I read the comment about removing bottom paint, ending with directions, for after sandblasting, to "just wash off the dust and paint." I am familiar with industrial uses of sandblasting and remain incredulous: Can you paint fiberglass after sandblasting without further surface finishing?
Dan Dickison responds:
Good question. Thanks for making that point. You're right about the potentially damaging effects of sand blasting on fiberglass hulls. In his very useful book for used boat owners, This Old Boat, Don Casey holds that "fiberglass boats should never be sandblasted." Casey says that this approach might work on steel hulls, but sand blasting makes gelcoat porous, "and almost certainly leads to hull blisters."
In an earlier Ask the Experts answer posted on SailNet, Tom Wood suggests that water blasting (sand and a combination of water jetted onto the surface) is a feasible alternative to sand blasting. Certainly it would be a less destructive option. Another more benign option that's being tried at certain commercial boatyards is blasting with a solution that contains baking soda as the abrasive element instead of sand. The baking soda is mixed with water and both are jetted onto the surface to remove paint and other undesirable elements (tar, etc.) The baking soda works on a smaller scale than sand and thus doesn't remove as much material as quickly.
One additional problem with any kind of blasting is that it tends to leave an irregular surface that will certainly need to be refaired afterward. As you likely know, refairing a hull is time and labor-intensive job, and the expense of that work would probably offset any savings gained from blasting the hull instead of stripping it in more conventional ways.
Here's hoping that this response helps clarify any misunderstanding. Thanks again for making your point.