Primer Paint & Soda Blasting

I'm not from Missouri, but I do like to know what's required and when rather than just taking someone else's word.. When I repainted my Volvo outdrive shield and leg, I didn't sand or prime it - I just ran the soda blaster over it to clean it up a little before I nailed it with several rattle cans of paint.

Results:
The transom assembly and leg look perfect after our first, albeit slow speed, outing, but the prop lost paint on the front of one blade and the back of another (not due to contact with anything but water).

"They" say to use a zinc cromate primer and maybe even an etch before that when painting your water immersed aluminum. I might suppose that the factory 'etched' the metal before they primed and painted it - why would I have to etch it again? Likewise with the primer - wasn't it primed properly at the factory? If I still have paint on the unit, why can't I clean it and just rough it up a little before I paint it again?

There was no metal showing on the outdrive or tansom shield after I soda blasted it. And so far the generic paint is holding up.

The prop is a different matter. The first thing I did was to take it down to bare metal. Sanded it lightly, then cleaned it up with ammonia. While spraying it, I noticed some places didn't like the paint...the paint would pull away from small places like you might expect would happen with an oily surface. I could eventually, with enough coats, cover that area, but the whole process made me leary.

I got some acetone and wiped all the paint I could off the prop. Really gave it a good cleaning. There was still a minute amount of color on the prop when I sprayed it with generic primer. The generic white primer covered much better than the paint, but there was still a few small areas that 'rejected' the covering. I sparyed them over and over with the primer until they took color. Then I followed up with about 4 coats of generic white rattle can paint, the same kind as I had used on the transom shield. Well, that didn't work.

Here's the next step for the prop after the first outing.
Soda blast the prop again down to bare metal. I use a cheap soda blaster from Harbor Freight. Someone said, "Harbor Freight stuff is cheap, but like cheap whiskey and cheap women, sometimes it doesn't matter."

The thing about soda blasting is the control. I experimented and do believe that with a little finesse, one can take off one layer of paint at a time.

Soda is kind of friendly. I don't suit up for it, I just put a big fan in front of the work and blow everything into the back yard. This way I don't even need to shower after using the blaster. When I'm done, if there's a lot of white on the ground, a little spray from the hose takes care of it, but I usually just wait for rain.

So the prop is down to bare aluminum except for the back of one blade. I'll use it this way if necessary for the next outing, then when I have time I'll use the zinc cromate on a couple blades and then more generic rattle can paint. We'll see what's necessary and what's not.

Maybe I'm lazy, or maybe I'm curious?

Update as of Oct 2011. The transom shield and outdrive are still above expectation. The prop is a different matter.

I took the prop down to bare metal again and really cleaned it up with soap, ammonia, acetone and alcohol. Then I primed it with the green zinc cromate primer. Next time it was in the water, most of the paint came off, so I'm running it now as bare aluminum.