How To Clean and Waterproof Marine Canvas Part 3

In Part 1 and Part 2 I explained my journey to this point – ready to try an eco-friendly alternative that would allow cleaning and treatment of marine canvas on or near the boat in the water. After trying the conventional method, I knew there had to be a safer way for both people and the environment, and sure enough, I was able to find a few products to help.

A product called MoldOff exists, which claims to kill and neutralize mold and mildew naturally. Spray on, leave for 24 hours, then wash as normal, and the mold should be gone. It’s touted as totally biodegradable and eco-safe. Sounded great anyway, so I thought it was worth a shot. I also came across one lone eco-friendly waterproofing spray – Star Brite Sea Safe Waterproofing Spray. Touted as “lake safe” and safe to use near water, I thought it was the best place to start.

Following the instructions on the MoldOff, I thoroughly sprayed down a particularly bad soft top on a client’s Duffy 22 electric boat. The top is nearly flat and had become overgrown with mold and algae, deep into the fabric. I soaked the top and left for the day, hoping for good results. I returned a full 48 hours later – longer treatment the better, right? – then commenced a thorough washdown as usual with lots of gentle scrubbing of the top. To my dismay, the top looked the same after it had been washed and dried, and I thought I must have beat the MoldOff with this one. At the owner’s request, I went ahead and waterproofed with a single, soaking coat of Sea Safe Waterproofing, per the instructions, and left it at that.

But surprisingly, the mold and algae soon began to disappear. My guess was that, because the MoldOff had killed the mold and algae, the stains in the fabric began to fade quite quickly in the sun. Within a week or so, the mold and algae stains were merely shadows of what they once were, and viewing it from the dock, the canvas appeared to have nearly completely changed color. The waterproofing seemed to bead quite well too, although with the age of the canvas and complete lack of waterproofing to start, beading was short lived. 6 months later though, the canvas was still water resistant, with the water only penetrating the very surface of the fabric and drying quickly. A second coat at that time would probably bring back nice beading for a little while.  

For the most part, the mold has not returned. In one small spot I re-applied mold off as a preventative measure one time, but other than that, the first treatment seemed to do the trick. Of course, I expect that the mold and algae will return quickly if I let the waterproofing wane as badly as it had originally.

We have now treated canvas on several other boats, probably almost two dozen different covers, biminis, and more, and the process has provided consistent results. Once canvas is pretty moldy, it’s probably always going to show some light stains from it, battle scars of sorts, but the MoldOff seems to work well to stop and kill the growth, and the Sea Safe Waterproofing keeps the water and contaminants out to prevent new growth.

We have also treated newer canvas that had no mold growth, simply with the Sea Safe Waterproofing. These covers were still waterproof but no longer beading at all. One coat of waterproofing and the covers are back to beading when misted, almost six months on. On some older covers, it's been taking an extra coat or two of treatment to get to the desired water-beading, but it can be done. 

All in all, I think this is a great compromise for a method that allows for cleaning and treatment of the canvas on the boat and/or near the water, without all the environmental and personal hazards to worry about too. Seems like a win to me.


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