can i shoot automotive paint over zinc cromate on my lower?

[baja200merk]

i just painted my lower wit zinc cromate u know the green stuff and its a primer do you think i shoudl use some auto motive paint or spray paint over it?

[BenKeith]

I've tried on two different occasions to spray paint over zinc primer and never had much luck with it wanting to stay once the water got to beating on it. It did ok on the mid section but paint would peel off the lower unit. I've had much better luck with epoxy primer, as thin a coat I could spray and sand smooth. Not over thined, just sprayed thin. Then top coat that with a two part urathane paint, like Imron.

[Forkin' Crazy]

I think Ben's about got it. Epoxy is the way to go. The epoxy I use you don't sand if a topcoat is applied in a time window. Imron is a good choice too. Very durable, but like any aircraft paint, expensive.

It is not as pretty, but I use Sealer 1970... or 80...? Ditzler. It is a single stage non catalized sealer. Where I boat there are sticks and sand in the water and it ends up sand blasting the skeg and lower anyway. So... I just scuff it with a scotch brite and shoot a little on it. The one I use is light gray. It doesn't need thinning, so that makes it that much easier. A quart will go a long way. :)

[O/B Dude]

I have sprayed auto paint over zinc chromate primer with good results. You just have to carefully prep it and be sure to have a good mechanical bond..(rough it up) I prefer epoxy primer. The whole idea of the zinc stuff is that its bonds well to aluminum... but so does the epoxy primer.

[Blizz]

The reason that cromate primer had an advantage is that it was an etching primer and because aluminum almost immediatly starts to corrode the cromatestopped the process. I work in aviation and after years of use they found that it actually starts to cause corrosion (pitting) beause it will allow moisture to penetrate and then hold it there if you get a scratch in your topcoat. Epoxy is probably your best all around primer without spending big bucks. Ken

[racerx]

I think the brand is Dupont they make a self etching primer called Varaprime thats the best very very stinky.

[RSM]

What do you guys use for fairing compound after installing a BOB's low water pickup ?

[sho305]

I used the DuPont green etching primer on my force mid and LU. Then I put some leftover centari with a 2000 pack, the urethane conversion, on it. The LU was pretty pitted, and I had a new skeg welded on this little 85hp. After two summers I just checked it out closely. It has a couple scratches on the skeg, and the green is still on the metal there. The old metal LU is good, and the only thing I could find is a couple little bubbles on the intake grate vanes. It likely did not get sanded real well in them, and I never got around to putting any anode on it. It only sits in the water for a day if that, per week. I trim it out of the water. Of course it only goes 45mph or so too. I like that etching primer a lot, though I think the epoxy would help on there also. Didn't have any here at the time. I also painted the LU twice, about three coats each time, after I scratched it getting it back on.

I faired my transom with duroglass, but I am not sure you're supposed to use that and I covered it with epoxy. Tuff stuff.

[Blizz]

If you really want to get a real good etch they make this stuff called Alodine i'm not sure how easy it is to find but you put it on wait a few seconds and rinse it off it will turn your case an irridescent gold it also promotes adheision of your primer just an idea and of course any help you can get keeping paint on at high speed is great.. Just an idea Ken

[Forkin' Crazy]

You are suppose to use Alumaprep as the preping acid and then Alodine. The acid cleans any oxidation, and the alodine seals it. Nothing wrong with Zinc chromate. It has been used on aluminum products for years. And still is. But on the new aircraft, expoxy is used. That was my proceedure when I was painting aircraft. Strip, alumaprep, alodine, epoxy prime, top coat.

BTW if you do use alumaprep and alodine, wear rubber gloves. The acid will burn and the alodine will stain your hand and it will take a long time to wear off.

[Blizz]

If you don't have alumaprep you can just clean with scotchbrite until you get a water break free surface.. Cromate is fine just newer tests show that it allows moisture through that is one of the reasons aircraft companies don't use it anymore the other big one is cromate highly carciogenic (spelling).. Ken

[sho305]

Mine had lots of pitting on the LU. Lots! No way to get it right without sandblasting to start and I was not able to do it then. So I sanded it a lot, then scrubbed it with scotch pad and soap. Blew it off, solvent washed it, and painted. Was not worth it to try and fill them, but the two paint jobs did fill a lot of it in. No problems there yet, but not the correct way to do it really. Funny thing is the auto paint does not recommend the green etching primer for aluminum, but some other treatment. I have used it for some time with good success.