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Removing mold and re-waterproofing Sunforger canvas on a Yurt


Heather Leach asked:

I live in a yurt with Sunforger canvas side walls. This summer has been terribly wet and the yurt walls have mildew and mold growth. I was wondering if I could get a sample of the fabric kleen and canvas shield to see if they will work for me. I am hesitant to buy it outright because I bought another canvas cleaner and it took the waterproofing off of the canvas.


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Sunforger canvas is a tightly woven cotton canvas that has been dipped in a silicone fluid bath to give it waterproofing. This is different from marine canvas which is mostly synthetic, either acrylic or polyester fabrics, and most have been treated during manufacture with PTFE applied at elevated temperatures to give it waterproofing. The PTFE coatings are more durable and resist attack by oily pollutants as well, but unfortunately is also a carcinogen. Silicone treatments are more susceptible to removal by washing and if there is an oily material, such as unburned jet fuel or automobile exhaust pollution. from atmospheric fallout, that lands on the surface it will compromise the waterproofing ability of the silicone coating.Any heavy duty cleaning, such as to remove mold can also remove the waterproofing and your fabric will need to be re-waterproofed.

Once mold incubates and starts to grow on the surface, it can also penetrate into the substrate and will feed on some silicones. Removing the mold will also necessitate removing the silicone waterproofing.

Our system matched products; Fabri-Klean and Canvas Shield were developed primarily for marine fabrics and for the marine environment, which as you know is the toughest on the planet. During the development of these products however, we also tested on other fabrics such as cotton, wool, silk and even tissue paper with remarkable results. We found that Fabri-Klean, with its deep penetrating power and free rinsing abilities was superior to all other soaps and cleaners that we tested and Canvas Shield provided superior waterproofing, durability and UV protection, to other brands and types. Although our testing was extensive, we were unable to test all fabrics. We did find that the tightness of the weave to be important. It was difficult to waterproof loose weaved products.

There is a great misconception about the difference between mold and mildew and most people use the names interchangeably. It’s unlikely that you have mildew on your canvas. Mildew is whitish in color and only grows on living plants. Mold is darker in color and can be brown, black, pink or green, depending on the species, of which there are many thousands. Mold grows on dead or decaying material or soil and requires mold spores, which are everywhere, warmth, moisture and shade to incubate. If left unchecked, it can penetrate into the substrate and cause permanent damage and indelible staining. Mold can also negatively affect the waterproofing of fabrics by acting as a wick to carry the moisture through the threads.

We have not done any tests or experiments using Fabri-Klean or Canvas Shield on Sunforger cotton duct, but based on our tests with other fabrics I suspect that both products will work well for your application. Because of our lack of testing, I can only make suggestions and stress that you do your own testing on an inconspicuous area to make sure that you’re getting the results that you want before treating the entire yurt.

We don’t have samples but we do sell our products with a 100% customer satisfaction or your money back guarantee so you can order a kit or small amount of product and try it on your test area. When you’re happy with the results you can order more for the entire yurt. If it doesn’t work for you, you can return the unused portion and get a full refund of you purchase price.

The first order of business is to get the fabric clean and free of mold. As you know, mold can be hazardous to your health so this is important. To clean the canvas, wet it with water, spray on Fabri-Klean and scrub it well with a scrub brush, on both sides, and then rinse clean. Fabri-Klean is free rinsing and will not leave soap scum behind to affect the waterproofing treatment to follow or be food for mold, but it will remove the existing waterproofing. If you plan to do the cleaning while the canvas is stretched on the wooden frame, test first to make sure that the wood does bleed and stain the fabric.

If the mold has been on for a while and is not removed with Fabri-Klean then you can try a solution of one gallon of water, one cup of chlorine bleach and one cup of Fabri-Klean. (Test first). Wet the fabric thoroughly with the solution, scrub and let it work for about 15 minutes, scrub again and rinse thoroughly. This works on synthetic fabrics but we don’t know if it is injurious to your fabric, especially if it’s colored. Sunforger fabrics are made in China or India and we don’t know the quality. If it does not get all of the stains out, then they’re indelible and you won’t be able to get them out.

Once the canvas is clean and dry, you can then waterproof it with Canvas Shield. Canvas Shield uses Drykon, a new Nanoized Polymer, instead of silicone which does not work well on marine canvas, or PTFE which emits PFOA as it ages and breaks down, and is a carcinogen. Canvas Shield allows the fabric to breath, which is important, and is easy to apply. For the large area that you are treating, I recommend putting it into a garden sprayer and spraying the outside of the fabric until it is evenly wet. Wait for it to dry and apply a 2nd coat and let that dry for a minimum of 24 hours, avoiding contact with rain or water. It’s best to apply Canvas Shield when the weather is dry, warm and sunny. The warmer the better. Be sure to keep it dry during the application and cure time.

Canvas Shield with Drykon will give your fabric superior UV protection and resist mold better than your current waterproofing. If mold is a constant problem, you can also treat the inside of the fabric which can help, but normally this isn’t necessary. The best way to prevent mold is to keep the fabric clean and dry.

You can also use Canvas Shield on upholstery, cushions, outdoor patio furniture fabrics, canvas awnings, even mattresses. Be sure that the fabric is clean, dry and free of soap scum or residue before application.

Thanks for your question,

Captain Aurora
Richard Kittar

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