Stripping down a frame

[whisperdance]

Hello again, folks!

I want to ask you some questions.
What is the best way to strip a frame? Is it better to paint it, to varnish it or can I left it in bare aluminium?
By the way, what is powder coat? Does this technique leaves a rough layer of paint? If so, isn't the bike very easy to scratch?
I will have a frame to strip down to bare aluminium and I have not decided what to do with it. I have a new crosslink carbon fork and a carbon swingarm to put in the bike...

Any help would be appreciated.

Regards, Ricardo.

[Matno]

There are several liquid paint strippers available. Be sure to wear gloves! If you have access to a place that can do it, sandblasting is probably easier, quicker, cheaper, and much cleaner...

As for finishes, if you want the silver look, your best bet is to polish it nice and shiny, then clear coat it. You could also clear coat over a sandblasted frame for a nice "brushed metal" look. But clear coat is a must if you're doing a "bare" finish. Otherwise, bare aluminum will get dull VERY quickly. It oxidizes just like steel, but instead of turning rust color, it turns whitish. Not pretty.

Powdercoating is a good option if you want a very durable finish. If done right, it is very strong and looks a lot like regular paint. It is more durable than regular paint, and almost all bike frames are "painted" using powder coating these days. The process is something like this: they take a bare, sandblasted piece of metal, spray the 'dry powder' paint material on it just like liquid paint, and then put the part into a baking oven and heat bake it to I think around 1500 degrees. The paint in powder form melts and covers the surface. No runs, no sags, no orange peel, just the smoothest finished surface you will ever see. Because of the composition of the paint material and the way it is baked on, it is probably the most durable paint finish available. I think powdercoating is available in matte finishes too, but most I'm familiar with are highly glossy.

[Simon]

If left bare or polished you should
coat the frame with lacquer,
Aluminium does corrode (though not in the same way as steel).

Simon.  

[whisperdance]

Thank you guys.

I believe I prefer a paint stripper, as sandblasting is a little more aggressive for the frame.
Matno, you say 1500 degrees. Isn't that way above the heat treatment temperature of the aluminium. More than that, the aluminium would melt before reaching the 1500 șC...
When you say clear coat, is it like a varnish or something more like an anodization process?
Sorry but sometimes I get "lost in translation" with these technical terms" (native language: Portuguese...).

[will]

Paint stripper worked well for me. It's important to use the type that comes in a gel. If it doesn't have enough viscosity, it will drip off before it really goes to work.

Steel wool, rubber gloves, and eye protection are very necessary. This is a dangerous chemical mix.

I should probably coat my bare frame, but it still looks good after 6 months. I have rubbed it down with WD-40 a few times and that seems to help.

Since I don't care how it looks, this may not be great advice. Check my gallery and see what you think.

Also in my gallery is a powder coated white bike. I think this was a mistake. The paint has added roughly a kilo to the weight, it's a softer than enamel finish, and loses it's luster quickly. I gave up trying to keep it shiny and just clean it with steel wool! It's a mud magnet, but looks pretty when it's clean.

Powder coating is a process that uses an electrostatic charge to attach powdered paint to a metal surface. When the the piece is completely coated, it's exposed to high temperature infrared (about 400F) and the powder melts onto the metal. When cured, it has a smooth, high gloss finish. One major benefit is that it is much better at filling cracks and rounding off sharp edges than liquid paint.
The downside is that it's soft and tends to oxidize faster than enamel.

Be patient, it's a hard job.

[SLIM]

 the main reason manufacturers use powdercoat is that it has two functions
when aluminium is welded it need time to "settle/cure"
but if you heat it it cures in no time
so they powdercoat
the powder needs about 400 degrees to melt which is the same temp as ally is cured at ....bonus !!
two jobs in one

[whisperdance]

That's why some years ago we used to see in the bicycle specifications something like "Aluminium 7005 - T6", T6 being the specific heat treatment.
By the way, it's this kind of material and treatment of which pro-flexes were made.
I really like the new paint job on the bikes using matte colours. They go very well with the carbon stuff... although I believe that some sort of anodized treatmet with a titanium colour would fit perfectly...
One thing for sure: I will have to polish it veeeery well...

[bmwcarver]

Hey all, check out my gallery, my frame looks every bit as good now as when I first finished the strip/polish job.

Whatever you do, DO NOT SANDBLAST!  I did that once at my old job and it ruined the aluminum piece I was working with.  Too agressive, if you must blast use the BEAD blast.  The glass beads are finer and don't cause near the harm.

To get a nice polished finish all one has to do is use "Dad's Easy Spray Paint, Stain and Varnish Remover".  It came with a spray bottle to spray it on. Paint was gone within a total of 30 minutes with re-applying only to a few areas that were stubborn, then just rinse with a hose.  As for polishing, use a small vibrating sander such as the Mouse from Black and Decker.  Start with around a 1000 grit paper and work up to 2000 grit finishing paper that you can get from an auto paint supply.  Sand down the entire frame each time progressing to the finer grits.  Once you get to the 2000 grit it will be starting to look like dull chrome.  I learned this technique while working at Alcoa Aluminum where we polished sheet aluminum for use on aircraft.  To finish off and protect the finish use "Mother's aluminum wheel polish" to bring out the mirror shine!  Mother's has a protectant in it so you WON'T need to clearcoat.  FWIW, clearcoating a polished aluminum finish will scratch extremely easily as the clear paint won't adhere well to polished aluminum.  I then used a good automotive wax to further protect.  I warn you though, wear gloves and preferably a dust mask while sanding. It will turn everything it touches BLACK!  Don't need the dust mask while using the polish, but gloves still recommended if you don't want your fingers turned black.

I usually retreat with Mother's and the wax once a year at the beginning of the season but I didn't this last year, and the bike still looks great!  I will be doing that this year again, as it makes the bike much easier to clean, just need a damp wrag to wipe it down and a soft dry cloth to dry and buff back to luster!

[Matno]

I don't know about the temps. I was just going by what someone else had said. However, I definitely was not referring to 1500 C! (That's much hotter than "our" version of temperatures...) 400 degrees Fahrenheit sounds more reasonable.

I meant to say bead blast, not sand blast. Definitely! The bead blasting is what gives it the nice smooth, brushed finish. Sand blasting gives you a lighter frame! (Because it eats part of it away!)

Powdercoating is VERY dependent on the quality of the job. Like I said before, most bike frames are powdercoated at the factory these days, and it is more durable than most liquid paints. I've heard complaints that it is so durable that you don't notice cracks that form in the metal under it!

Mother's polish works well, but I wouldn't say it's as "maintenance free" as a quality clear coat. However, a cheap clear coat sucks. I have a bare aluminum frame like that (I specifically bought it because I live in the Bronx and needed an "ugly" bike that won't get stolen!) and it looks terrible. The clear coat looks almost like I rode the bike through a lot of salt, except that it doesn't wash off! Cannondale makes beautiful examples of a clear coated, brushed aluminum frame. (See last year's Prophet, for example).

Like you, I kind of like the look of a matte frame. I used to have a beautifully anodized purple frame. Anodizing is probably even more durable than paint (as far as never peeling or chipping off), except that it scratches easily, and when it scratches, it's very hard to cover the blemishes. You can't just add a dab of matching paint...