Cleaning aluminium for painting.

[Scary Des]

I have had a major problem with the paint on my outdrive, basically the top coats didn’t agree with the bottom and all feel off So I have stripped it back to bare metal where I can get a grinder brush to it. However there are still one or two areas where I can’t get the brush and I was wondering if anyone can recommend a method of getting these areas clean paints all gone but there is still surface corrosion so something like a spray-on acid might be good Des

[Neville]

single pack chromate free etch primer available in spray can form from your local motor factor shop. - there is only one perfect answer when there is corrosion - remove it! not always that easy...

[Scary Des]

Originally Posted by Neville

single pack chromate free etch primer .....

That is what I had before but maybe I used it wrong. What would you over paint with? Des

[Pete7]

Des, I used the two pack stuff on bare Ali, really odd stuff thinner than water which dries as you paint it on so it sturn to an evo stick consistency. That was followed by a couple of coats of paint and finally antifouling paint. I followed the International guide. It wasn't particulalry cheap but seems to have lasted well, except the prop which it quickly peeled off so I now only use antifoul on that and change the prop with the spare during the season.

Pete

[Scary Des]

I was going to use the etch primer but when I asked international what I should do they suggested a different primer I think I’ll give them another call Des

[Neville]

des, the single pack does have a tendency to react with some paints especially if it is put on too thickly. I would normally put on a single pack polyurethane paint on top or a boot top.

It is an idea to clean the surface well that it is going on to with hot water and soap, finishing off with a panel wipe.

One problem with some two packs is that they need to go on at a milder temperature, and if it is too cold they dont 'etch' this is noticed by the change or non change in colour - brown / yellow.

If you are wanting to do it properly, two packs are the answer as they are much more durable.

Alot of outboard people use the cheap single pack chromate free spray and then put on a cellulose top coat which is available from halfords etc. Sounds a bit cheap !

[Scary Des]

International are suggesting I should use Interprotect because etching is difficult to use and that if you abrade the surface with sand paper you get the same effect as etching Now I’m confused Des

[Neville]

des, normally you would use etching on bare metals such as aluminium because they are 'shiney' and not much stciks to them even when sanded down. The aluminium just gets smoother and the paint just flakes off.

Thats where etch primer comes in. But etch primer is just really a very thin barrier coat and all it does is help the next coat adhere to the bare metal. It doesnt offer any protection as such.

Interprotect is an epoxy based primer and can be used over more bases with good effect. Again it is subject to the correct conditions - temperature, but you can apply it on top of bare metal or painted surfaces. Epoxy primers are not 'etching' but the stck like turds do to a blanket. Epoxy is the most durable coating / adhesive known.

For bare aluminium it is a toss up between an etch primer or say an epoxy primer. If it is a small job i would probably use an etch primer. Alot cheaper aswell.

[Matt]

Have a look at this:
http://www.mercurymarine.com/technic...tion_faqs#1135

[Neville]

I think if i was going to that length i would pull the drive off and gritblast it properly. You will have to cross reference the paints as they are all USA brands, I dont think that i have ever seen them here. But that is alongthe lines of what we have been talking about here. Main thing is to get the surfaces as clean as possible and free from corrosion, dirt and lose stuff.

The only way to do that in my opinion is to strip the drive off the transom which is quite a job, and then remove the transom assembly. There are lots of places that you cannot get in to on a sternpowr unit unless you strip it.

Suggest you spend the next few years planning !