lukasz

So the idiots I took my S&S coupled frame to decided to powdercoat the couplers even though I specifically told them not to. I am now about to begin sanding the powdercoat off. What process would be recommended for this? I believe that the couplers are stainless steel. I know some will say: why don't they fix it? Well, it is a long story but suffice it to say that I'd rather just take care of it myself.

So far I have started with 80 grit paper, and am thinking I will use that until I have mostly metal exposed, then I will step down to 220 and follow it with 400 or something like that if it looks like it is needed. After that, I have some rubbing compound and other mystical wet sanding liquids from my automotive days laying around that I figure I could finish the couplers and lugs off with.

My main concern is that starting with 80 grit could somehow damage the coupler or be too rough on the finish. Opinions?

mudboy

Ouch. Are there any solvents that would be effective on powdercoat?

If I had to mechanically remove powdercoat from something like a coupling, I would probably go for media blasting with a relatively light-impact media like walnut shells.

lukasz

Well, at least they didn't powdercoat the actual coupler teeth or thread. It is just the parts visible from the outside when it is coupled, so the paint is purely an aesthetic consideration. I did half of the job yesterday. I am just having trouble reaching a section of the coupler lug right next to where the thread begins. I may get a wire wheel or sanding wheel for it as these stainless steel pieces don't seem to be very sensitive.

Scooper

Jasco Paint & Epoxy Remover is very effective for removing powder coating and paint. Most Ace Hardware stores carry it.

It's pretty nasty stuff, so if you decide to use it make sure you read the MSDS.

You can mask off the tubing at the S and S couplers to prevent damaging the powdercoating on the tubing itself.

lukasz

Geez, that stuff sounds killer based on the MSDS. Sanding takes a long time but I think that at this point I will just stick to that--for the sake of having all the parts end up with the same finish as well.

Falanx

It's hardly... the same mix is sold in the UK under the Nitromors brand name. As long as you don't get it in an eye, drink it, or leave it on your skin for any length of time, it'll be fine. As far as chemical methods for removing powdercoating go, I'd have gone with them over the sanding approach- not because you'll damage the couplers, but because the elbow grease involved in getting a nice polish back on the steel after you mince its surface with 80 and 120 grits will be monumental...

For reference, the blend you see on the MSDS is picked because although dichloromethane pretty much om-nom-noms any paint system you can think of, polyesters and polyurethanes tend to require a little activation - hence the presence of the methanol in there (the white spirit/Stoddard Solvent is just to stop the paint goo from sticking to the substrate again, and theygot it's CAS number wrong, whoops).

There's a lesson to be learnt here. If you don't absolutely trust them with your life, don't trust them with your paintjob and mask the important bits yourself :-)

pyeyo

I just took on a tube replacement on a powdercoated road frame and had terrible luck with aircraft stripper, it just turned the topcoat rubbery. I wound up peeling the layers using a razor knife like a draw knife then taking a wire wheel to it. this was one tough thick coating.
You might try scoring around it with an xacto knife then trying to lift it off by slipping the blade under the powdercoat trying to take as much of a chip as possible.
Just as a warning do not try burning it off, the fumes are deadly, I heard of this being down with motorcycle frame and the guy was hospitalized.
S & S BTCs are stainless steel unless you have a Ti bike then they are titanium.

unterhausen

interesting info about the fumes, I have never had to strip a powder frame, but I always burn the paint off for installing braze-ons.

Falanx

I'm gonna reach for my cell and call 0800-bull**** on the story you heard. Most powdercoats are polyester and their combustion products are no different really from a nice wood-burning stove. I hear similar stories often in my line of work and almost exclusively they're the third-hand report of someone who was basically offered an ambulance because someone else came in to find them trying to torch paint, and knowing a little but not a lot about polymer paint chemistry blew a gasket unneccessarily. Although I'd happily agree that much rather they did, than failed to act when they really should have...

The toxic effects you're alluding to are almost certainly due to the incomplete combustion of a polyurethane - well known in hypoxic situations or low flame temperatures to release cyanides and cyanogen fumes. I had a polymer chemist (she should have known better, really) try the same at my place when we ended up oxy-propaning a BSX34 polyurethane off a chassis. She knew polymers, just not thermal chemistry of fuel-air mixes. At over wo thousand degrees, the cyanides themselves just come apart and off floats the nitrogen wild and free, the carbon burning nicely.

While I acknowledge that there are some polyurethane powdercoats, the whole concept is a bit redundant because the very durability that we seek to acheive from polyurethanes is engendered best from two-part wet appplied polys.

Anyways, the TL;DR is: Elbow grease, damnit ;-)

pyeyo

So essentially you need to be able to identify the coating as polyurethane powder coating and use high enough heat to not produce cyanide off-gassing,\, thanks for the info. I'm now curious if this is why the frame I just tackled was so resistant to chemical removal and just turned rubbery with the application, it was amazingly thick for any coating application.

Falanx

Almost certainly.

But, when it comes to polyurethane, if that's what it does turn out to be, then chemical methods, even thermal, aren't really much use - in the end, whenever we've burnt a polyurethane to get it brittle, it *still* needed fine glass bead blasting to strip.