Re-Painting allumnimum

[Rick Hughes]

I have a chunky cast aluminum frame that is part of some marine watersports equipment. (link if you want to see it)

is the red seat frame that is the issue.

The 'paint' finish, has started flaking off in large pieces .. and aluminum underneath has some fine white oxide. this started at the through holes .........

Manufacturer advises this was powder coated ......... and obviously it is not very good after 2 yrs salt water use.

End of boating season I need to strip the finish off and re-finish .... manufacturer advised sandblasting & anodizing ......... however anodizing usually needs a lot of Hrs on polishing first (read - expensive) What options do I have ........ I could get the stuff sandblasted or chemically removed (might be kinder) .........

Anybody experience with acid etch primers & suitable paint ? .......... maybe even 2 part epoxy paint.

The item does not get any physical damage other than saltwater hitting it at

20mph when in use., it does get fully hosed down after each use.

Just an FYI ... the lower wings I had polished and anodized in red, and main bar in black ... they are fine.

[NT]

I've some limted experience with ali finishes, but not in a marine environment. From what I've seen, nothing is fully durable but anodising. You can anodise ali yourself, using clothes dye to colour it.

NT

[Rick Hughes]

I've some limted experience with ali finishes, but not in a marine environment. From what I've seen, nothing is fully durable but anodising. You can anodise ali yourself, using clothes dye to colour it.

I can get anodizing done locally ... the anodizing is cheap ... few pounds .. as they just add it to other work in same colour .... the cost is the polishing, and it would not be possible - within reason to polish this as surface will now have corrosion.

Wonder if I could get some etch primer, then re-powder coat ?

[Andy Dingley]

Powder coat sucks. It's OK if a piece is perfect and untouched, but any abrasion that goes through the coating just turns into a moist pocket that spreads under the coating.

I'd expect to use an etch primer and re-paint it myself, but I'd look for product advice from boat people, not landlubbers.

Anodising isn't a great finish for marine use. There's a lot of variation in anodising, between hard and soft anodises and in the basic quality of the work. Although I can anodise here (and in colour too, which is easy, even splash anodising) I wouldn't expect to do a good enough job to stand up to the marine environment. If you want to try it though, talk to Caswell about DIY kits. Their nickel plating is great stuff, if you're trying to do steel or brass.

[The Natural Philosopher]

+1

+1

Al. is poor material for marine use, full stop.

Id got for an epoxy paint as thick as possible..the cold non spraryed equivalent of powder coating. The anodising is simply a way to build a slightly thicker oxide layer, but oxide layers tend to be useless once scratched and in any case don't take well to salty spray. Regard anodising as a way to prep for coating - or as you say an etch primer. Or would epoxy type paint key to a simple sanded type surface?

I think if I had to use Al. on a sea going boat, I'd be off to a yachty place and looking for a tough expensive two pack paint...and some advice on how to prep the surface..

[Andy Dingley]

Having now looked at the photo, this seems like a simple enough shape that you can polish it yourself. Anodisers will take this, at much less cost, if it's already polished or part-polished. You need an angle grinder and a few paint stripping disks (they look like plastic scourers). These ought to do it, although you _might_need a fine flap wheel to start if the powder coat is particularly tough.

Once the aluminium is stripped clean, then polish it. Use an electric drill and a range of wire brushes with abrasive-filled red nylon bristles. These give a good polish on aluminium. There are also a range of disks from 3M specially for stripping paint and polishing aluminium. If you want a mirror finish (which isn't necessarily a good idea) then finsih with 3M / Webrax scourer pads or else Garryflex rubber blocks. Really though, take it to the plastic abrasive wheel stage, then hand it over to the anodiser for final polishing (one stage is cheap).

As for any polishing, it's not about the shine, it's about taking the coarse scratches out. Don't move to a finer grit until you're really done with the coarse stuff.

_Don't_ use steel tools, or tools you've also used on steel.

[Rick Hughes]

Powder coat sucks. It's OK if a piece is perfect and untouched, but any abrasion that goes through the coating just turns into a moist pocket that spreads under the coating.

Exactly what happend ... from the though holes I could see a bubble starting when they become about 3" across they slit, and start flaking.

I'd expect to use an etch primer and re-paint it myself, but I'd look for product advice from boat people, not landlubbers.

:-)

I went to a professional anodizing company, it came out a sperb jobg on the foil ... but it discolours almost as soon as it gets in contact with salt water.

[Rick Hughes]

wonderred how long before it arrived ....(rminds me must get mione back form mate who borrowed it for the weekend, in May)

Thanks for other comments

[Andy Champ]

Any of you guys ever look at a boat's mast? 9 out of 10 are anodized aluminium alloys. (the rest are either wood or synthetic composites such as carbon/epoxy)

Andy

[Rick Hughes]

My experience with anodizing is not good on red that is for sure, been re-anodized twice, it fades to pink within 2 -3 weeks. That is about 2 Hrs in salt water .. rest of time, rinsed, dried & kept out of the sun.

[Rick Hughes]

An update ... from a Powder Coating specialist company ... " It appears your item had Powder coat applied to insufficiently prepared surface. We would do this by grit blasting with aluminum oxide to provide a suitably abraded surface, then apply a suitable etch /primer baked on fully, before being followed by the powder coated finish.

[Andy Dingley]

It's a great finish if it's done right, but this usually means careful factory anodising immediately after extrusion of sections, where it's a repeat process day-in day-out on the same sections and alloys. Post- fabrication anodising by plating shops is a real crap-shoot for quality and longevity.