CrimsonEclipse

I have an older aluminum frame that is due for new paint.

Quick thread search showed several chemical paint stripper options but apparently, the really good chemicals were really REALLY toxic, bad for the environment and apparently, no longer available.

Is there a descent option that doesn't degrade the aluminum that actually works (post 2018)

Then there is sand blasting, which I might have access to a machine.
Is there any risk of work hardening the aluminum with a media blasting
(I always used it on steel but not aluminum)

Finally the mechanical option. Sand paper and wire wheels.
Seems to be the least accurate option and more susceptible to error.

Presently, I'm thinking of pricing a powder coating service but I'm also open to ideas.

terrymorse 

I don’t think sand blasting is hard enough to dent aluminum. The common way to alter the metal surface is by shot peening, which hits the surface with more force. Shot peening actually ******* [<-- banned word that means "lessens"] the growth rate of surface cracks, which is a good thing.

tFUnK

I think my preference would be media blasting, where media is dependent on the frame material. I'm no metallurgist but from YouTube videos on sandblasting it looks more gentle than I would have expected.

Maelochs

Citra-solv ..... wear gloves.

beng1

You can go to a hardware store and buy a can of paint stripper, and I would use fine brass wire brushes to remove the stripper and old paint.

I used to work in a metal fab-shop and did sand and shot-blasting, and you don't want to do that to an alloy frame. Aluminum is very prone to work-hardening and cracking and you want to avoid anything that would leave scratches, which would include sand or shot blasting and even sanding the frame by hand with sandpaper. The Smithsonian Institute's air museum used walnut hulls in a blaster to remove old paint and oxide from vintage aircraft aluminum parts. So if you can find someone to blast the frame using a medium softer than aluminum that is the key.

When I used to do sand and shot blasting 40 years ago, I could destroy a metal object with the process, I could curl thin metal parts up like leaves because blasting one surface and not the other would make it expand unevenly and warp it.

When you are done stripping, you may be able to find a shop that would shot-peen the frame, which works on steel or aluminum, it covers the surface with many small smooth craters which toughens the surface and removes all "stress risers" where a crack may start. It is what is done to valve springs and both steel and alloy connecting rods in internal combustion engines.

skidder

Ask at a few 'sandblasting' shops. I put 'sandblasting' in quotes as its not always sand - the media can be sand, dry ice, walnut shells, sodium bicarbonate . . . the list is endless these days. There are not many shops in my area that do only blasting, most are shops that do paintingt or powdercoating and blasting is just part of the process. The cost of getting a frame powdercoated includes the blasting. FWIW: I had a frame powdercoated about 10 years ago and it still looks great. It was cheaper by about 50% than a new paint job.

unterhausen

Powder coaters usually are able to strip paint. I would do that. It might be expensive, but it's worth it

mstateglfr 

The powdercoater I have used for 3 frames does the prep work, which means they fully strip the old paint with a media blast. Its part of the cost.

I have chemical stripped and then sanded probably 6 frames. Its a slow process, but it is very easy to complete properly. The citrus strip is weak, but if you use it in a warm area and apply it a few times, it gets most of the job done. Just spray on, wait, then take some towels and scrape off whats loose. Repeat a few times. Then use some sanding strips. Tear off an 8" piece, hold the ends in each hand, and run it back and forth along the tubes where there is still paint.

tomato coupe

I use SRAM disc brake fluid.

CrimsonEclipse

Thank you everyone for a LOT of great advice.

Brass is softer than aluminum?

I've seen someone (in another thread) suggest a rubber attachment for a drill but i wasn't able to find any additional information.

LV2TNDM

Sand blasting is considered too harsh for aluminum. Most bicycle makers won't use sandblasting, regardless of material. That said, removing powder coat is a two-stage process. First, the frame is chemically stripped. Second, it is media blasted to clean up the surface in preparation for refinishing. Even if you chemically strip paint from a frame, you'll want to media blast it just prior to refinishing. You need a nice, uniform, rust, oil & grease-free surface. Whenever steel is blasted, it's never touched by bare hands thereafter and painted/coated right away. Otherwise, micro rust spots will form, especially in high-humidity climates.

Maelochs

Brass is indeed softer than aluminum. And having stripped (with Citra-solv, a scraper, and sandpaper) and clear-coated a steel frame, I can attest that in a high-humidity environment you Will get rust. Aluminum, you can just clean it right before painting.

mstateglfr 

The OP isnt trying to strip powdercoat, the OP wants to remove paint and said they are thinking of then powdercoating.
As for steel being painted immediately after being media blasted, that can often happen, but I have seen large operations and a small builder definitely blast then shelve steel frames. It gets wiped down, any filler is applied, that is then sanded down smooth, it would be wiped down again, then chemical etcher can be applied. Priming then takes place after that.

Tusk

Laser Ablation. Removes everything from the base metal if desired and can be tuned to the wavelength of the topcoat to leave the primer if the right system is used.

seypat

Are any of these methods done electronically? I've read somewhere that electronic is way better than mechanical. Does the chemical method use an electric sprayer?

terrymorse 

Reported hardness for brass is slightly higher than aluminum alloy.

Reported Rockwell hardness:

• 6061-T6 aluminum 40-60
• Brass 46-90

GamblerGORD53

Let's see what it looks like. Alu doesn't rust. Is it really worth it??
I think it is best to sand off the top layer and leave the original primer.

Calsun

Plenty of effective paint strippers for a DIY paint removal. The days of commercial dip tanks ended in most states but no issues for small scale operators, including people stripping furniture for refinishing. I would only use a chemical stripper but be smart about it and do it outdoors with plenty of ventilation and even wearing a half mask with organic vapor filters attached.

CrimsonEclipse

I can't believe I still have to explain this:

Rust is an older terminology meaning RED or Turning Red. (old Germanic)

Rust is oxidation.

Aluminum certainly DOES oxidize meaning it WILL corrode.

I'm not sure if you guys do this on purpose to troll or you simply haven't read the 150,957 threads stating this.

BTinNYC 

If you're going to a powder coater, have them do it. At home, citri-solve is good and wrap the goo-ed up frame in saran wrap, leave it at room temp for a couple hours, then remove the paint & goo. Usually takes a couple sessions.

zandoval 

Do a detailed sanding with light weight sand paper. What ever does not come off stays. Then do a spray prime and sand again. Then do a nice thick coat of Gloss Enamel with a brush if you dare...

Bald Paul

Amazon.com : 3m gasket removal disc

Be aware that these discs come in different colors, which designate how abrasive they are. Check to see beforehand which ones are good for aluminum. Using one too 'hard' can take off aluminum material as well as the paint.

Iride01 

You'll be surprised how little time it takes to get to the bare frame with just some decent sandpaper or emery cloth. I did it once on a steel frame and in just about less time than one or two beers drank slowly. Of course I have a good selection of sandpaper/emery cloth to let me find the best for each area, nook and cranny.

And for places where the paint is good, just lightly sand it and feather it out to the places where you had to go to the bare metal. Though if you are powder coating, you should ask the person doing the powder coating. I don't know how normal paint behaves in the oven the bake powder coated stuff in.

CrimsonEclipse

I'm learning a LOT here.
1. I would have never thought to call them "bristle disks"
2. "yellow 80# abrasive bristle disc and green 50# abrasive bristle disc can be applied on hard metal, such as steel; White 120# abrasive bristle disc is designed for soft metal such as aluminum"

To everyone:

I failed to communicate an additional reason for the paint stripping:
There are a few areas where the paint has chipped showing the white powdery oxidation.
My intent is to strip the paint AND inspect for cracks

Iride01 

If those areas are few, you likely don't have a problem. Just lightly sand the existing paint. Where there is a chip or area of powdery oxidation, then sand that to the bare metal and feather the edge of the remaining paint around it so it's smooth. Unless you know about paints and painting, your biggest issue with going to the bare frame will be getting the correct primer and paint to make it last and stick for a long time.

A crack will very likely crack the paint too. So you'd already see the evidence of one.