A few years back, we purchased a heavy duty Sailrite sewing machine. It has been incredibly useful in creating an assortment of items for our Alberg 35, s/v Mystic. Among the projects we've completed are storage bags, winch covers, dinghy chaps, rain and sun tarps, and a winter cover.
The cover was our biggest project, taking a total of 50 yards of SurLast water repellent fabric. We got a great deal purchasing it from Rochford Supply's seconds bin for $5.00 per yard. The project took six weeks to put together but has proven to be well worth the work. It has protected our boat for the last five years, keeping her dry and shading her teak from the sun. Each spring, we inspect, clean and make repairs where needed. In spite of the exposure to the elements, it has held up nicely with only minor chaffing damage.
Last year, we decided to re-waterproof the canvas in the hope of extending the life of the cover. Over the counter spray products are easy to find but proved to be expensive. Dave researched making our own and found a recipe on one of the boat forums he follows. We decided to take it on as a DIY project.
There are only two ingredients in the waterproofing solution, silicone caulk and mineral spirits. We combined them in a large bucket then blended the mixture until the silicone completely dissolved into the mineral spirits. The amount of fabric we were working with required tripling the recipe. After cleaning the cover, we laid it on a poly tarp face up and rolled the waterproofing mixture over the entire cover, making sure to saturate every inch, then hung it outside until it was dry.
The fabric felt a little stiffer than before the treatment although it didn't feel heavier and it didn't smell like chemicals. Last fall, we installed the cover and crossed our fingers. When we returned in the spring, we found that a pocket of snow had accumulated over winter. As it melted it created a deep sag in the fabric, bulging downward with about 5 gallons of water. We were amazed to see that not a drop of water seeped through. The waterproofing did it's job!
I have to admit that I was a nervous about using a home-made recipe instead of purchasing a commercial product. I didn't want to ruin our cover. Not all fabrics can handle these chemicals, including Sunbrella. We researched SurLast and felt confident about the compatibility before beginning this project. We experienced a successful outcome and plan to use this method on our other boat canvas.
Waterproofing recipe:
10 oz tube of 100% clear silicone caulking
1 gallon of odorless mineral spirits
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