Any wood left exposed to the outdoor elements will cup, crack, and warp within the first year or so if it is not protected. Nature's job is to break down all materials that are no longer alive - and that includes the lumber used to build your deck or fence. The two natural enemies of wood are sun and rain. Sun breaks down the surface fibers, causing the wood to weaken and turn gray during the process. Rain causes the wood to swell excessively, eventually leading to breakdown of the internal fibers. Once this happens, the wood becomes spongy and weak. Even the daily cycle of morning dew and afternoon sun causes the wood to swell and shrink, speeding up the deterioration process.
Obvious signs of trouble are:
- Grayed surface (sun, or UV damage)
- Warping and cracking (water damage)
- Loose nails (a sign of excessive swelling and shrinking)
Some homeowners think that pressure-treated wood needs no additional treatment, but this couldn't be farther from the truth. Pressure-treated wood, as well as cedar, cypress, and other exotic woods, may be immune to insects but are not immune to the damaging effects of weather. Wood that is not protected often becomes unsafe in as few as seven years. Regular cleaning and sealing extends the life of a deck or fence many times over. It saves trees, and saves you money over the long run.
When should this work be done?
An old half-truth that causes homeowners a lot of trouble is the advice to "wait a year or so for the wood to dry out" before sealing. A lot of damage occurs during this first year, and much of it is irreversible. While its true that wood must be completely dry to take on a sealer, this drying is often accomplished in as little as 6-8 weeks. The use of an electronic moisture meter by a trained professional will identify when new wood is dry enough to seal. Do-It-Yourselfers can test the wood dryness by sprinkling a few drops of water on a shaded surface of the wood. If the water is absorbed within moments, the wood is probably dry enough to seal.
The truth is that wood that is properly sealed within the first three months will last longer and look better than wood sealed after a year.
How do I get started?
Note: This discussion assumes that the wood has not previously been sealed.
Preparation of the wood before sealing is more important than any other phase of caring for decks and fences. Proper cleaning a) eliminates dirt, mildew, mold, and algae; b) opens the pores of the wood; and c) balances the pH of the wood so that the sealer bonds to each fiber.
Choosing the right cleaners is not as easy as you might think. For example, most deck and fence cleaners are either acidic or alkaline. The Do-It-Yourself market offers powdered cleaners that are relatively pH neutral and are reasonably safe to use. Many home improvement stores recommend acid-based cleaners because they are less dangerous than most alkalines for the average homeowner to handle. Unfortunately, they are also quite a bit less effective. Alkaline-based cleaners are less consumer-friendly but are a lot more effective. Experienced professionals spend a lot of time learning about cleaners and how to handle them, and that is a good part of why they are worth what they charge. The most successful professionals clean with an alkaline-based cleaner and then neutralize the cleaner with an acidic brightener. This two-step process allows the natural colors within the wood to "pop", making the deck look fantastic - even before sealing
You can find professional-grade cleaners at many industrial contractor supply stores. The products usually recommended by most hardware stores and home improvement chains just don't perform like the commercial-grade cleaners.
Blasting with high-pressure water will remove the gray from wood, but it will also damage the surface of the wood. The proper washing technique is to use light pressure, the right wood cleaners, and large amounts of water. Do-It-Yourselfers have to be careful here. Rented pressure washers and machines made for homeowner use are made to put out 1750 to 3500 PSI. This is fine for knocking off old paint and cleaning concrete, but this much pressure will always damage wood. Wood should be washed with pressures between 500 and 800 PSI. Experienced contractors who specialize in wood care have their wands or pressure-washers modified to work at these pressures.
Never use a hot-water pressure washer. The hot water will raise the grain severely.
Striping, which is the marking caused when someone starts or stops the cleaning stroke of the pressure washer wand too close to the surface of the wood, is another problem. A lot of striping marks will make the deck or fence look uneven and unprofessional. Homeowners should practice making an arc (a partial golf swing) with the wand before they start to clean the wood.
As a general rule, previously-sealed decks or fences usually need to be stripped before re-sealing. All retail (do-it-yourself) and many commercial sealers contain elements that should be removed before any new sealing is done. This involves using very strong chemical strippers, and is the sort of job best left to an experienced professional.
Selecting a sealer.
OK. Your deck is clean and bright and ready to seal. What sealer do you select? How much should you spend for a quality product?
There are three different categories or types of sealers available, with a possible fourth choice on the horizon. They are oil-based, wax-based, and acrylic, with a recent appearance by latex-based sealers. There are distinct characteristics to each.
Prices vary widely, but the old maxim is our best advice: "You get what you pay for." We will give you price ranges for every product class. If you select a product at the low end of the price range, you will probably be disappointed with the end results.
Wax-based sealers are commonly found at do-it-yourself stores and are the sealers most advertised on TV. They can afford to spend these advertising dollars because the products are so inexpensive to manufacture. Wax-based sealers have a relatively short lifespan, usually 6 - 8 months. When they fail, they usually turn a deck black. Wax-based sealers are easily identified because water "beads up" on them. Wax-based sealers clean up with soap and water. Wax-based sealers cost $12 - $15 dollars a gallon. In general, these sealers are a waste of time and money.
Oil-based sealers also clean up with soap and water, but are quite different than the wax-based ones. Oil-based sealers come in two types - those made with vegetable oils (linseed or tung oil, for example) and those derived from crude oil. The products derived from crude penetrate better and leave the wood with a soft, natural appearance. Products made with vegetable oils contain natural sugars and starches that can promote and/or support the growth of mildew, etc. They leave the wood with a sheen, and can even form a varnish on the surface. These linseed oil sealers can be very difficult to remove, and usually must be stripped before re-treating. Crude-based sealers generally do not need to be stripped before re-sealing. If properly cleaned, a new layer of a similar sealer can be applied over the old one when it is time to re-do the deck or fence. With oil-based sealers, rainwater sheets on the surface and evaporates. Oil-based sealers available from do-it-yourself stores usually contain some vegetable oils and generally last 12-18 months before renewing is needed. Commercial-grade oil sealers usually last 24 months or more before renewing is called for. These products cost $15 - $30 dollars per gallon, and vary widely in quality. The best feature about sealers made from crude oil is that they can be stripped easily and inexpensively, allowing you keep the wood looking beautiful and natural with the lowest initial investment.