Wood decks are never supposed to be finished with a "Film-Forming" finish. That advice, and the rest, is from the USDA Forest Products Laboratory (www.FPL.FS.FED.US) so it is scientifically proven, and the FPL has been around for 100 years. Sunlight makes any wood surface erode. Therefore any coating applied to a wood surface, like your deck, that is constantly exposed to sunlight, will need to be constantly reapplied. Even penetrating oil stains have the problem because the oil penetrates but any coloring pigments do not. The pigments cling only to the surface fibers, which are constantly departing due to the sunlight damage (photochemical degradation). Incidentally the photochemical response to the lignin in wood being damaged by sunlight is universal, it turns color. It Turns Grey. Now you know why all wood turns grey in the sun. The wood fibers in plastic wood composite usually have the same reaction, only because they aren't wood, the WPC materials like trex end up looking more like concrete. Wood makes a better deck because it doesn't hold the summer heat. Wood is an insulator, especially softwoods like cedar. Wood is also resilient so it springs back when you step on it, it is not dead like concrete or WPC. Makes standing on wood far more comfortable than concrete or WPC decking. The other thing is the plastic soften and bend over the joists over time, especially in hot climates. Wood has its own strength and doesn't do that.
Use a clear finish and it wears off the fastest because it has the least ability to resist sunlight. Semi-transparents last longer because they have pigments to offset some sunlight damage. Cleaning wood is done without a power washer, which will turn a smooth wood deck into one with grain raise and often a torn stringy surface in need of sanding. Wash the dirt and mildew by using some oxiclean or if the deck is fairly clean, some powered laundry (Tide with Bleach) detergent. Brush the surface with the solution, let it sit (do it on an overcast day)for 15 minutes, brush it again (i use soft push broom ) then rinse it well. The deck is now clean. Stains can be removed with wood brightener read the label, you want Oxalic Acid, NOT sodium Percarbonate ( that's what's in the oxi-clean). 3ounces in 1 gallon warm water (careful it'sPoison to people and pets) will remove any stains, then rinse again. When dry refinish the deck. Oil stains -NEVER apply more than 1 Coat, they will prevent mildew only when they dry completely. Two coats become "Miracle Grow for Mold & Mildew" because they stay wet and oily.
Clean wood decks in cool weather for best results never in hot mid-summer sun, which actually causes damage to the wood.
