DEAR TIM: 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 past sealers. Is there one that resists mildew and algae? What is the best weather to clean and seal decks? Larry C., Apple Valley, CA

DEAR LARRY: I have had the same thing happen to me. 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, there is a considerable amount of 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 immediately attacked as soon as it is exposed to the sun's ultraviolet (UV) rays and 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. This water can accelerate wood rot in untreated lumbers such as cedar and redwood. In addition, repeated water soakings lead to excessive shrink and swell cycles that result in cracking, cupping, and twisting. For these reasons, it is necessary for you to quickly seal any wood product that is exposed to outdoor elements.

Independent lab tests have shown that it really pays to clean new wood before it is sealed. The lab results indicate that sealers can penetrate up to 25 percent deeper into new wood that has been cleaned with an oxygen bleach solution. 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 non-toxic 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. I have successfully used oxygen bleach on redwood, but in certain instances it has been known to darken it. If you want to be completely safe, 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 the fantastic luck with synthetic penetrating water repellents. Look for ones that are formulated using synthetic oils and resins. 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 product. The pigment particles absorb and deflect UV rays helping to protect the wood.

I have found that cooler weather with daytime temperatures of 60 - 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 evaporate them. Avoid hot, windy summer days for deck cleaning and sealing. Reserve those for fun in the sun, not work!

Message from Tim: Years ago while researching a column about cleaning decks, I discovered the wonders of Oxygen Bleach. It is perhaps the 'greenest' cleaner I know of as it uses oxygen ions to break apart stains, dirt and odor molecules. There are no harsh chemicals, and it works on just about anything that is water washable. I decided to create my own special blend using ingredients made in the USA. In fact, the raw materials in the active ingredient are food-grade quality registered with the FDA. I call my product Stain Solver. I urge you to use it to help clean your deck surfaces. You will be amazed at the results!

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Comments: Welcome! I, Tim Carter, don't answer questions here. If you post a question here in the Comments Area, perhaps another visitor will help you. You need to go to the Ask Tim page if you want a question answered. Once there, look closely at how many weeks behind we are. Please be patient as you use this free service. If you have an emergency and need to talk to me, there is an option there for you. J D Whipple 01 Jan 2008, 16:24 Hi, We've had our deck for 9 months, but it was never sealed. We've had our share of splinters, and a couple of warped boards, but have questions about winter months care (if any) before we can seal it in the spring. Plus, If need to sand, of fill the splinters, Just trying to save the deck this winter until we can seal it right.. AsktheBuilder 01 Jan 2008, 17:10 JD, I would just read all of my Deck Maintenance columns and see what is possible given your location. Derek 19 Feb 2008, 14:30 would 100% orange oil be a good redwood pergola praservative? ie bugs, sun, weather.... AsktheBuilder 26 Feb 2008, 20:31 Derek, I doubt it. This sounds like an algae and mold buffet item....... You need to read all of my Deck Maintenance columns. Paul Murray 05 Apr 2008, 19:31 Tim, last summer I cleaned a new deck with your Stainsolver product and then stained the deck with Defy for cedar. I now am seeing some areas where the Defy is coming off. I'm here in Oregon where we've had a wet and cold winter. Is it likely that I did not do a good enough job of removing mill glaze on the new cedar decking? What is the correct way to resolve this problem at this point? More Stainsolver on the affected bds and reapply the Defy product? The Defy has not come of completely so I'm concerned about how to get the right match with the rest of the deck once I reapply the stain. AsktheBuilder 09 Apr 2008, 17:09 Paul, You need to speak with the Defy people since the issue is with the sealer. Cedar is one of the toughest woods to seal because the summer grain of the wood is so dense the sealer can't penetrate. Cindy 06 Jun 2008, 18:44 Can I apply a water repellant/sealant in temps of 90+ degrees? Charley Mason 23 Jul 2008, 11:29 I'm looking for a commercial grade stain/sealant for my redwood deck. I live in Arizona. Moisture isn't the problem, heat and UV deterioration is. Any suggestions? Thanks, Charley      View all comments *Name: Email: Notify me about new comments on this page Hide my email *Text: Security Image: Security Image Text:   Remember, Tim Carter doesn't answer questions here in the comments. You need to go to the Ask Tim page.