Join Date: Feb 2013
Location: Port Dover, Ontario
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Re: Soda blast/ chemical peel bottom paint build up
My qualifications to have an opinion: Gel-stripped a Tanzer 22; Sanded bottom (and repaired about 1300 blisters on) a C&C35, and observed a sailing buddy soda-blast a C&C30.
Gel-stripping - messy, sloppy, toxic process. Temperature and weather sensitive, so not always a good option in Canadian spring weather. When I got down to the end, I had to sand anyway, to get the residue off the gel-coat, which either requires a day to let the stripper dry, or a bunch of gummed up sandpaper. This was a time-consuming process, and not as effective as I imagined. Stripper was expensive. (double entendre!! fun!) I think I spent $300 on stripper, and another $20 on sandpaper afterwards. ended up throwing out 5-6 scrapers at the end, as well.
Sanding old paint off - REALLY time-consuming. You shouldn't use high-speed removal devices like belt sanders or grinders, according to all sources. I used a belt sander to take off the thickest stuff, and then went to a RO 1/4 sheet sander. Figure it took me 30+ hours on the CC35. Boat yards may expect you to hook up a filter/vacuum, etc. Toxic dust is next to impossible to keep out of bodily orifices. Respirator recommended. Leaves the boat perfectly prepped for repair/repaint, etc. Cheapest option BY FAR (excluding labor). I think I spent less than $100 on sandpaper, dust masks, etc.
Soda blast - big production. Need to get yard's permission. leaves the boat bottom in devastated condition. Any epoxy/paint work subsequent would need extensive sanding to prepare. There is a theory about not being able to control depth of medium ingress, leaving pin-holes for water/osmosis issues - Epoxy barrier coat negates that, I think. This took an afternoon, and my buddy stood around with a beer in his hand. (I started sanding the bottom of my boat in January, every Saturday for 2 hours. He called a guy, and accomplished the same thing in 4 hours.) cost about $700 for a 30-footer.
Draw your own decisions from that. I'm cheap, and I like being near my boat, even in 3 feet of snow. I will continue to sand, but I'm not sure it's the 'right' answer.