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 !

[Scary Des]

Originally Posted by Neville

I think if i was going to that length i would pull the drive off..............

I’ve taken it off and stripped it back to bare metal nearly everywhere, but it is some places, like the ram pockets, that are virtually impossible to get to. I’m probably just being lazy but I was hoping for something like a paint stripper that you wipe on and it leaves a shiny finish.
Neville do you have any cork transom gaskets or an external transom hose set, I really loath having to pay Lancing prices. Des

[jwalker]

Good one, Matt.


The problem with alli is that you are not painting the alli because it reacts with the oxygen in the air instantly. Hence the use of etch primer. However, I've had eff all success with etch primer on outboards. If you don't go with the International or Mercury method here's an idea which I am going to try the next time I need to do the job. It's based on a way to solder aluminium so, since you're tecki folk, you're gonna get that bit first.

Aluminium can be soldered using a normal soldering iron and solder. Give the surface a sanding and immediately cover it with gear oil to exclude the air . Solder through the oil with a scraping action. As the aluminium is scraped by the iron tip, the solder with adhere because there is no oxygen present at the surface. The reason for using gear oil is that it has a goodly quantity of anti-oxidant present in it.

Now, it occured to me that if I cleaned back the aluminium and immediately applied paint and then abraded through the wet paint, it may have a half decent chance of sticking to real aluminium.

Just an idea.

[Neville]

JW : The only problem i could see in doing that would be the time taken to clean the oil off, and keeping the surface clean with all that stuff around.

Ive found the only good method is to put the parts in to be beadblasted or grit balsted which leaves a really good mechanical key, and thenive not found much difference in which paint system i used.

Des : I will PM you with an dress to go to in the states for new parts, they beat the hell out of lancing. As for the gaskets, i now use a neporene gasket which we make up ourselves. I found the cork ones prone to leaks on a couple of boats last year, and have since tried using different methods. The last couple i have done have been with a polysuphide sealant on the main face andthen a polyurethane sealer fillet around the outside. That was a method pointed out to me by a company that refurbished sternpowr units a few years ago for the mod.

[Neville]

The places to check for cleanness are the penetrators for the hydraulics on the transom assembly, they get dirty and the o rings harden, and as you may have found out the ram bases get corroded. The drives are quite sturdy and a little bit of loose paint wont do them any harm, but bad anodes will!

[jwalker]

Originally Posted by Neville

JW : The only problem i could see in doing that would be the time taken to clean the oil off, and keeping the surface clean with all that stuff around.

Neville, you misunderstand, perhaps I didn't make it clear. The plan was to use the paint to exclude the air. The oil is only used for the soldering process.

[Scary Des]

JW I understand what you are saying, bloody tricky but I sure you could do it.
Could you use an oil based paint and its base oil instead of gear oil that way you would not need to clean the surface much before painting

What really surprises me is how confident International are that you only have to sand then paint Des

[Scary Des]

Originally Posted by Scary Des

JW I understand what you are saying....................

Ooops I obviously didn’t understand what you were saying but now I do will the paint draw the O2 away or isn’t that an issue? Des

[Scary Des]

Originally Posted by Neville

........... i now use a neporene gasket which we make up ourselves..........

Interesting, what grade and thickness
and what do you mean by the penetrators
thanks Des

[Jono]

We have developed a sure-fire way of dealing with problems like this with Ali or any of the "exotics".......
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.....give it to some other poor bugger to do...

[jwalker]

Originally Posted by Scary Des

Interesting, what grade and thickness
and what do you mean by the penetrators
thanks Des

I've used hypalon and it's been in place, in diesel fuel, for a couple of years. Seems ok. Just a thought incase you happen to have a bit lying around.