Marinette Boat Forum

Well we are on to Chapter 2 of Sunken 32. We pulled her a couple weeks ago for her yearly power wash and she was an absolute mess. Long story short.....we have now had the hull Dustless Blasted to bare aluminum and will be starting the welding/primer/paint process tomorrow.

Point to consider that you may have planned for - I Hope. Once taken down to bare aluminimum you must prime the hull asap.within hours. a day is too late because it begins to skin coat almost immed which means paint won't stick. So, it appears you have work to do (welding) ..but before applying any paint, re-sand --light sanding will be fine --everything you need to paint over. good luck

It's in the marinas hands now. They scheduled blasting for sunday, welder for monday (who didn't show today), so who knows whats going to happen. The two brothers who own the shipyard are very knowledgeable and really do quality work, so I sure hope they do some prep work before painting. That being said, blasting took 7.5 hours....so how are you supposed to get paint on a hull after 7.5 hours of blasting and then an hour of soap and water wash?

I hate to say this, but aluminum corrodes INSTANTLY when sanded (ie: you can't paint it fast enough!)

Don't believe it? Then try this little test. It's called the Guedian Brothers Technique. To wit:

Mix up some clear epoxy, then "wet sand" some bare aluminum with it using coarse sandpaper. You'll immediately see the clear epoxy turn grey, as the Al Ox layer is being mechanically removed. This is a really good way to make sure paint will adhere, but kinda impractical for a 3 foot boat like this!

What to do, what to do... Paint companies sell an etching primer (Alidon?) with phosphoric acid that removes the oxide layer and temporarily adds a film that accepts paint with good adhesion. After that comes the epoxy barrier coats, then the anti-fouling. Did my old boat that way and the paint never came off (in over 11 years).

Good luck!

Jeff

PS: Right happy I trailer now.

honestcharlie56 wrote: blasting took 7.5 hours....so how are you supposed to get paint on a hull after 7.5 hours of blasting and then an hour of soap and water wash?

Easy..you tell the marina to be damn sure to have someone on hand when the blasting ends and get a coat of primer on there and and then. NOT the next day. Sorry to be so insistent in tone. But you will be totally screwed otherwise.
Actually, that is an exaggeration. You will not be totally screwed..the paint will fall off and because it's an aluminum boat that will skin over quickly when the paint falls off and is resistant to rusting anyway, it will last a long time but will get lots of growth and critters and look ugly.But the boat won't rot.
You're an M guy - we love ya and don't want to see unnecessary consequences. Would love to hear what marina says

(I had blast/paint same day experience/marina was totally onboard

I sand blasted where I was going to weld. Did all the welding then blasted the rest. Lightly blast the exposed aluminum again. Yes, you can get metal etching primer with phosphoric acid in it. Have used it on airplanes, it works very well.

I am quite aware of aluminum oxidizing the second its exposed to atmosphere. Like I said, its in the ship yards hands. We discussed etching primers and acid washes etc. I guess I'm more interested in the whole "do it the exact moment the blasting is done". Its literally impossible. The blasting process took 7.5 hours. Once its done it literally took two soap washes to clean the surface of all glass media. I'm not sure you can get away with not using an etching primer or an acid.

I don't think "the minute after" is a required standard..but certainly within a few hours or less. Your best guide: your paint mfr's tech people.
I do think priming the next day is too long a wait. IMHO

All of you Marinetters out there ought to try the Gudian Brothers Test I described above. All you need is a piece of scrap aluminum, some cheapo clear epoxy, and some coarse sandpaper. The results are stunning the first time you see it, and extremely educational!

Jeff

If I get a spare minute I will, it sounds interesting....and will probably make my insomnia much worse concerning this paint job!!