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Thread: Canvas Sails & Mildew Stains

  1. #1
    Join Date
    Aug 2005
    Rhode Island

    Default Canvas Sails & Mildew Stains

    How do you remove mildew stains from canvas sails?

    The real question is, how do you remove mildew stains from canvas sails, without destroying the canvas!?

  2. #2
    Join Date
    Sep 2004
    Cape Fear, NC, USA


    How To Remove Mold and Mildew
    From David Sweet,
    Your Guide to Camping.

    Mildew, a dark residue left by mold, can leave a stubborn stain. If mold or mildew has invaded your tent, canvas or awning, you can easily remove it.

    Here's How:

    1. First, kill the mold.
    2. Brush the mold and mildew from the material.
    3. Wash the affected area with a solution made up of 1/2 cup Lysol to a gallon of hot water.
    4. And/or rinse with a solution of 1 cup of lemon juice and 1 cup of salt to a gallon of hot water.
    5. Allow the material to dry in the sun.
    6. Next, bleach the mildew stain.


  3. #3
    Join Date
    Mar 2006
    Victoria, BC


    Hi Steve - are they cotton canvas? Bleach will weaken cotton (natural) fibres, so I'm not sure I'd use bleach at all. I'm not sure about the effects of Lysol - maybe get a scrap of cotton canvas from a local store and try the solutions before hitting your sail with them. Perhaps the site explains what each solution does...if the natural lemon/salt mixture will suffice, that may do it.

    And, obviously, once you take care of the stains, never put them away wet to avoid the problem in the future.

    Let us know what you do and how it goes.

  4. #4
    Join Date
    Apr 2006


    OK smarties... so how do I get rust stains out of a suit of North Sails? The previous owner folded my sails up like a laundry pile.

  5. #5
    Join Date
    Jun 2000
    Madison Wisconsin


    For rust on Dacron you want to dunk the stained area in a solution of 1 oz. oxalic acid per pint of hot water. Wash well (a little dish soap in water, followed by a thorough rinse) after the acid bath.

    Bleach has been used on both canvas and Dacron over the years (1 part clorox to 10 parts cold water, followed by a good rinse) but on natural canvas it does have the ability to seriously weaken the fabric if left too long, so caution is advised. Unlike Dacron, where mildew mostly sits on the surface, cotton can really get it deep and by the time you get all of it out, there may not be a lot of integrity left in the cloth, so you may be better off living with some staining.

    I wouldn't be surprised if some of the modern "bleach alternative" products might work and be safer on cotton than regular bleach, but I haven't tried any or heard any reports of people trying them. In any case, remember that the insides of built-up areas (like corner patches) will probably take three or four times as long to dry as the rest of the sail. The finished sail can be treated with products like CanVac if desired, which repel water and also contain midewcides to help prevent growth. The potential downside is that the mildewcide is usually some sort of arsenic-based stuff. Handling such a sail and then eating a sandwich wouldn't be very high on my list of healthy things to do.

  6. #6
    Join Date
    Aug 2005
    Rhode Island

    Default What we did

    Here's what we did to cure the mildew stains on our canvas sails.

    1) Put a query in the Wooden Boat & Classic Boat (UK) forums

    2) Wait for brilliant answers that we never thought of

    3) Carefully evaluate approaches & chose this suggestion from Classic Boat UK :

    "Give them to your sailmaker for a valeting. Impress upon him the fact that they are cotton and you want the mold stains removed. When they come back all out of shape, and with holes bleached in them, get him to make you a new set for free.
    Simple really. " -- Mariposa (!!)

    HOWEVER, here's what actually happened.

    Sails were washed cold, gentle cycle, in a front loading commercial washer and air dryed. Simple Green for soap. No bleach in wash.

    A couple of bad spots were scrubbed with a plastic hand brush & some Oxy 5 non-chlorinated bleach -- did a good job. (Hope that was OK)

    We accepted that the gray stains were there to stay if we didn't want to kill the sail in the process.

    We sprayed the sails with RhinoHide UltraBan ( mold preventative film, as recommended by a prominent Maine sailmaker.

    We're happy with the result but realize this probably wouldn't have been a problem if they had been sprayed with RhinoHide once a year from the time they were made.

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