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Thread: removing mildew from canvas

  1. #1
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    Default removing mildew from canvas

    My boat cover and sail cover have this black mildew in it in various places. I tried scrubbing it with Ajax in a small area but it made no difference. It looks like it's in there permanently. After the winter on the side of the boat that didn't get much sun to dry it out is the worst. Any ideas? It's starting to look ugly.

  2. #2
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    A bleach solution may work, but test it on a small section first.
    Pet photography, the degree you get when you fail aromatherapy - Duck D.

  3. #3
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    Bleach is the most logical approach. I have used it but followed up with a treatment of lots of rinsing other wise the canvas or stitching could end up damaged.
    JG

  4. #4
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    Before you use chlorine bleach:

    a) think about what a splash of bleach does to your denim jeans - Sunbrella is more durable and and the chlorine - especially if diluted - won't eat a hole in it, but chlorine products should be a last resort. And as Todd Bradshaw has said numerous time, re-treat the canvas with Scotch-Guard;

    b) try a couple of laundry stain products. Mildew is actually a growth, but I've had good results with Spray-n-Wash or similar product touted to remove grass stains;

    For future reference, the time to address mildew or algae is when you first notice it. I.e. a small area under the Bimini frame or a corner that doesn't get much sun is a lot easier to clean than the whole business. Nipping it in the bud (so to speak) also seems to go a long way toward halting further growth.

    Good luck with your project.

    - M

  5. #5
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    Hold on kids, Bon Ami is an abrasive and depending what form of Ajax you used, it may be as well. You're not trying to sand the mold off, so don't use it on canvas! You also don't want to treat Sunbrella with Scotch-Guard or anything else that uses silicone as it's major water repellent ingredient (like Rain-Ban or any number of other silicone sprays) . Use a fluorocarbon treatment like 303 Fabric Guard to re-treat the fabric instead. Silicone is not compatable with the factory finish on Sunbrella and may leave spots where the two treatments don't get along and the fabric is leaking. 303 is also better at renewing the UV blockers. These work by converting U.V. to heat and letting it dissipate, rather than killing your cloth. In the process, the little blocker bits get used up and they need to be renewed from time to time. 303 Fabric Guard is one of the best U.V. blocker repleneshers available for fabric, as well as being the most commonly available source of fluorocarbon water repellency.

    Any brushing or scrubbing should be done with something soft enough that it won't abrade the fabric (soft brush or sponge). If acrylic canvas has a weakness, it's it's lack of abrasion resistance compared to some other fabrics. Using abrasives or scratchy brushes on it is just asking for trouble.

    As for the mildew removal, standard treatment for synthetic canvas like Sunbrella (direct from the manufacturer's color swatch booklet) is as follows:

    "Sunbrella fabric should be cleaned regularly before substances such as dirt, roof particles, etc. are allowed to accumulate on and become embedded in the fabric. Brush off dirt, etc. and hose down with a mild solution of natural soap such as Lux or Ivory in lukewarm water (no more than 100 degrees F). Rinse thoroughly to remove soap. DO NOT USE DETERGENTS.

    For more stubborn cases: Soak the fabric for 20 minutes in a solution of no more than 1/2 cup (4 oz.) Clorox and 1/4 cup (2 oz.) Ivory or Lux soap per gallon of water at approximately 100 degrees F. Rinse thoroughly in cold water to remove all of the soap. This may remove part of the water repellency and the fabric should receive an application of an air-curing fluorocarbon water repellent treatment if water repellency is a factor."

    Considering that Sunbrella boat covers often price out in the range of $35-$50 per square yard of fabric used, stay away from home-brewed cleaning methods and away from that cabinet full of household cleaners under the sink. Follow the manufacturer's directions. You may or may not get all the dirt and mildew stains out and may have to live with some of them if it was allowed to grow for a long time.

    p.s. if your covers are cotton canvas, rather than Sunbrella (acrylic canvas), the process and chemicals used will be somewhat different. Let me know if you need the recipe for cotton and I'll post it.

  6. #6
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    Good to know Todd. I certainly stand corrected (thought 303 was the particular flavor of Scotch Guard you recommended, didn't realize it was a totally different product).

    - M

  7. #7
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    Yeah, it is strange how our culture no longer makes much of a distinction between soap and detergent -- the latter is known nearly everywhere under the generic term "soap". Sounds like it is critical in this case!
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  8. #8
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    Todd I would love the recipie for canvas.

    Also all stay away form the bleach if at all possible. not because it will change the color of your fabric. stay away from it because it will destroy the fabric itself. I would use a very diluted solution to insure no dammage to the fabric. don't believe me. soak a cotton undershirt in 1/2 and 1/2 bleach. the fabric will tear easily afterwards.

    some of the chemical bleaches can be used instead as they are not as dammaging but still use sparingly. also the non clorine bleachs won't kill the mildew.
    "those who loved you and were helped by you will remember you. So carve your name on hearts and not on marble."

  9. #9
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    Thanks for the suggestions. The cover is probably Sunbrella but I don't know for sure. How is it different from a cotton canvas?

    I use 303 for my mast boot but I haven't put anything on the boat cover since I've owned it. Maybe I should.. it's a lot of canvas though. It covers the entire boat and has sides that hang just past the rail.

  10. #10
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    Most cotton marine canvas is either light grey-green or natural cotton color (almost white with tiny brown fiber specks). The most common brand was once called Vivatex and is now called Sunforger. It would be fairly unusual for a custom cotton cover to be made from anything else. Sunbrella is more likely to be found in brighter colors. You can also pull off a loose thread and see whether it melts (synthetic) or burns (cotton).

    For cleaning mildew spots on a cotton cover, I think a scrub brush and laundry detergent is probably the best bet. Unlike synthetic fibers, where mildew clings to the yarns (or dirt and/or salt on the yarns) but doesn't saturate or actually eat the fiber, cotton is another story. Mold and mildew soak right into cotton and if left there, will eventually have your fabric for lunch. It's possible to use a diluted bleach solution on cotton, but it can and will weaken the fabric to some extent. The chances of getting all of the mildew staining out without using chemicals so strong that they may seriously weaken the cloth are not very good. After washing and rinsing, dry the cover thoroughly and apply a waterproofing/mildewcide compound made for canvas tents, like "Canvak". This comes in one-gallon cans and you brush it on or spray it with a garden sprayer, giving it a good soaking. Let it dry completely before storing the cover.

    ...and be very careful about using any kind of acid products on fabrics (cotton or synthetic). I've heard that in some cases, it can accidentally alter the Ph of the fabric and make it much more vulnerable to U.V. deterioration. Here again, thorough rinsing with clean fresh water after applying any cleaning product is required.

  11. #11
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    The cover is light beige, so I'm thinking it's not sunbrella. I've seen sunbrella and this actually seems a bit different. I'll try a laundry detergent and see if it does anything.

  12. #12
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    Smile Mold

    Awnswer - White vinegar with water. Removes the smell.
    I love the smell of fresh cut plywood in the morning.

  13. #13
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    Not the answer, it's an acid.

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