Soda Blasting Our Bottom

20 August 2008

There were many, many coats of old anti-foul paint that was dry, thick and flaky that needed to be removed. The normal method of using a scraper and hand-sander was going to be a huge job so, under advice of the painter, I arranged for soda blasting of the hull below the waterline to remove most of the old anti-foul.

This was a very interesting process to watch as first off they enclose the hull with plastic to constrain the over blow of powder. Basically, it is sand blasting but with baking-soda instead of sand particles, making it much more gentle but still a lot easier than sanding it off. It is horrendously noisy and I would not advise it to be done without informing you neighbours, if in your backyard. Even at the yacht club we moved to an isolated area where the noise would be less of a problem. It took the professionals about four and a half hours to do a 25 foot yacht hull after they had done all the preparation of the plastic bag cover.

They used about six large bags of soda for my 25’ hull and all the powder and anti-foul was dry and bundled up into the plastic and put in the rubbish bins. Due to our water restrictions, we were unable to hose down the boat and cradle but the result achieved in less than one day was impressive.

Although not cheap, it is comparable to what a professional boat builder or painter would charge you (in time charges) to sand off the anti-foul paint. If you can sand it yourself at your own pace, you’ll save a lot of money, but that was not an option for me. It is also a lot faster and the painter was very pleased with the small amount of preparation to do over the hull and around the waterline

I would certainly not call it a pleasant job but there is no method of removing anti-foul that it IS pleasant. It certainly takes paint off quickly to expose the original gel coat, as they gradually move down and around the hull. After the blasting all the painter required to do was to give them a thick sand and take off the areas covered by the cradle props.

It was very pleasing to know that there were no signs of blistering or osmosis in the hull below the waterline. The blasting would have shown any soft areas and did open up the normal pinholes of bubbles in gell-coat.

Next will be painting the hull below the waterline and eventually the topsides.