t build any outdoor construction out of SPF. If it’s too late, and you already have an SPF deck or fence that you won’t or can’t replace, your only hope is to coat it very aggressively, and re-coat it frequently as part of your routine upkeep. Consider using a few layers of stain followed by a fully waterproof clear-coat sealant, or select a hardy, weatherproof primer paint followed by a few layers of water-resistant topcoat. Make sure that all six sides of the wood are coated. The end grains, where all of the pores are cross-cut and exposed, are the most vulnerable, and it is well worth giving them a few extra layers if you want to hold your own in the battle against the elements.
. . . Pressure – Treated (PT) Lumber
If your deck is made of pressure-treated lumber, then you are in good company; pressure-treated wood has been one of the most popular outdoor building materials since the development of pressure-treatment in the 1940s. Frustrated with the vulnerability of the otherwise-convenient softwood lumber, Dr. Karl Wolman invented a procedure that drove artificial preservatives – antimicrobial and anti fungal chemicals – deep into the pores of the wood, so that moisture-borne rot could not easily take hold. The variety of softwood used for pressure treatment varies by your region – Southern Yellow Pine is the most common species used in the Washington, DC area – and the specific chemicals used to protect the wood varies based largely on when your deck was built. Until 2003, most companies used chromated copper arsenate to pressure-treat their wood, since it was (and remains) the most effective preservative available on the market. However, CCA’s toxicity to microbes and fungus extends to animals and children, and over the years a great deal of concern was raised over the long-term health effects of exposure to wood treated with CCA. The chemical has now been discontinued for use with residential lumber, and modern pressure-treated lumber is infused with alternative, less toxic chemicals.
Coating a pressure-treated deck or fence is of the utmost importance, both to extend the life of the wood and to protect against exposure to the preservatives. If you have an older deck, the EPA recommends applying a penetrating oil-based finish to block human exposure to CCA. Many companies offer clear preservative coatings that are intended for use on fresh pressure-treated wood; these sealants should be used immediately to guarantee ideal protection. However, it is essential that you find a product intended for use on fresh pressure-treated wood, and you wait one to two months before applying any further paint or staining. The reason is that fresh pressure-treated wood has moisture in it from the PT process that takes a while to dry out, and if you coat it while your project is still wet, both the coating and quite possibly the wood itself will be destroyed. Once you have sealed your fresh PT project and given it adequate time to dry, staining or painting your wood with products intended for use with PT wood will give it the extra protection needed to ensure true longevity.
Stay tuned for the skinny on Redcedar, Redwood, and Composite Decking.