Treating inside of canvas

David Satter

Wooden Canoe Maniac
I do a lot of square sterns here. I think people don't want to flip them over to dry when they get wet inside.
So when I recanvas, the old canvas has mildew/mold on the inside. I'm using #6 72 inch wide canvas. I don't think anybody carries treated canvas that size. I wish I could treat the inside of the canvas with something before I put it on. I don't want to get too crazy and experiment with anything new. Maybe a mold blocker or something I could spray on the inside. I know this has been talked over before, just took another one apart yesterday and though about it again.
 
For what it's worth I mix 2 bottles of M-1 mildewcide with the canvas filler. The filler completely saturates the cloth so I figure the mildewcide gets carried in in there too. It always seems to mix well. One little bottle is supposed to work with 1 gal of paint - I figure 2 bottles work better than 1.
 
Yes I mix that in with my filler also Howie. But I don't believe it gets through to the inside of the canvas enough to prevent mildew/mold. Especially with the heavier canvas.
 
The unwillingness to flip boats over to dry when they get wet inside is probably part of the reason why canvas covered boats have an even lower historical survival rate than canvas covered canoes. This appears to have been true even when lead based fillers and paints were in common use. These are much more toxic than anything readily available today. This may not be a problem that you can easily solve with chemicals.

Benson
 
I agree. I do give my customers care and maintenance instructions. But that doesn't always help.
 
Saturate the canvas with zinc naphthenate after installation. It also shrinks it tighter.
 
Rob, is this something you "paint" on once the canvas is tacked in place or do you soak the canvas in a tub etc prior to applying Thanks
 
Being from Canada as well I also use the same preservative Rob has suggested. It is very strong smelling and must be applied outdoors. I usually brush it on the areas most susceptible to rot, such as beneath a keel, the ends, and under the outwales. I then spay it on with a squeeze bottle on the remaining canvas. I've never had any issues other than I smell like it for a few days after.
 
It's not the outside of the canvas I worry about. It's the inside. Between the floor planking and the canvas where water can settle. If not turned over to dry once in a while water can settle in there.
 
Sorry Dave I should have been more clear, I understand your concern but when this preservative is brushed on it soaks completely through the canvas thus treating it entirely.
 
Oh, I'll look into it a little more. I'm a little hesitant about trying a chemical like that on canvas and a customer's boat :)
 
Zinc naphtenate is difficult to find in the US. Years ago, copper napthenate was available in the US, but I haven't found it in some time. Heavyweight Dacron is an alternative, if you can find it. North Cloth might pull some 14oz. greige goods before the second heat set if you contact them and order enough to make it worth their while.
 
I use the same (clear preservative) since our climate is rain and more rain. But it is perfect conditions for mold, rot, fungus and mushrooms. It is harder to find as many outlets don't want to carry the dangerous stuff anymore. It does smell a lot so need to do outside and let it off gas for a while before I add fillers.
 
In a similar, but different vein; I've always wished I could treat the inner surface of the canvas with some sort of water repellent. I think that the exposed inner surface of the raw canvas is a weak link in our building process. It allows the canvas to absorb water from inside the hull, gain weight on a trip, and create paint blisters if the boat is not dried-out in the upright position.
 
I think you will find that the clear preservative will soak right through, which is why I only recommend the clear as brown or green will stain the wood inside. I have never had any blistering from wet canvas.
 
Shelidrake, Before stretching the canvas . spray the inside of the canvas with the heavy duty outdoor scotchgard. It will waterproof the inside of the canvas. Though may not protect from mildew.
 
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