How to Treat Wood to Resist Rotting

Wood exposed outdoors can last for centuries, But how? What kind of wood you choose and how you protect it makes a big difference in how long the wood lasts. Two conditions influence the service life of outdoor wood: weathering and decay.

Weathering is breakdown from the elements such as the sun, wind, debris, and moisture. If wood is not protected by paint or stain, the weathering process removes about ¼ inch of wood per century from softwoods on vertical exposures; even more wood is eroded in severe exposures.

But that's not the worst of it. Sun exposure is an even larger problem that will accelerate the decay and rot process by allowing moisture and insects to invade the unprotected regions of the wood. One way to reduce the likelihood of decay is to use treated wood. However, treated wood is often green or has other potentially undesirable properties, such as a tendency to warp.

To prevent weathering you must block the sunlight. Finishes differ in their ability to protect wood from the sun. Paints can block sunlight completely, but they can trap moisture and encourage decay. Semitransparent stains are the next best way to block sunlight, followed by water-repellent preservatives, especially those that contain ultraviolet light inhibitors.

Heartwood is a good wood because it comes from the center of the tree where the wood is most compact and dense. There is consensus that some second-growth timber, even from a decay-resistant species, is not as durable as the old-growth timber. The durability of any wood decreases as rain or other sources of moisture remove the natural preservatives. Wood kept dry will not decay, although it may still be vulnerable to attack by insects.

Rot and decay resistant woods such as cedar and cypruss are ideal, but even they have a tendency to crack if not kiln dried or protected with a strong finish. Treated woods also need to be finished to reduce the ability to weather, delaminate, and become unprotected. The penetrating finishes (stains and water-repellent preservatives) that are used on wooden decks can also be used for all wood discussed here. The best way to protect outside wood from weathering is to cover it with a roof. A roof also prevents decay as long as there is no other source of moisture, such as contact with the ground.

Contraction and expansion from sunlight exposure is the other problem that can open up the wood and cause it to twist, separate, and rot quicker. Avoid the use of dark paint colors if possible that will cause more absorption and problems from the sun.

Taking care of exposed outdoor wood may be tedious, but we have the proper instructions to keep you and your precious goods in great shape.

Outdoor furniture requires a durable finish that does not rub off on clothes. Paint can serve this purpose. Enamel paint provides a hard surface that wears well. Thin the paint for the first coat to increase penetration. A light sanding is desired to help rough up the surface for better paint adhesion and longer lasting paint. This will keep the paint from fading as quickly. If possible, paint the end grain before furniture parts are reassembled.

Fences probably have the most finishing options. Acrylic latex paints are better than oil-based paints, unless the fence is likely to be used for sitting. Highly colored woods such as redwood and cedar require a stain-blocking primer. Pretreating the wood, especially the ends, with a paintable water-repellent preservative (WRP) will increase the life of the paint.

So what tricks can you use to make your finish last years longer? Subject the wood to one or two wetting/drying cycles before you apply the finish; wet the wood (e.g., with a hose) and let it dry completely each time. Sand the wood before applying the finish, and apply paint to wood soon after that. And boom... you will help prolong the life of wood...