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Outdoor wood will rot and crack from water damage if not treated periodically

By Tim Carter,

My outdoor wood furniture has weathered to a mottled gray, and there is mildew covering it. My wife has informed me that I must make it look like new. If I do a good enough job, I’ve been told I can then refinish the kid’s play set. What’s the best way to get the wood looking like new? How should I clean it? What’s the best sealer to use? If you were doing this job, what secret tips can you offer to get the best results in the shortest amount of time?

— Steve P., Manassas

It’s just as important to keep your better half happy as it is to clean and protect outdoor wood furniture. I urge you to maintain a positive attitude throughout this entire project. I’ve been married nearly 38 years to the same wonderful woman and have discovered that keeping her happy by completing projects is some of the glue that holds marriages together.

Cleaning and sealing any outdoor wood is not much different from doing the same thing for a wood deck. Outdoor wood tables, chairs, fencing, wood play sets, arbors and so forth all take the same abuse from Mother Nature.

If you fail to maintain outdoor wood, it will eventually rot and crack to pieces. Chemically treated lumber is able to resist rot for decades. Some wood, including redwood, cedar and teak, contains varying degrees of natural wood preservatives. But water that soaks into any of these wood species will cause them to crack.

The cracks start out as tiny checking cracks. Water entering the wood causes it to expand. As it dries, it contracts. This movement creates the tiny cracks. If water gets into the cracks, it soaks deeper into the wood, causing even greater expansion and contraction forces that cause the cracks to get deeper and wider.

You can see why it’s important to treat all wood with a water repellent on a regular basis. Do this every other year or so and your outdoor furniture and play set will look fantastic instead of resembling a 50-year-old fishing pier.

I prefer to clean outdoor wood with oxygen bleach. However, do not use oxygen bleach on redwood, as it can darken this wood species. Use oxalic acid to clean redwood.

Do not use a pressure washer to clean outdoor wood. It absolutely will damage the wood. The high-pressure stream of water erodes the softer, lighter-colored bands of spring wood that are found between the darker bands of summer wood grain.

Allow the wood to dry well after it’s clean. The washing process almost always raises the grain of the wood. This means you’ll have to sand it to get it back to that smooth furniture finish. Don’t skip this important step. A palm sander works great for this project. Use a medium aluminum oxide sandpaper. This paper sharpens itself as it’s being used.

Once the wood is sanded, you should seal it with a pigmented synthetic resin water repellent. Do not use an oil-based product. Most oil-based sealers are food for mildew and algae. The manufacturers place mildew-cides and algicides in the products to slow down the growth, but water and sun break down these chemicals. The pigmented or colored sealers will keep the furniture looking spectacular. Clear sealers will gray rapidly.

I urge you to work in the shade when applying the sealers. Some sealers require you to apply two coats within 15 minutes of each other to get maximum protection. Working in direct sunlight can shorten this time dramatically, leading to ugly spotting and overlaps.

Working in the shade is easier on you, the wood and the sealer. If you can move the furniture inside your garage or other covered work area, do so. I realize this is impossible for the play set, so choose to work on an overcast day if possible.

Tim Carter is a columnist for Tribune Media Services. He can be contacted through his Web site, askthebuilder.com.

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