Since the Environmental Protection Agency (EPA) started banning the use of pressure treated wood due to chromated copper arsenate (CCA), most people have decided to seal their wood decks as the EPA suggests to prevent the arsenic from leaching into the soil. Most homeowners use local companies to pressure wash their decks and siding to save valuable time and the expense of rental equipment and some prefer to do the job themselves on a hot summer day. If you decide to hire a contractor to perform the work for you, there are a lot of important questions you need to ask before you should allow them to work on your home. First, make sure the company your hiring has the experience and the right equipment to perform the job properly, using more than 1,000 PSI or less than 4gpm can cause damage to wood. In Maryland, your also required to have a Maryland Home Improvement License (MHIC) for sealing decks or any repairs and it must be listed in all advertising and vehicles.

Make sure that any contractor you hire has a copy of this license and a long history of performing work in the area also; check them out with The Better Business Bureau. Another way to protect yourself is to use a company with certifications and affiliations in their industry like The Power Washers of North America.

It will cost more time and money to find the right contractor for you but it could cost far more, to hire a company without the proper experience or to do the job yourself. For example, most people don't know that using household bleach to remove the mold and mildew from your deck will actually damage the woods lignin fibers. Or that too much pressure can also damage the woods surface and cause it to splinter or fur. To many companies have decided they could tackle it without the proper training and with most machines putting out an average of 3,000 PSI it can be dangerous to the operator and your property. Properly learning the techniques and training for cleaning wood takes time, training and a long-term investment, each deck or house is different and they all require special attention. First you have to find out if there is an existing sealer or stain on the deck and how to remove it properly. Very similar to painting, deck sealers and preservatives won't properly adhere to a wood surface that has an existing sealer on it. First this product must be removed from the deck using a stripping agent and you must take steps to ensure that the stripping agent will not harm the plants or siding on the home. Most deck stripping agents have a sodium hydroxide base that will remove the existing sealer or stain and then it can be washed off with a pressure washer using a maximum of 1,000 PSI. When using a pressure washer you must clean with the grain of the wood the entire length of the board. By varying your distance from the wood or not going with the grain you may cause marks and discoloration in the surface. If done carefully, this will leave you with a clean surface for the next step.
Now that you have used a deck stripper to remove the last sealer, the surface must be neutralized so the sealer will absorb and adhere to the wood. Wood and other surfaces can be neutralized using citric or oxalic acid to bring them to a neutral Ph level, Oxalic acid will also remove tannin or leaf stains and also those iron or rust stains from rusting furniture. Now your wood surface is ready to be sealed and there are many other options to consider. The various sealers can be confusing to some but it's important to use a product that has ultraviolet protection from the suns rays. Most sealers have some UV protection, various oils to moisturize the wood and mildew prevention to fight the growth of mildew and mold. The best UV protection can be found in sealers that contain a pigment or stain, almost all of these products form a film on the woods surface, that may wear off with foot traffic or pets, they are semi-transparent allowing the woods natural grain to show while adding a tint of color to the surface. They will also help blend the over all color of the wood if some of your lumber has a different shade than others. You can also use products with solid colors, which don't allow the natural wood grain to show through and in most cases they usually appear to be painted when completed. Then there are preservative-based deck sealers that will penetrate into the wood. These products come in clear and different stain colors and they tend to last the longer because they penetrate into the wood. This allows the oils in the sealer to penetrate into the wood, which keep the wood from dry rotting, cracking, and also blocks the suns UV rays. These preservative sealers will hold up twice as long as the surface film forming agents and they will extend the life of the wood.