How to Clean Wood Deck Mildew

Painting the deck is a great do it yourself project that gives any home an immediate exterior facelift. But before you break out the brushes and paint a deck, you have to do the appropriate prep work. One of the most important things you need to do before you begin painting is eliminate any mildew that may be present in the deck. Mildew is a fungus that can grow on just about any surface, particularly thriving in moist and dark areas. If left untouched when you paint your deck, mildew poses both aesthetic and structural problems. Aesthetically, mildew attracts dirt and lessens the adhesion of paint to the wood, resulting in a flaked, blistered, or cracked paint job. Structurally, mildew weakens wood because it feeds on wood cellulose and resin. You obviously want to avoid both of these problems, so it’s important to know how to clean wood deck mildew before you begin your deck painting project.

wood-deck-mildewIt’s easiest to clean wood deck mildew on a hot, dry, and sunny day because the natural outdoor conditions will give you an assist in drying out the wood to create an inhospitable environment for mildew. Heat also kills mildew spores, helping you protect against new mildew growth. The most effective method for how to clean wood deck mildew is a chemical cleanser designed to kill the fungus. Before you start using chemicals on the deck, however, you should thoroughly rinse it with pressurized water. Use a power washer or a hose with a pressure nozzle to systematically wash the wood surface of the desk.

Once the deck is thoroughly pressure rinsed, it’s time to get to work a mildew-killing solution. You can purchase a commercial mildew cleaner or mix one of your own. To make a homemade wood deck mildew cleanser, mix three quarts water, one quart oxygen bleach, and a quarter cup of ammonia-free liquid dishwasher detergent. Whether you are going commercial or do-it-yourself with the solution, make sure to wear gloves and a mask to protect your skin and lungs from the chemicals. Spray the wood with the solution and allow it to sit for ten to fifteen minutes. After you have let the solution sit long enough to kill the mildew, thoroughly rinse the deck with pressurized water again. If you have any particularly stubborn areas with mildew, you may need to repeat this step. If it still doesn’t seem like it’s working after that, it’s probably time to seek some professional guidance about how to clean wood deck mildew.

Assuming that you successfully remove the mildew, however, the next step is to protect the wood against future mildew growth. First, sand the surface of the deck to prepare it. Next, paint over the wood with an oil-based deck sealant. This sealant will repel water, making it less likely that wood deck mildew will be able to take hold in the future. Once this step is complete, your newly mildew-free deck is ready for painting.


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