Mold growth on decks or concrete surfaces can be a challenging problem to solve. Mold has the ability grow anywhere moisture is present and a food source for mold is available. Mold spores are microscopic so it is difficult to see them growing unless you have a magnifying glass or microscope as well as a trained eye for what mold looks like.
For information on your particular type of deck surface, try searching the internet for “mold-resistant” [product name] to find out if that material can help protect against mold growth. Alternatively, you could test one small area with distilled vinegar which will kill most types of mold within 2 hours if applied directly onto the affected area (see below). If no signs of mold growth appear after 3 more days, the area is probably not contaminated with mold.
If you already have a surface that allows for mold to grow, it’s best to prevent mold growth from occurring by minimizing or eliminating any possible source of mildew-causing moisture. Below are some tips on how to do this:
Make sure all deck boards and trim are sealed tightly so no water seeps underneath them into the wood itself where it can cause damage and eventually lead to mold growth.
Examine all caulking around your deck annually during fall/winter months when temperatures are cooler and less likely to condensation issues occur. Replace or repair any caulking that is cracked, peeling, missing, deteriorated or has become discolored (typically brownish in color).
Be especially careful to examine caulking around the perimeter of your deck and any area that gets lots of water runoff from rain or snow melting off your roof. Always wash down/clean up any leaves, dirt or other debris which may have accumulated on your deck in a timely fashion so they do not rot and become a food source for mold. Water left standing on decks can also lead to mildew/mold growth so it’s best to keep things dry whenever possible.
If you live in an area with high humidity levels during hot summer months, think about installing a whole-house ventilation fan as this will help bring more fresh outside air into your home (as opposed to moist inside air). In addition, you could open windows and doors throughout the house while the fan is on to further promote air circulation.
Always try to keep your house well-ventilated in general, especially during winter months when you’re not able to open windows as much because of cold weather and high energy costs. If installing a ventilation fan is not possible or if outside humidity levels are still too high despite the use of a whole-house fan, have door & window screens installed on all windows (if this hasn’t been done already).
Take 1/2 cup of distilled white vinegar and pour into spray bottle that has been filled with water until no air remains inside the bottle (do not use tap water). Spray solution onto affected areas until wet but not dripping wet. Let solution sit on affected area for at least 10 minutes before you wipe clean with a lint-free rag/towel.