Painting Aluminium

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whisper

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Hoping to get a slightly battered aluminium dinghy in the near future. Would like to smarten it up and paint the hull - any special pre-cleaning/ painting methods/ paints etc that I should know about?
Thanks.
 
You'll need an etch primer as Davidnnnn says followed by the primer for your chosen paint system. However the job will only ever be as good as the preparation. Low pressure grit blasting with aluminium oxide would be the best and probably the only practical method.

Check the paint manufacturers websites for all the details. Eg International yachtpaints at www.yachtpaint.com/uk

IMHO your best bet will be to leave it unpainted but make sure nothing made of copper or its alloys is left in it.
 
You need to cut the surface back to totally clean metal and then use a two pack Zinc Chromate primer which will etch the surface. This is the stuff used on aluminium street lamps as well as outboards by the manufacturers during production.

Don't use a two pack enamel as the finish coat however, as this will in time harden and with a soft metal like sheet aluminium a certain amount of flexibility is desirable. Two pack finish is fine for outboard castings.

Steve Cronin
 
I agree with Vic re just leaving the aluminium un-painted - unlike steel, aluminium does not need paint to stop corrosion - it will survive very happily with its own protective oxide layer on the surface.
And if you paint it nicely, then not only will it cost a bit, but then it is much more likely that some barsteward will be tempted to pinch it....... whereas no self respecting boat thief will want to be seen dead in a tatty old un-painted dinghy!

The ally cat in the photo on the left has un-painted topsides - she was built 6 years ago, and the aluminium has now gone a nice uniform dull grey colour, which is much easier to look after than a paint job.
 
Have just repaired the broken mast heel on my boat, and was actually going to post about what primer and paint to use.
I take it, I will need to use the zinc chromate primer, but want to paint it black, what paint would be recomended? hopefully I can get a small amount and where from?
Cheers, Eamonn.
 
See my other post yesterday for general painting tips but add the following for aluminium.

Aluminium is quite weird stuff to paint because it oxidises immediately meaning your regular paints and primers attach to the oxidisation not the surface, as soon as your paint fully dries out it will fall off.

Chrome etch primer cuts through the oxidisation and only acts to key to the surface, meaning you will need to put a regular primer on top of this. Don’t think that because off the etching action you don’t need to Rub the surface down and remove the old oxidisation. I presume this stuff is still a two pack material remember to mix the contents together as per the instructions. If it says stir well it does mean stir well, and here its needed more so to get all the chemicals mixed together.

In my day this stuff once mixed did not retain its ability to etch through oxidisation so only mix up what you need for the actual job for the day. Do not put several coats on, two light coats will suffice, unlike regular primer you are not giving yourself a flatter surface or building up, you are only providing a key coat for the primer.

Once applied do not rub down as you will go through the etch and ruin the effects.

I always sprayed this stuff on large areas, if it was for a small area I used to sponge it on, literally dipping a sponge in and patting it all over the surface.

If you do spray remember to use a face mask and protect the other areas by masking off for a few feet all around the area.

After etching with chrome etch do not under any circumstances apply the regular primer until you are sure the chrome etch is dry.

I always applied six coats of primer on top of aluminium because when it came to wet flatting (go easy and don’t use anything more abrasive than 150) I did not want to go through the etching primer. If you do go through anywhere, mix up another fresh batch and stipple on with a sponge again until the area is re etched.

Don’t be tempted to put loads of top coats on for the final finish because this could end up being brittle and as the surface is aluminium you will need a material that will flex with the pained surface, epoxies tend to be brittle and will therefore end up flaking off later.

Lastly If I wanted t make a small area look attractive and yet not divert attention from fancy paint elsewhere I always went for satin Black, very functional easy to cover and hides all your mistakes.

Lastly I agree that you don’t need to re paint an aluminium boat, I like it when they get old and the aluminium shows through, if you want to clean it up just get a scouring cloth and give it the once over every now and again.
 
Yes I Agree with the scouring cloth / Scotch pad & not painting Aluminium Dinghy's / Boats
Being in the ally boatbuilding trade, Thanks to incompetent_crew for the detailed method plan for painting.
one trick I have found is to use Draper Ink & Gum remover with a scouring cloth & plenty of elbow grease, This actually takes a layer off and polishes up to a shine, you need plenty of Draper Ink & Gum remover though !!!

New to Alloy boatbuilding

www.robustboats.co.uk
 
I have a painted mast (black). I recently repainted it using smooth Hammerite after touching up the small bare patches of aluminium with Hammerite primer for non- ferrous metals. It's still there 2 years later. The only slight problem perhaps with your mast heel is that Hammerite goes on quite thick.
 
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