A diluted solution of soap and water with a stiff brush will remove mildew and dirt.
Wash away the dirt with a hose or a very low setting (below 500 psi) on a pressure washer. The impact of water above a 500 psi setting on a pressure washer, as well as bleaches and oxidizers, can damage the wood fibers and are not recommended for deck cleaning.
For tougher stains, use Oxalic acid-based (sometimes sold as wood bleach) deck cleaners.
Never use household bleach or foaming cleaners as they can strip the preservatives and damage the wood fibers leaving an unnatural whitewashed appearance.
We recommend that the use of a pressure washer be limited to only the highly-experienced and/or professionals. Improper use can damage the wood surface and fibers. If you choose to use a power washer, use the lowest possible pressure setting (keep it under 500 psi) and fan tip only approximately 18 inches from the deck.
Mold that you find on pressure treated wood is not an indication of a fungal attack. Mold can grow on the surface of many products including wood (treated and untreated) due to exposure to moisture. To remove mold from your treated deck, use mild soap and water solution and a stiff brush.
Mold and mildew are present everywhere in our environment, both indoors and outdoors. Mold and mildew need four things to thrive: air, water, temperatures between 32 and 120°F, and a food source, conditions that are common wherever humans live, work, and play.
The best way to minimize mold and mildew growth is to control water and food sources. When it comes to mold or mildew on wood decking, water and organic matter are the primary conditions that enable mold and mildew colonies to thrive. To minimize these conditions, make sure water has the ability to flow away from the deck surface and areas surrounding the deck to lessen the absorption of water. Ensure there is adequate ventilation between deck boards and underneath the deck surface, so water can rapidly evaporate.
And since both mold and mildew feed on dead or decaying organic matter, so it is important to keep your deck clean of leaves and debris.
Cleaning Your Deck
To minimize mold on your decking, clean your deck as often as needed, at least twice each year. Climate conditions vary in different regions of the country and may necessitate more periodic cleaning.
Remove leaves, debris, and other organic materials that provide a food source for mold.
If mold is present, there are many commercial products available for cleaning mold. We recommend commercial cleaners containing oxalic acid. For best results, follow the manufacturer’s instructions and use cleaners within their stated shelf life. Do not mix recommended cleaning products together as harmful chemical reactions could occur. To maximize application coverage, remove excessive organic growth or clumps prior to applying the cleaner.
Coatings for High Mold-Prone Environments
For environments prone to high mold growth, there are commercially available coatings and finishes that seal the wood surface when applied and they should be maintained per the manufacturer’s instructions.
Coatings should be applied within one week of cleaning for best results.
Prior to coating, properly clean the decking, rinse thoroughly with water and hose and allow to dry completely.
Sweep off any pollen and debris.
Tips for Minimizing Mold
Maintain a deck that is dry and clean.
Ensure gutters / down-spouts and dryer vents do not discharge directly on decks.
Ensure adequate ventilation under and between decking boards.
Minimize water puddles under decks and the use of wet mulch up against the deck structure.
Cleaning a deck just after the last of the major pollen events (when your car doesn't change color from the pollen anymore) will minimize the seasonal outbreak of mold and mildew.
Periodically rinse off your deck using a garden hose with a spray nozzle, especially after the major pollen events. Skilled professionals may use pressure washers with wide fan tips but in the wrong hands, your deck can be damaged. Exercise extreme caution when using pressure washers.
Ensure the gaps between the decking boards remain free of debris so that regular rain showers can remove pollen and organic debris between cleanings.
Preserve CA is copper azole and contains 100% recycled copper and is available in ground contact or above ground applications depending on the preservative retention level in the wood. Check the end tag for proper use.
The Preserve CA-C, Copper Azole Type C preservative formulation is made of 96.1 % soluble copper and organic triazole co-biocides; tebuconazole and propiconazole, which help control copper-tolerant fungi. Preserve CA-C is widely used across the USA.
The Preserve CA-B, Copper Azole Type B formulation is very similar, also made of 96.1% soluble copper and 3.7% tebuconazole. Preserve CA-C has been registered for use in Canada since 2002.
ACQ is alkaline copper quaternary. Viance introduced this arsenic-free, water-based preservative in 1992, which replaced CCA when it was phased out for residential use in 2004. Preserve ACQ contains 100% recycled copper.
In 2020, the quaternary used in ACQ was diverted for use in healthcare products due to the Covid-19 pandemic. All treaters have now switched to CA.
Designwood is a premium, long-lasting colorant that can be added to Preserve CA to infuse color throughout the wood. This provides a finished project from the start with no need to initially stain. Saves a lot of time and money especially for decking, stairs, railing and balusters, bridges and fencing.
TimberSaver is a water-borne borate treatment or DOT (disoldium octaborate tetrahydrate). Lower in toxicity, TimberSaver is used for interior treatments for sill plates, framing, furring strips, trusses, joists and sheathing, especially in areas of high termite risk.
Moldex® 45 Mildewcide is an isothiazolinone compound for the temporary control of mold and mildew control treated wood building products. Moldex 45 is environmentally friendly and does not persist in the environment.
Moldex® 45 at a concentration in the range 220 ppm to 250 ppm of active ingredient is recommended for the control of mold in copper-azole (Viance CA-B,CA-C, and Pack PT) treating solutions.
Stable Formulation containing:
2-n-octyl-4-isothiazolin-3-one (45% by weight)
Appearance: Clear to slightly hazy liquid
Odor: Mild Specific gravity (20°C) 1.034
pH: (as supplied) 2.4
Viscosity: 40 cP
The active ingredient is not changed by short-term temperature stress during processing at up to 60°C. However, the product stability is affected by alkalinity and oxidizing agents in the treatment solution.
For best results, the treatment solution should be maintained at a pH of 8 or below; and the active level of MoldEX® 45 monitored and formulated as required to maintain the desired concentration.
Many factors such as temperature, air circulation, depth of penetration, moisture content, mildew and mold can affect the performance of the treatment. Therefore, the protection period can vary. Testing and experience from our technical experts will help you determine the solution for your treatment.