How To Clean and Waterproof Marine Canvas Part 2

So now that you know from Part 1 why it’s so important to keep your canvas water resistant, where do you start. This is where I was a year ago, and consultation of Sunbrella’s website, Google searches, and YouTube videos all came up a bit short for me. Sunbrella extolls the benefits of regular, gentle washing as the single best thing to do. Once their waterproofing wears thin, they recommend use of a product (and a very effective one I might add,) by the name of 303 Fabric Guard to restore water repellency. Should the canvas be heavily soiled, Sunbrella recommends a mix of bleach and water and a soft brush. While the bleach is safe for the fabric itself, it may not be for the stitching however, so they urge caution before resorting to this step.

This all sounded a bit lacking for me, especially once I considered the hazards of bleach, and the warning label on the waterproofing product that they recommend. These aren’t solutions that can be used on the boat, or near the water for that matter. So what do I to do with large marine covers, biminis, and the like that can’t be removed, or can’t be moved very far from the boat?

As a place to start, I tried their recommended method on a few fairly soiled, small canvas covers. While the bleach solution was effective at cleaning up the surface of the fabric, it didn’t do much to remove mold and algae that had actually grown into the weave of the fabric, although it did lighten the stains up a bit. Even with multiple applications of the bleach solution, at some point the stains were there to stay. This was a bit disappointing. Below are some of the growth speckles remaining in the fabric after bleach treatment of one cover.

lingering mold speckles after bleach treatment

Next came the application of waterproofing. Based on the warning label, I gloved up, wore long sleeves, and a decent P95 face mask. Apparently this stuff is pretty horrible for you if you inhale it. The other conventional marine waterproofing products on the market are no different, as I discovered.

In spite of the hazard and petroleum odor, the waterproofing dried rather quickly in the sun, and showed strong water beading after it had fully dried. Success of sorts, but I had also confirmed that this would be difficult, if not impossible to do near the water, what with the bleach runoff and petroleum-based overspray and all.

That’s when I started researching more eco-friendly alternatives to serve these two roles, a cleaner/mold killer first, then a good waterproofing after. The choices were few, but I managed to find solutions that I think provided results just about as good at the bleach and 303 Fabric Guard.

Read on for Part 3 where I explain the products and process I used to resurrect some pretty nasty canvas, and protect and preserve some good canvas for easy care and cleaning.


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