Painting an Aluminium Chassis

[cpsmusic]

Hi All,

Finally getting round to finishing a Bassman Head-style project that's been sitting idle for a while.

The amp's chassis is aluminium and I was originally going to leave it bare, but I'm now thinking that it might look better painted.

Am I right in thinking that a gloss epoxy would be the most suitable sort of paint for this task? Something like this:

Wattyl Killrust Epoxy Gloss Enamel Paint, Black - 300g

Cheers!

 

[k brown]

May not be the esthetic you're after, but other than powder coating, the most durable paint finish I've found for alum chassis is high quality bare metal primer followed by wrinkle-paint (taking care to apply properly), followed by a couple of clear coats of water-based polyurethane.

Glossy finishes look nice, but show scratcehs more easily.

 

[cpsmusic]

May not be the esthetic you're after, but other than powder coating, the most durable paint finish I've found for alum chassis is high quality bare metal primer followed by wrinkle-paint (taking care to apply properly), followed by a couple of clear coats of water-based polyurethane.

Glossy finishes look nice, but show scratcehs more easily.

At this stage I just want to get the thing finished lol

I'm wondering now about matte vs gloss - any thoughts?

 

[k brown]

Personally, over wrinkle, I'd do satin.

 

[Rob Flinn]

if you're painting I would use an etch primer first on aluminium.

 

[k brown]

if you're painting I would use an etch primer first on aluminium.

Yes, and sanding first.

 

[MicMaven]

May not be the esthetic you're after, but other than powder coating, the most durable paint finish I've found for alum chassis is high quality bare metal primer followed by wrinkle-paint (taking care to apply properly), followed by a couple of clear coats of water-based polyurethane.

Glossy finishes look nice, but show scratcehs more easily.

I agree. Sometimes that sort of paint is called "hammered" finish. It looks good, and (as (Mr. K Brown says) minimizes scratches more than a glossy finish.

SERVING SUGGESTION - After allowing enamel or hammered paint to dry normally (at least two days) - I heat the item with a heat gun - some guys bake it in an oven at 450 degrees F (230 C) and when it really hot, I drop it into a pot of really cold water to harden the paint more than normal drying time allows. I learned this trick from ham radio operators who restore Morse Code key bases and other equipment, such as repainting metal receiver cabinets. The hammered finish works best with this heat treatment.​

I did this restoring a cheap ($30) Behringer C-1 body with dark bronze hammered paint, and with an even cheaper ($19) CAD GXL-1800 body using dark red enamel spray paint. (See dual-before-and-after images below.)

DO NOT BE IN A HURRY -- I realize waiting even one extra day seems like an eternity when one is chomping at the bit to finish a new microphone project! But, haste makes waste, and it is surely worth an extra day or two to assure your new paint job is durable and long-lasting. You may be looking at it for a very long time! ​

Good luck. James /K8JHR

 

[k brown]

I agree. Sometimes that sort of paint is called "hammered" finish. It looks good, and (as (Mr. K Brown says) minimizes scratches more than a glossy finish.

SERVING SUGGESTION - After allowing enamel or hammered paint to dry normally (at least two days) - I heat the item with a heat gun - some guys bake it in an oven at 450 degrees F (230 C) and when it really hot, I drop it into a pot of really cold water to harden the paint more than normal drying time allows. I learned this trick from ham radio operators who restore Morse Code key bases and other equipment, such as repainting metal receiver cabinets. The hammered finish works best with this heat treatment.​

I did this restoring a cheap ($30) Behringer C-1 body with dark bronze hammered paint, and with an even cheaper ($19) CAD GXL-1800 body using dark red enamel spray paint. (See dual-before-and-after images below.)

DO NOT BE IN A HURRY -- I realize waiting even one extra day seems like an eternity when one is chomping at the bit to finish a new microphone project! But, haste makes waste, and it is surely worth an extra day or two to assure your new paint job is durable and long-lasting. You may be looking at it for a very long time! ​

Good luck. James /K8JHR

View attachment 116325View attachment 116327View attachment 116328

No, Wrinkle paint and 'hammertone' are two completely different paints and 'looks'. Wrinkle paint has a 'shriveled' look, and is deeply textured which makes it resistant to scratches. It was used a lot for industrial and military equipment in the 40s and 50s. It's also the trickiest to do properly, but it's great for gear that gets rough treatment.

Hammertone mimics the appearence of peen-hammered metal, and has a swirly, metallic pattern, but is just as smooth as any gloss finish, and therefore scratches just as easily. None of your photos look like hammertone to me - just metalflake.

 

[Gold]

Are there any tricks for making wrinkle paint more wrinkly when using rattle can paint? When I try it with Rusoleum it never looks as textured as I think it should.

 

[k brown]

Are there any tricks for making wrinkle paint more wrinkly when using rattle can paint? When I try it with Rusoleum it never looks as textured as I think it should.

Here's a tip:
https://www.diyaudio.com/community/threads/vintage-wrinkle-paint-finish.390726/

 

[cpsmusic]

Yes, and sanding first.

What grit would you recommend?

 

[k brown]

What grit would you recommend?

100 progressing to 400.

 

[RoadrunnerOZ]

Here's a tip:
https://www.diyaudio.com/community/threads/vintage-wrinkle-paint-finish.390726/

Are there any tricks for making wrinkle paint more wrinkly when using rattle can paint? When I try it with Rusoleum it never looks as textured as I think it should.

As mentioned in the post above the second and third coats are applied after 5 minutes - literally as soon as the paint skins off once another coat is applied this causes the first coat to wrinkle and so on with subsequent coats. It is important to get a thick coat first up so as to get a full wrinkle happening. The following coats can be thinner applied between 5 and 10 minutes after the preceding coat.
I spent 5 years working for a company that did specialist factory restoration of luxury Supercars and some of the Ferrari engine covers are wrinkle finish red. We used high temperature wrinkle paints and as soon as the last coat was applied these were put into our heat booth to wrinkle up. If any coat is still fully wet when the next coat goes on it won’t wrinkle properly, you need the surface skin to start the process (this can happen slightly differently with normal paint processes - it’s called orange peel). You need at least 80-100degC for a proper cure - a domestic oven which is fan forced can work but you need to be sure the paint has skinned sufficiently to prevent air forced runs.
Most important the metal must be cleaned with a degreaser and lint free cloth - the degreaser we used was isopropyl and all handling was with nitrile gloves also wiped with an isopropyl soaked cloth - any fingerprints will cause blotches.
There is a range of wrinkle paints like VHT Wrinkle Plus and so on - each will have its own optimum cure temp - we ran the heat booth oven at 95degC with excellent results - this was preheated well beforehand as it was large enough to fit a car into. You can also use IR lamps but you need the heat to get to all surfaces to properly wrinkle.
https://www.vhtpaint.com/high-heat/vht-wrinkle-plus-coatings
Hammer finish is a completely different process and paint - this is like exaggerated orange peel with a high or satin gloss finish. Used in a lot of vintage transformer and relay housings they require the same cleaning and handling precautions as above and depending on the brand may require an etch primer for aluminium or be self priming.
Good paint adhesion will be better achieved with pre-dressing the surface using a fine Scotchbrite pad then cleaning.

 

[scott2000]

None of your photos look like hammertone to me

Enlarge them..... It's tight but you can make out the dimples and fish eye looking deals...

Is that the baking process that makes it so unique??

 

[RoadrunnerOZ]

The ingredients in the hammer finish paint create the finish - suspended aluminium particles orient differently to create the effect aided by minute quantities of silicone oil - the thicker the initial coats the better the hammer and the larger the pattern - there needs to be room within the layer for the particles to stand upright in some areas. Too thin a first coat will result in tiny hammer finish. The trick is to get enough paint on the surface without it running - a medium coat first followed a few minutes later with a thicker second coat will allow enough depth of paint for the finish to appear. Slow even spray application is the key - try a bit of metal as a tester first - ambient temperature can affect the results. Crosshatch application ensures even coverage.

 

[metalockpick]

No, Wrinkle paint and 'hammertone' are two completely different paints and 'looks'. Wrinkle paint has a 'shriveled' look, and is deeply textured which makes it resistant to scratches. It was used a lot for industrial and military equipment in the 40s and 50s. It's also the trickiest to do properly, but it's great for gear that gets rough treatment.

Hammertone mimics the appearence of peen-hammered metal, and has a swirly, metallic pattern, but is just as smooth as any gloss finish, and therefore scratches just as easily. None of your photos look like hammertone to me - just metalflake.

Wrinkle paint likes a heat gun treatment while it's tacky, which can help with making the wrinkling even.

 

[RoadrunnerOZ]

It won’t wrinkle properly without the correct heat - some areas may and some won’t - it’s normally not a cold cure product. It’s also incredibly tough. When painting the work should be done on a tray with standoffs that can go into the oven - any handling of the paint will leave finger impressions in the paint. An oven guarantees uniform heating and therefore finish. A heat gun can work but you have to keep at it until the whole surface has wrinkled evenly and also being careful not to burn the uncured paint - it goes brown.

 

[RoadrunnerOZ]

100 progressing to 400.

Finishing with Mirlon or Scotchbrite afterwards ensures any shiny bits left after sanding (the bits left untouched between the grits - you need a surface microscope to see this) are scuffed. We used Mirlon as a final surface prep in the paint shop on alloy and steel panels before priming and also between coats of primer (if required) base-coat and clear - reduces pinholes in the paint incredibly. Wet sanding is more effective than dry. If blowing off using compressed air from a compressor the air needs to be oil free or you get massive pinholes everywhere - safer for small jobs to used canned air used for camera cleaning.

 

[Gold]

Thanks RoadrunnerOZ! That is excellent information. I want to do a nice job on some Hammond 1588 aluminum project boxes. I have a really good citrus oil degreaser made by Loctite, IPA and acetone. I have scotchbrite and fine stainless brushes. I have a heat gun and an infared thermometer. Now all I need is patience.

 

[RoadrunnerOZ]

Thanks RoadrunnerOZ! That is excellent information. I want to do a nice job on some Hamilton 1588 aluminum project boxes. I have a really good citrus oil degreaser made by Loctite, IPA and acetone. I have scotchbrite and fine stainless brushes. I have a heat gun and an infared thermometer. Now all I need is patience.

You can get lint free paint prep wiping cloths that are designed for paint prep - any auto store that carries a range of paints for cars should have these cloths. They’re like a paper towel but tougher. The Mirlon comes in various grades as well plus including pads for orbital and rotary sander/buffers. Worth checking out.
Edit: any oil based degreasers still need to be washed off before painting. We used gun wash thinners then isopropyl for stubborn stuff but 99.9% iso is always the last product in the chain. The lint free cloths prevent any microscopic fibre particles creating a blister in the paint and filtered compressed air blow down to prevent dust particles causing pinholes.
When you paint a $600,000 car you have to be sure it is done right - we did paint thickness to factory standards in microns, which means you have to get it right first time or sand it all down and start again. Paint thickness gauges were used all the time to check job finish - primer, base coat and clear coat. We did a lot of restoration to “factory or better” and this required in some cases replicating paint jobs of 70 or more years ago. The old Rolls Royce and Bentley relays had the green or silver grey hammer finish casings as well as some of the other engine bay housings like wiper motors and fluid tanks and even air filter housings - these had to be matched, stripped and repainted exactly to original. Lot of work but very satisfying. I remember matching a satin black paint finish on engine bay side trims in a Lotus and used a matte black plastic dye mixed with semi-gloss black spray lacquer sprayed onto a mix palette and hand applied using a cloth to achieve the same look as the original strips - we couldn’t get the paint formula and I also ended up doing the same for the side air intakes on a Ferrari Testarossa. We prepped cars to Concours standards for car shows as well as accident repairs and restoration. I worked doing pickups, deliveries, damage/repair/detailing assessment, hands on detailing, prepping and painting, brush-touch paint repairs, materials sourcing, event organising and sound setup and mixing for car shows and weekend meets. I also set up the infra-red tracked mobile lamp system for one of our spray booths which was completely computer controlled with laser range finders and inbuilt heat sensing for even heating of car body panels - the wavelength of infra-red was set to penetrate and heat the paint from inside the skin - designed for the water based paints used on modern vehicles.
The input transformers on the old Neve consoles have a green hammer finish casing as well. Seems like green was a popular color in the UK.