Author Topic: Finishing question - clear coating onto smooth aluminium  (Read 534 times)

jimladladlooklike

Finishing question - clear coating onto smooth aluminium
« on: February 16, 2021, 05:14:46 AM »
Hey

So I went n dry sanded a few 1590x enclosures, going up to 1200 grit. They looked and felt smooth enough for me so I then went about printing onto them in an unorthodox way using a lino print my partner made and some different coloured printing (acrylic?) inks she kindly sacrificed. I was super happy with the resulting effect. It gave a beautiful textured look and hardened off after an at roasting temperature. I then wanted to protect the design with a clear coat, which worked better than I'd expected when using a matt clear coat.

However, I ran into trouble when attempting the same with polyurethane. I applied two thin coats onto the enclosures, leaving 30 mins in between and then left for over 24 hours. But, when I started adding hardware I started getting cracks in the finish. Gutted! They looked killer. Soo now I've sanded them back to bare metal again and now I'm looking for some advice on how to retain some of the sheen of the sanded aluminium whilst being as tough as possible.

stallik

Re: Finishing question - clear coating onto smooth aluminium
« Reply #1 on: February 16, 2021, 05:20:19 AM »
Sounds like the poly finish has reacted with the acrylic. Id test some acrylic lacquer over your colour before refinishing the enclosure.
Insanity: doing the same thing over and over again and expecting different results. Albert Einstein

jimladladlooklike

Re: Finishing question - clear coating onto smooth aluminium
« Reply #2 on: February 16, 2021, 06:57:41 AM »
So the design/print only took up a v small space, the rest was left bare and that's where the problems occurred. Still, will try acrylic lacquer. Thanks!

stallik

Re: Finishing question - clear coating onto smooth aluminium
« Reply #3 on: February 16, 2021, 07:04:51 AM »
Ah, plain ally is more difficult. I normally use an etch primer but just lacquer? Had difficulties with this in the past. Ill try some acrylic myself. Maybe someone will chime in and put us both right?
Insanity: doing the same thing over and over again and expecting different results. Albert Einstein

amptramp

Re: Finishing question - clear coating onto smooth aluminium
« Reply #4 on: February 16, 2021, 09:04:32 AM »
You can put enamel over lacquer but not necessarily the other way around.  I would suggest if you use a lacquer base, you should use a lacquer top coat but if you use an enamel base, use an enamel top coat from the same family of paints.

kaycee

Re: Finishing question - clear coating onto smooth aluminium
« Reply #5 on: February 16, 2021, 09:35:43 AM »
The top coat needs something to key onto, by polishing it, you've removed that key. Also, the alu on these boxes is a pretty dirty metal which makes it worse. I have tried in the past and had the same crazing. You might try an automotive lacquer, an engine VHT brand made to go onto bare metal, but that stuff often yellows. Maybe no labels and regular polishing.

vigilante397

Re: Finishing question - clear coating onto smooth aluminium
« Reply #6 on: February 16, 2021, 09:38:53 AM »
I do clear powdercoat over bare aluminum all the time, turns out great.
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Bunkey

Re: Finishing question - clear coating onto smooth aluminium
« Reply #7 on: February 16, 2021, 09:51:03 AM »
I've used PU laquer on dished alloy wheels before..

Generally you would use an etch primer to help with adhesion on galvanised or alloy metals like stallik said but in this case you'd be best leaving the alloy surface quite rough to get the laquer to key into that surface. The smooth finish of the lacquer itself will give the same final appearance as if the aluminium underneath was smooth.

If I did the wheels again I'd probably forgo the lacquer, polish the alloy to the desired finish and wax the whole thing for protection - Sure it's not quite as hard wearing and might benefit from being reapplied at some point in the future depending how it gets handled - it'll give a nice soft sheen finish to both the metal and the graphic though, as long as the graphic is hard wearing enough to endure the wax application.

Couple of options there anyway.. Try a 220grit or maybe even <180 and see how the lacquer takes.

tonyharker

Re: Finishing question - clear coating onto smooth aluminium
« Reply #8 on: February 16, 2021, 10:38:49 AM »
Clear etch primer for aluminium is available.

stallik

Re: Finishing question - clear coating onto smooth aluminium
« Reply #9 on: February 16, 2021, 12:04:26 PM »
Tried my acrylic lacquer straight onto the ally. Looks great but scratches straight off!
I see that clear etch primers are available..
« Last Edit: February 16, 2021, 12:07:51 PM by stallik »
Insanity: doing the same thing over and over again and expecting different results. Albert Einstein

jimladladlooklike

Re: Finishing question - clear coating onto smooth aluminium
« Reply #10 on: February 17, 2021, 06:26:09 AM »
Tried my acrylic lacquer straight onto the ally. Looks great but scratches straight off!
I see that clear etch primers are available..

Glad it wasn't just me doing it wrong! I appreciate the time you took to test it out, thanks.

Gonna give clear etch primer a go, followed by some clear gloss acrylic based paint of some kind.

Cheers for all your help guys

davent

Re: Finishing question - clear coating onto smooth aluminium
« Reply #11 on: February 17, 2021, 12:37:23 PM »
So far not having much luck finding clear self etching primer for aluminum but have come across products like this that are said to protect polished aluminum, used for polished aluminum rims and the like.

https://www.shineseal.com/
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kaycee

Re: Finishing question - clear coating onto smooth aluminium
« Reply #12 on: February 17, 2021, 12:48:59 PM »
Ceramic polish might be worth a try? Has worked well keeping the shine on the polished alu on my old RD250 motorbike. May dissolve your lettering,so test first.

duck_arse

Re: Finishing question - clear coating onto smooth aluminium
« Reply #13 on: February 18, 2021, 09:27:29 AM »
Ceramic polish might be worth a try? Has worked well keeping the shine on the polished alu on my old RD250 motorbike. May dissolve your lettering,so test first.

ohhh - what model RD?
"I think we're done here."

yyz_2112

Re: Finishing question - clear coating onto smooth aluminium
« Reply #14 on: February 18, 2021, 09:30:41 AM »
Your polyurethane was too soft. It takes up to 30 days to cure depending on the surface and the coating thickness. Urethane does truly cure unlike most lacquers which simply outgas. All that being said, any metal will need a bonding primer before being coated with polyurethane, be it solvent based or waterborne. Rustoleum makes decent and readily available products for this purpose.

kaycee

Re: Finishing question - clear coating onto smooth aluminium
« Reply #15 on: February 18, 2021, 03:52:06 PM »
Ceramic polish might be worth a try? Has worked well keeping the shine on the polished alu on my old RD250 motorbike. May dissolve your lettering,so test first.

ohhh - what model RD?

Mine is the one in front, 'The Precious' as the wife calls her.



1979 UK 250E, last of the Yamaha aircooled two-stroke twins. CDI ignition, revised port timings, worse brakes. The US market got the handsome Daytona Special instead (also Canada and Australasia). The Blue 400C behind is my mate Mick's, its an American model imported (smaller tank, high rise bars).

I got it about 3 years ago, it had done about 200 miles in the last 20 years, I put 3000 on it that summer! - what a blast! It just ran and ran as I fine tuned it and the knowledge seeped back into the front of my brain from decades ago. I would have liked a Kawasaki  triple as I mostly rode those back in the day, but the prices were out of my reach - I had Yamaha's too though, a 72 YR5 350 and the watercooled RD350LC, my last ride at the end of the 80's when the gang all got married or moved away and it wasn't fun any more.

At last Summers' Aircooled Club Rally on an 80 mile ride out of the villages around Darby.



You a Smoker DA?


duck_arse

Re: Finishing question - clear coating onto smooth aluminium
« Reply #16 on: February 19, 2021, 09:43:59 AM »
was, and you'll larff - I had the only RD250F in New South Wales. second last air-cooled model here, the F and G tanks were the same, different stripes. mine looked like a skateboard.



I was the world's worst rider. haven't ridden since the mid eighties - cops didn't want me to. clip-ons, half rear-sets [watch that first to second change!], chambers, air filters, ports, P plate ....
"I think we're done here."

kaycee

Re: Finishing question - clear coating onto smooth aluminium
« Reply #17 on: February 19, 2021, 11:31:51 AM »
Definately a kindered spirit then  8)

Yes, I know which model you had, a very handsome bike. They are probably the most difficult to get parts for now due to the limited run of production. Dealers have been importing container loads of RD's from US scrap yards for the last few years to feed the UK market, but they must be getting to the bottom of the barrel now as most of the recent ones look like they belonged to SpongeBob!

I have a mate who has his actual, old 250B. When he stopped riding he put it in the back of his mums garage and then got it out to re commission it decades later.

I have a set of 350 barrels to stick on mine when I can locate some Pistons for them.