Mailport January 2012 Issue

Mailport: January 2012

Bottom Blasting

Have you done a piece on ice blasting paint off a hull?

Bruce Rosenzweig
Via email

I read with interest the recent article about sodablasting (October 2011). Unfortunately, the boatyard I frequent insists that blasting with ground walnut shells is the only way to go. I am very interested in your take. Thanks for your input.

Bob Child
Lagoon 380

When it comes to blast media, the three big concerns are abrasiveness, surface preservation, and cost. Ground up walnut shells have been used for blasting for decades. Like soda, it cuts paint but leaves the gelcoat. And just as sandpaper is rated by grit, blasting products are rated by various numbers, including mesh size, density, and a hardness, or Mohs, number. As with sandpaper grit numbers, the lower the mesh size, the coarser the blasting medium. Mohs numbers go the opposite direction; a higher Mohs number means a harder medium. Walnut shell comes in a range of mesh sizes and shapes, so blasting results can vary. Fine, round shell, for example, will be less aggressive than larger, irregular shell. So it pays to know what mesh size walnut shell your blaster is recommending. The idea, of course, is to use something that is effective on paint, but harmless on gelcoat. While the finest mesh size walnut shell compares to baking soda (mesh size range from 50-170), it also comes in much coarser mesh size. For a newish FRP boat such as yours, soda blasting would seem to be the best choice, but we’d not write off a fine mesh-size walnut shell, which has served fine for countless paint-removal projects. Remember, the skill of the operator is just as important as the blast medium, so we’d recommend going with someone who specializes in paint removal—not the jack-of-all trades with a rented blasting gun.


As far as blasting with dry ice goes, it is a very fine blasting media, but it’s more finicky and more costly than soda—plus there are CO2 emissions to worry about. We have not heard of it being used on boats, but it would seem a possible option as it is used for manufacturing molds.

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