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October 2 - October 8, 2016

What are the alternatives for removing mildew from uncoated concrete block exteriors before coating?


Selected Answers

From Zenith Czora of Parex Davco on January 3, 2017:
Depending on the severity of mold growth, look for a mold- and algae-killer which contains the active ingredients disodium octaborate trihydrate and benzyl ammonium chloride. Follow the instructions on how to use these materials. To prevent recurrence of mold and algae growth, it is best  to treat the now clean, mold/algae-free and dry, treated surface with a water-repelling and consolidating primer based on silicone and siloxane and topcoated with coatings which contain a  mold/algae inhibitor.

From Zenith Czora of Parex Davco on October 11, 2016:
 Test to distinguish mildew from dirt by applying a few drops of household bleach to the discolored area; if it disappears, it is probably mildew. Treat the mildew by applying a mixture of water and bleach, 3:1, and leave on for 20 minutes, applying more as it dries. Wear goggles and rubber gloves. Then scrub and rinse the area. Then, to prevent recurrence, treat it with an appropriate biocide.

From Hans Mugler of Mug Pub Inc on October 6, 2016:
I'm not nearly the professional that Timothy and Cameron are, just a lowly Publisher in the paint & sundries industry; but both my company and I have had great success removing and preventing the return of mold & mildew on exterior surfaces from concrete block to vinyl siding to wood decks and plastic fencing using the three-step approach and the family of products from Moldex Corp! Their products don't require a pressure washer, hazmat clothing or anything else but a hose to connect to the bottle. Safe products that do a terrific job with eliminating mold and mildew issues!

From Timothy Knell of Shore Corporation on October 5, 2016:
We recommend using a strong, alkaline cleaner for cleaning organic soiling and dirt from concrete block. If the surface is heavily contaminated, add some dilute bleach. The surfactants and alkalis denature the proteins and polysaccharides the microbes use to adhere to the concrete and each other. Pressure wash and dry. If using lots of water for rinsing is not an option, use a hydrogen peroxide-based cleaner. The gentle effervescence of the oxygen being released physically lifts the soil particles out of the pores and to the surface for easy removal. As most of the cleaner decomposes during use, there is little potential to leave residues that could affect the coating performance.

From Cameron Duncan of M-NCPPC on October 4, 2016:
For light colonization, use a diluted bleach solution to remove surface discoloration, followed by drying for 24 hours+ and vacuuming  the face of the CMU to extract dead and remaining fungi. Heavy colonization requires power-washing with full hazmat protocols, including specialized fungicidal mixes, application methods, drying, clean-up, everything.

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Tagged categories: Concrete masonry units (CMU); Mold/mildew-resistant coatings; Rehabilitation/Repair; Renovation; Repair materials; Surface preparation


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