Painting old portlight aluminium

[FairweatherDave]

I have searched various threads on painting aluminium and I am still confused. I am "restoring" my Centaur portlights and there is some corrosion in places. However I have parts of aluminium which seem pretty good. I am not sure what anodised means technically but I presume the good bits are where the anodising has remained intact. Should I do a thorough rub down/plus boiling water then use etching primer and paint all the aluminium, internal and exterior surfaces OR should I only paint the internal aluminium and leave the external bits to the elements? Does a "thorough rub down" damage the anodising on the significant areas that have not corroded?

I want to hand paint/do the job as cheaply as possible but paint recommendations would be useful. I have the etching primer ((U-pol Acid #8) but was shocked at the price of hammerite (smooth) and enamel so thought I'd get advice here. Many thanks for any contributions.

 

[martinaskey]

I had a similar problem with the portlight on my boat - corroding and seals failing
Decided to take a risk and restore it myself.
I took the unit out of the boat and completely disassembled it.
Removed the old, hardened seal. cleaned with meths and lightly sanded the aluminuim back to a fine surface all over (600grit).
I decided not to worry about damaging the anodising too much (although I didn't go mad with the sanding) because the anodising is just an extra thick layer of the oxide that naturally forms and I intended to paint anyhow (decided that sending the unit for reanodising would cost too much).
Primed with hammerite primer and resprayed with matt hammerite on all surfaces inside and out except the mating faces of the hinges.
Replaced seal and reinstalled.
That was 18 months ago and it still looks like new so I'm happy enough.

Martin

 

[VicS]

I have searched various threads on painting aluminium and I am still confused. I am "restoring" my Centaur portlights and there is some corrosion in places. However I have parts of aluminium which seem pretty good. I am not sure what anodised means technically but I presume the good bits are where the anodising has remained intact. Should I do a thorough rub down/plus boiling water then use etching primer and paint all the aluminium, internal and exterior surfaces OR should I only paint the internal aluminium and leave the external bits to the elements? Does a "thorough rub down" damage the anodising on the significant areas that have not corroded?

I want to hand paint/do the job as cheaply as possible but paint recommendations would be useful. I have the etching primer ((U-pol Acid #8) but was shocked at the price of hammerite (smooth) and enamel so thought I'd get advice here. Many thanks for any contributions.

Anodised means that the surface has a protective oxide film. Anodising is done electrolytically in a sulphuric acid bath. The oxide layer can be coloured if required for decorative purposes

The "painted" portholes are probably not in fact anodised although the bright unpainted ones will be

A few years ago I got a couple of Westerly port holes re-coated by our paint technologists at work. IIRC they were grit blasted, with a soft grit to avoid removing too much metal, They were then etch-primed and finally painted with chlorinated rubber paint.

I must remember to look at the boat ( it belonged to a friend and now belongs to his son) to see how they have stood the test of time

The secret is I think to remove all the corrosion by grit blasting and to apply the primer immediately

 

[Norman_E]

Anodising is a process very similar to electo plating, in which the very thin oxide layer that naturally forms on aluminium is enhanced and coloured to form a tough protective layer. Wikipedia explains it well. http://en.wikipedia.org/wiki/Anodizing
If you rub it down you will damage or remove any anodising that is left. In my experience the only things to do with aluminium parts that have damaged anodising are to touch them up with aluminium paint after cleaning them with hot water, but not using any abrasives; or to remove the item, abrade away all the existing anodising and have it redone. You can even get kits to do it yourself.

 

[Nicholas123]

If you hav'nt got a grit blaster available you might try a wire brush

 

[FairweatherDave]

Thanks all so far.Martin, I think your approach summarises my plan. I do have the units out. My reservation is using paint on the external exposed surfaces and creating a new regular maintenance job. The seals and sealant bit I can understand need doing (the portlights weren't leaking but had to be extracted to do the headlining properly).
So any recommendations for suitable metal paint that can handle the environment? Alternatives to Hammerite?

 

[martinaskey]

Has to be said that I like Hammerite (I don't work for them !!)
It seems to do the job at a sensible price without specialist preparation.
On a previous boat I painted a boom in white hammerite to match a white alloy mast. This was also successful and retained coating integrity although over 4 or 5 years the odd chip / scratch appeared from impacts in winter storage !
Good preparation is the most important bit - cleaning, sanding, priming, resanding, repriming, cleaning, sanding, cleaning ...............
I used their 'special metals' primer.
Suspect there are better professional products but in the 'available at B&Q' range this seems to work !
M

 

[Gordonmc]

Assuming the portlights will be removed from the boat you might consider having them powder-coated.
I had an aluminium windlass done by a local (to me) company which specialises in re-finishing boy racer alloy wheels. They offered a choice of colours including clear and did a good job at reasonable cost.
There may be somewhere closer to you doing similar.

 

[Bodach na mara]

Assuming the portlights will be removed from the boat you might consider having them powder-coated.
I had an aluminium windlass done by a local (to me) company which specialises in re-finishing boy racer alloy wheels. They offered a choice of colours including clear and did a good job at reasonable cost.
There may be somewhere closer to you doing similar.

Sorry Gordon, but my experience with powder coating is rather different. I got second hand windows that had been powder coated and had to remove it because it was flaking off in large bits. I also have a Vetus hydraulic steering pump that I did not need to make any effort to remove the powder coating. It all fell off within two years. The windows were painted with hammerite smooth and the steering pump with Adli metal paint.