Q–I have asked three different people and received three different answers about cleaning and sealing my new wood deck. Is it necessary to apply a sealer to a brand new wood deck? Do you need to clean new wood before applying the sealer? What is the best method to clean wood decks?
I have had bad luck with sealers in the past. Is there one that resists mildew and algae? What is the best weather for cleaning and sealing decks?
A–I have gotten an abundance of conflicting advice, too. Out of curiosity, I frequently ask employees of home centers and paint stores how to approach deck cleaning and sealing jobs. I have yet to get the same recommendation from two different people.
What’s worse is there is much questionable information being distributed. It turns out that many traditional wood deck cleaning and sealing products and methods might not be best for your new wood deck investment.
Unprotected wood is attacked as soon as it is exposed to the sun’s ultraviolet (UV) rays as well as the water from snow, rainfall and dew. The UV rays actually blast apart the wood cells on a microscopic level. This damage permits water to penetrate deep into the wood.
Water can accelerate wood rot in untreated lumbers, including cedar and redwood. In addition, repeated water soakings lead to excessive shrink and swell cycles that result in cracking, cupping and twisting. For all these reasons, it is necessary to quickly seal any wood product that will be exposed to outdoor elements.
Before sealing new wood, it really pays to clean it, according to independent lab tests. Sealers can penetrate up to 25 percent deeper into new wood that has been cleaned with an oxygen bleach solution, the tests showed. The cleaning action opens the wood pores of the freshly milled lumber.
Oxygen bleach is a unique product. It does not remove the natural color from wood. What’s more, it is nontoxic to plants that surround your wood deck. It also does not harm wood fibers. It is safe to use oxygen bleach on all woods except redwood. Use oxalic acid to clean redwood.
Existing wood decks have to be deep-cleaned before they are sealed.
Often I have been told by salespeople to use chlorine bleach to clean wood decks. Chlorine bleach (sodium hypochlorite) is a fantastic sanitizing product if you want to kill germs. However, it creates havoc when used on wood.
Chlorine bleach removes natural wood color, destroys wood lignin (the glue that holds wood fibers together), can corrode metal deck fasteners and hardware, and can kill vegetation that surrounds decks.
Your disappointment with many wood deck sealing products is shared by many consumers and testing labs. Apparently many of the commonly available deck sealants contain wood-protecting resins made from natural products such as tung oil, vegetable oil, linseed oil and animal fat. These oils are gourmet foods for mildew and algae. To slow down mildew and algae growth, the sealers often contain toxic fungicides and mildewcides.
I have had fantastic luck with synthetic-penetrating water repellents. These products contain no food for mildew and algae. If you want maximum performance and protection, be sure to use a pigmented (colored) product, not a clear one. The pigment particles absorb and deflect UV rays, helping to protect the wood.
I have found that cooler weather, with daytime temperatures of 60 to 70 F, are best for cleaning and sealing decks. The cleaners do not evaporate quickly and the penetrating water repellents have adequate time to seep deeply into the wood before the sun can cause them to evaporate.
Avoid hot, windy summer days for deck cleaning and sealing. Reserve those for fun in the sun, not work.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352. Questions will be answered only in the column.
For a list of independent test results for 25 wood sealant products, manufacturers of synthetic sealants and oxygen bleach, and other tips on cleaning and sealing outdoor wood decks, send $2 and your name and address to Tim Carter at the above address. Ask for Builder Bulletin No. 217.
For a list of past Builder Bulletins and a wide variety of individual job bid sheets, send a business-size, stamped, self-addressed envelope to the same address.
Ask the Contractor can also be accessed via the Internet at http://www.chicago.tribune.com/homes/articles/askcon.
