A painful experience by a then novice owner.
We decided, being new to Marinettes to have a yard paint the bottom. The yard that painted our boat Fortunato placed a large amount of effort in not completing the job on time nor correctly.
We had decided for reasons of own future maintenance and ease of repair to avoid any solution that we could not do touchup painting for ourselves. (i.e. using TBT like Alumacoat II). A lot of people here like the Pettit paints, also.
(Pettit recommends Metal Prep, then primer with either Quick Dry Zinc Chromate Primer or High Build Epoxy Primer, and finally Alumacoat II as an antifouling). Pettit recommends their High Build Epoxy for sandblasted aluminum or large areas.
The yard while amazingly slow, did complete the job in an adequate manner.
Since our boat had been in salt water, we purchased Chlor*Rid salt remover for the pressure wash after the sandblasting. (Gets the trace salts out of the metal.)
1) Yard sandblasted the bottom, including the Capac sensor. Since sandblasting this sensor (it has a special silver coating) destroys it, we were of course in instant need of a replacement sensor (Hint a can lid can cover the sensor, so that the sandblasting does not damage it.) (Capac Reference Electrode 32622, cost the yard $200). Paint also damages these, otherwise they last 20-50 years.)
2) Yard let the boat sit (Not a good idea, but will work if you use an etch, but is not recommended). The cleaning and painting Should be right away
3) Yard pressure washed, we insisted on them using Chlor*Rid, since Fortunato was a salt water boat. Noted that some fixes were needed from pitting, but the hull was OK to paint. I'm told that a lot of salt water bridge companies and commercial shops use salt removers on metals.
(Next time, some small spots of aluminum will get replaced.)
(Interlux recommends a powerful vacuuming to clean sandblast.)
4) Yard let the boat sit. (Argh!) Take pictures of the process, you need them if they screw it up.
Painting Cycle Started - Once the first coat of paint or etch goes on with Interlux, you're on the clock.
5) Yard painted bottom (spray) with Viny-Lux Primewash (an Etch Zinc Chromate). This is absolutely critical to good paint adhesion on aluminum for Interlux epoxies. (Some Zinc Chromates primers are self etching, but for painting aluminum with Interlux epoxy, get this stuff.)
Note : Primocon is a good patch primer for aluminum when you're fixing some bare spots, and you have an uncertain base. (I use this topside as the primer (with Viny-Lux) under fittings when I find the aluminum underneath is exposed.)
6) Next 2 days, Spray coat of Grey Interprotect 2000E 2 part epoxy, 2 coats when on in the first day, 3 coats on the second day. Interlux recommends a certain thickness, 10mil, which should be covered by 4-5 coats, however many Marinettes use extra coats. Time is of the essence here, the coats can't be over dry for the next coat to go on. Follow the paint manufacter's recommendation.
7) Drying 2 days and 3 coats of Trilux. Trilux should have alternating colors red, then blue, but the yard didn't do that.
8) Wait for the engine to be fixed, replacement of sensor, and then started boating in June 2001).
9) Find a new repair yard.
Generally I am happy with the Interlux 2000E system, It's held up ok for 3 years with NO exposed aluminum. Supposedly Interlux does well on spark tests. (I'll try to get a writeup from an expert on sparktesting paint.)
Buy the right thinners for each paint used.
Check the Marinette forum messages, there's a lot of good advice out there. Post questions for help.
Get the right sandblasting material for aluminum. Get someone smart enough not to sandblast the sensors.
Don't ask the marina about the shop, ask someone who boats at the marina.
Can the yard speak Marinette? Some speak better than others.
Can you do it your self? Hire a sandblaster and save a bundle. I think bottom painting is best done by an experienced owner or one with help from a experienced Marinette owner, not a shop.
Aluminum must be rough to have epoxy paint adhere to it.