Sand Blasting

[Boomyal]

Re: Sand Blasting

Thank You Boomyal! If I am going to do this by hand, I know I will be doing some scraping. The vast amount of the corrosion is bubbling under the Black paint. I have scraped off the paint where corrosion is evident which comes off VERY easy leaving bare aluminum.

That bare aluminum still needs to be treated prior to Priming and Painting, doesn't it?

Where the corrosion is not apparent under the Black Paint, I intend to ruff it up ,prime it and paint it.

Am I heading in the right direction here with doing it by hand?

Lindy, I taped and sand blasted the outer face of my intermediate housing, just enough to get any loose stuff off. On the outdrive, I pulled off all of the little pieces and sand blasted them. Leave the forward facing part of the outdrive alone.

Sand the outdrive with 80 grit wet and dry, using water with dishsoap in it. Some places you'll go to bare metal, some places you won't.

Immediately flush everything off, give it a vinegar bath, then wash it with the amonia, dry it all thoroughly then hit the bare spots with zinc Chromate.

Then overprime and shoot your cover coat.

You can see the results in my pictures. They well endured the summer boating activities. This having to respray every year is due to inadequate prep and the wrong paint. Only in places that you drag thru the sand, should you have to repaint that often.

 

[Sorrento 25]

Re: Sand Blasting

All bare aluminum needs to be treated prior to painting.

Various methods will work. SEM paint products are very good for spraybombs. The key is proper surface preparation at every stage of the process.

My experience is in auto restoration and typically with a project like this I would feather out the paint adjacent to the corroded areas with a 180-220 grit mechanically removing as much corrosion as possible. Sand the adjacent paint back until you get a clean feather edge with good adhesion to the aluminum. Don't worry about sanding the good paint yet.

Now follow the directions and prep the aluminum with a product of your choice such as those sold by Aircraft Spruce. Most auto paint manufacturers such as DuPont make products for this purpose and they should be readily available at a local body shop supply company along with SEM products. Follow with two coats of a self-etching primer (SEM 39693) over the bare metal areas.

Allow to cure and very lightly sand the primer and the unsanded areas of the original paint with 320-360 being sure to sand back the primer overspray so that it feathers out into the sanded original finish adjacent to the bare metals areas and so that none remains over unsanded paint. Take care not to sand through the self-etching primer to bare aluminum or it will have to be reapplied. Sand just enough to smooth and evenly scratch the surface for mechanical adhesion, and then follow with two coats of a filler primer (SEM 42013).

Sand again with 400 and topcoat with the best paint you can find. I'd bring it to a bodyshop for this part of the job if at all possible for a urethane or polyurethane topcoat.

 

[Boomyal]

Re: Sand Blasting

All sounds good Sorrento except for the 'self etching' primer. If by that you mean other than zinc chromate, that misses the mark. Typical self etching primers that you get at automotive paint shops are a poor substitute on bare aluminum.

Zinc Chromate is a regulated product, it is only available at marine and aircraft supply houses and is still the widely recommended primer for bare aluminum. And yes, urethanes would be the ideal top coat but very pricey compared to catalyzed automotive acrylic enamels.

If the outdrive was going to spend long periods submerged, I would definitely go with the urethanes, otherwise the catalyzed enamels will be miles better than Crustoleum.

 

[Sorrento 25]

Re: Sand Blasting

Well surely Aircraft Spruce has that!

http://www.aircraftspruce.com/catalog/cspages/zinc.php

 

[Lyndy]

Re: Sand Blasting

Thanks to all again. If someone in the future reads this thread, I am sure a lot of questions they may have will be answered. Will post pictures of my progress throguhout the Winter.