View Full Version : Treating canvas sails

Ron Turner
07-22-2001, 10:01 PM
Looking for advice regarding using a mildewcide on new canvas. Have been considering using a Zinc Napthalate known as Zinctox. I'm concerned that this material could attack the material.

Also, I'm confronted with removing mildew stains on older sails. Has anyone experienced problems using chlorine bleach (about 6% and 1/20) How long should the canvas be exposed to the bleach and will the bleach deteriorate the fabric?


07-22-2001, 10:48 PM
Ron, I don't know if the zinc napthalate will have a negative affect on the canvas but, in a strong enough solution or left in contact with the canvas long enough the clorine definitely will. Pure clorine bleach, in out of the bottle concentration, will destroy canvas after soaking for a few hours. In a dilute form you should be ok. I would say that you should go ahead and use the clorine solution as you've suggested (along with the usual rinse regimen of course).

What concerns me isn't the canvas so much as the sizing and what affect any chemical will have on that. Let me check on what info I have about it at work tomorrow and I'll get back to you...

Todd Bradshaw
07-23-2001, 01:41 AM
The most common preservative for cotton sailcloth these days is called "Canvac". It is also used on cotton tents, etc. for water repellency and mildew prevention. It's clear, sort of waxy and contains Zinc Napthalate as a mildewcide. I don't know how much it contains, so I can't compare it to Zinktox. Most of the other mildew preventing chemicals are pretty nasty poisons that you probably don't want on your sails.

Stained sails: First wash with mild soap and water and scrub mildew with a brush. Bleach with 1 part Clorox to 10 parts cold water. I wouldn't soak it more than an hour or two, then rinse the hell out of it with water. There is no way to prevent bleach from damaging cotton to some extent, so don't overdo it and really rinse it well. Dacron is less prone to damage from bleach, but I still wouldn't go crazy with the stuff. The resins on Dacron sailcloth are generally melamine or epoxy, baked-on at several hundred degrees and should not be affected by the 1 part to 10 parts solution.

Stan Derelian
07-23-2001, 09:17 AM
I work with textiles, and if at all possible I would avoid chlorine bleach, even diluted or use it only as a last resort. While you might not notice it at first, it will weaken the cotton, and shorten its usable life.

Your could try a borax solution, heated, or a concentrated solution of one of the commercial non-clorine laundry bleaches.

07-24-2001, 04:36 PM
Oxalic acid works well to get out rust stains but wash well afterwards. Plenty of air is needed for cotton/flax sails.

07-25-2001, 01:50 AM
Todd, thanks for reminding me about those other mildewcides/fungicides... I believe that the nasty stuff you are referring to are clorothalonil based products. It is the clorothalonil that is nasty (I have read the MSDS). Once it is cured (usually mixed into paint) it is OK to be around but handling it requires PPE and carbon air filters and it is not real good for the fish. Not good for pregnancies either.

Brad Faus
07-25-2001, 09:57 AM
Nice to see I'm not the only one with a cotton sail. After having so many lofts tell me I didn't want one, I ended up with a used one from Bacon's that I had re-cut. Rust stain patina at no extra charge. What loft did you buy a new cotton sail from? I would like to know for the future. Also, I didn't know what to treat mine with, so thanks to all for that info.

Todd Bradshaw
07-25-2001, 01:13 PM
Some of the preventative treatments also contain arsenic and other similar stuff. When the conditions are bad and you're pulling down armfulls of flogging sail, the last thing you need is to be poisoning yourself in the process.

Brad, the keys to getting a good cotton sail these days seem to be finding a sailmaker who first of all has access to good fabric and secondly has built enough sails from it to know how and how much it will stretch. It's not as predictable as Dacron and previous experience with a specific fabric really helps when it comes to broadseaming and shaping the sail. If I was looking for a cotton sail in the U.S., I'd probably start with Nat Wilson, though there are bound to be a few others worth checking as well.

Ron Turner
07-25-2001, 08:32 PM
We've been building canvas sails for many years for our schooner which has six of them measuring about 2,000 sq. ft. Canvas is a delightful material to work with; to furl and handle, repair and maintain compared to synthetics. Unlike synthetics, however, they cannot be ignored. Recently we discovered that they had no tolerance for synthetic sail covers.....they simply baked beneath them and began growing mushrooms. Today's boats have become such a cellection of man made materials that they are more closely related to automobile than boats. Except for the high performance of marine synthetics, I find no pleasure in dealing with today's resinous fleet. Besides, my sewing machine definitely does not like dacron.

Thank you all for your help in this matter.

Dale Harvey
07-26-2001, 08:18 AM
Recipe from an old Gulf Coast schooner captain. Boil in a large kettle with Alum. Rinse in seawater,spread in sun to dry/bleach. Then rinse with freshwater. Operation was generally carried out on the beach on a calm day. I have no idea where to buy Alum.

Alan D. Hyde
07-26-2001, 10:12 AM
Dale, alum is used for flocking swimming pools, and is available at any pool supply store.

It runs under $1 per pound around here, less in quantity.