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artwork · 04-17-2008, 08:26 AM

Alanglios, I've attended a couple aluminum paint seminars at IBEX (Internat Boatbuilders Exhibition) and they are consistent in their proceedure. For new or bare aluminum - sandblasting is best - not soda or walnut shell, but medium grit sand. If blasting is not practical, sand with 80 grit, this gives the best 'profile' for paint adhesion. Then prime with an epoxy primer to build a barrier coat - this could be up to 4 or 5 coats, then a non-cu bottom paint. If you have pitting and want to fair it out. The fairing goes on after the first epoxy primer. The epoxy fairing compound chemically bonds to the primer.

The VERY critical part of this process is time. Get the primer on IMMEDIATELY after sanding. The boatbuilders and paint people concurred - what you sand in the first half of an 8 hr shift, you must paint in the second half. If you can be painting within an hour, all the better. The aluminum will start oxidizing that fast. If your yard sands one day and paints the next, it's too late.

As a sidebar, there was a fellow attending the seminar who worked in the paintshop of a megayacht builder who said they no longer sandblasted, but used the chemical etcher -Alumiprep. I sandblasted the bottom of my 58 and zinc chromated it as a holding coat. This took a bit over three tons of sand, at least half of which is still in my boathouse, but the topsides are too big of a job to imagine doing this again, so I'm thinking chemical. I spoke to International paint and they admitted that the 'old standby zinc chromate' is as good as any primer, just sand it (80 grit) when I'm ready and begin the epoxy coatings.

04-17-2008, 08:26 AM	#12
artwork Registered User Join Date: Feb 2006 Location: Lake Huron Posts: 24	aluminum prep Alanglios, I've attended a couple aluminum paint seminars at IBEX (Internat Boatbuilders Exhibition) and they are consistent in their proceedure. For new or bare aluminum - sandblasting is best - not soda or walnut shell, but medium grit sand. If blasting is not practical, sand with 80 grit, this gives the best 'profile' for paint adhesion. Then prime with an epoxy primer to build a barrier coat - this could be up to 4 or 5 coats, then a non-cu bottom paint. If you have pitting and want to fair it out. The fairing goes on after the first epoxy primer. The epoxy fairing compound chemically bonds to the primer. The VERY critical part of this process is time. Get the primer on IMMEDIATELY after sanding. The boatbuilders and paint people concurred - what you sand in the first half of an 8 hr shift, you must paint in the second half. If you can be painting within an hour, all the better. The aluminum will start oxidizing that fast. If your yard sands one day and paints the next, it's too late. As a sidebar, there was a fellow attending the seminar who worked in the paintshop of a megayacht builder who said they no longer sandblasted, but used the chemical etcher -Alumiprep. I sandblasted the bottom of my 58 and zinc chromated it as a holding coat. This took a bit over three tons of sand, at least half of which is still in my boathouse, but the topsides are too big of a job to imagine doing this again, so I'm thinking chemical. I spoke to International paint and they admitted that the 'old standby zinc chromate' is as good as any primer, just sand it (80 grit) when I'm ready and begin the epoxy coatings.