A: Jim Grant, the owner of San Diego Power Wash in California responds: The most common problem I see in wood-deck refinishing is improper surface preparation. Many would-be deck refinishers don't realize that the surface you see before coating with a finish is the surface you'll see through the finish, so coating a discolored surface will result in an unsightly finished project.
Surface preparation begins with determining whether the deck already has a coating on it. If it does, you must decide whether you are going to simply clean the deck and reapply a finish, or remove the coating and start with fresh, clean wood. Look for obvious signs of finish deterioration, such as scuff marks, worn coating, areas void of any finish, areas that don't bead water, and traffic patterns from excessive foot, child, or pet activity. Examine the deck closely for mildew, mold, tannin stains, environmental fallout like soot or tree sap, and discoloration from chemicals such as pool products. All of these will show through a new finish, and their presence often indicates the need to strip the old finish. Also, if a coating scrapes away easily, it's probably best to take it all off and start fresh.
It's less expensive to recoat a deck before it gets to a state where the prior coating must be completely removed. If the existing finish is in decent shape, you can just recoat after using a wood brightener. I prefer brighteners that contain oxalic acid. After applying the brightener, following up with a pressure wash or brush scrubbing should leave the deck ready to be coated.
When you do have to remove an existing coating, there are several products to choose from. Strippers are designed for intact coatings or those that have been applied within a few months. I like strippers that contain sodium hydroxide, although they require careful use. Sodium hydroxide is also known as "caustic" or "lye" and can cause serious chemical burns to skin and eyes.
Wood cleaners are a softer, gentler version of strippers. I look for ones containing sodium metasilicate or sodium percarbonate. Though not as potent as strippers, cleaners still require careful use.
After you apply the cleaner or stripper (both of which slightly discolor wood), you'll need to use a wood brightener, followed by a thorough water rinse. Be sure to follow the manufacturer's directions exactly. Any products you use on wood surfaces should be applied evenly, which can be a challenge on vertical parts, such as railings. Be sure your rinse completely removes any strippers, cleaners, and brighteners from the surface, as they can interfere with the penetration of new coatings.
Minor sanding and resetting of nails and screws are standard on any project; sometimes major repairs are needed as well. I take care of these things after the deck has been stripped or cleaned and just prior to refinishing.
A poorly wielded pressure washer can do more harm than good. Always use the lowest pressure that will do the job.
Many contractors lack the experience or the knowledge to choose a reliable exterior finish. I was one of them. When I went into business, I was sold on a product by a fancy-talking salesman. I had coated 45,000 square feet of decking with his product when I started to get callbacks. The coating was failing after three or four months, though I had been told - and had told the customers - to expect it to last for three to four years. It turned out the local distributor had lied about the results of testing done on this product. I received a cash settlement of a dime on the dollar from the distributor and manufacturer, and I recoated all the decks at my cost. This almost cost me my business.
In order to have full trust and confidence in a product, a contractor must invest time in testing it and researching the companies that make and distribute it. Working with a manufacturer that has a solid history with exterior coatings and a proven track record of customer support is a good place to start. Even so, I've tested 50 products in the past 20 years. I test them on horizontal and vertical surfaces - on decking, fencing, and siding - as well as on different woods, including redwood, cedar, ipe, and mangaris. The only way to really know how a product will hold up in your climate is to try it out on your own test boards. Test finishes on whatever material you intend to refinish.
Contractors and homeowners need to understand the differences between coatings. Solid-body stains work well for a painted look on badly weathered wood. Newer formulations even hold up underfoot on decking. Transparent or semi-transparent coatings allow the grain and color of the wood to show through while still offering protection from both water and sunlight. Clear coatings protect the wood from water, but allow it to age slowly and naturally.
I've had success with Superdeck finishes (Duckback Products; 800/825-5382, superdeck.com). Penofin (Performance Coatings; 800/736-6346, penofin.com) also has a good product line, as does Wolman (Rust-Oleum; 800/323-3584, wolman.comvbvddzfsecrx). If the existing coating held up well and has not darkened or discolored, and the homeowner was pleased with its life span, then after doing a proper cleaning, you can reapply the same coating. That way, it's unlikely there will be any compatibility issues between the old finish and the new one. If you don't know what coating was applied in the past, however, it's best to strip the deck before refinishing.
Hiring the Inexperienced
Cleaning and sealing a deck involves more than just renting a pressure washer and rolling on finish. I stress to my new clients that it's not prudent to hire someone to do practice work on their deck. Bad pressure washing has ruined many decks by tearing out the softwood between the growth rings. Additionally, a pressure washer in inexperienced hands can tear screens, shred the leaves of plants, and blast water under thresholds and into cracks in window frames. In the worst case, a poorly aimed high-pressure water spray can peel back layers of flesh.
If you want to add a deck cleaning and refinishing component to your business, experiment with a pressure washer and a variety of strippers and cleaners before selling your service. Practice, practice, practice - there's no substitute for hands-on experience. Always use the lowest pressure that will do the job. Finally, be aware that in many parts of the country you are required by law to catch all your water and dispose of it safely.