Thorn EXP botched powdercoating

[hutzelbein]

A year ago I bought a NOS Thorn EXP frame directly from Thorn, which was advertised on this forum. Apparently they stopped making the EXP a while ago, and when this frame turned up in my size, I jumped at the opportunity. I already own a Sherpa and a Club Tour and have been very happy with these bikes.

Unfortunately, I had no time to build up the bike last year. When I received the frame, I only had a quick look. I noticed that it seemed to have a bit of a strange powdercoat, e.g. the steering tube of the fork was powdercoated. I had not seen anything like this, but didn't give it much thought. However, I now have some time to build up the frame, and I realized, that there's no way I'm going to be able to install a crown race! On closer inspection I saw that the frame seems to have been powdercoated without any protection of the threads and cantilever bosses. The powder is everywhere.

I'm pretty disappointed, because Thorn did not mention a botched powdercoat. This leaves me with the question: what can I do now? Can the frame be salvaged? Obviously I hope so, because I spent a lot of money on it. I know that it is a hand built frame, and therefore was a bargain - but it's definitely too much money for a frame that is unusable.

I don't really want to take off the powdercoating by hand with sandpaper. Not sure if this would be possible at all, but even if it would, I guess it would take me ages. I'm not sure if having it sandblasted is possible, since I assume that the tubes are high quality and therefore thin walled. There is also the issue of the powder in the threads. The frame is fillet brazed, which probably makes it more delicate than a welded frame?

Has anybody had a problem like this and found a solution?

Here are two pictures of the fork (the frame doesn't look better, either):

[il padrone]

I don't think you have an insoluble problem there. When I bought my Thorn Nomad a 'frame-prep' was an option at purchase. I didn't get it done then, but simply got my LBS to chase the threads with a tap, and also to fit the headset. You could do this yourself if you have all the thread tap sizes needed. The fork crown race seat could be filed with care. However for the small cost of $20-30 it is worthwhile getting a shop to do it. If they're any good they'll have it all done in an hour or two.

[Danneaux]

Hi Hutzelbein, and welcome to the Thorn Cycling Forum!

Your powdercoat dilemma can be resolved quickly and easily by use of paint stripper or gasket remover. Here is a bicycle-related post on the matter: http://forums.mtbr.com/bike-frame-discussion/myths-reality-stripping-powder-coating-frame-838598.html ...and a whole customized Google Search on the topic: http://tinyurl.com/ler78sj The chemicals cause the plastic to bubble and peel, and it is a fairly simple matter to then scrape off what you don't want, much as you would with paint after stripping. Carburetor cleaner has much the same effect. No metal will be removed, and you will avoid the tedious task of hand sanding. More details here: http://forums.thecustomsabershop.com/showthread.php?8667-How-to-remove-powder-coating

I have done this on old frames to salvage the tubing for special projects. Using the Permatex gasket remover, it goes pretty quickly. Just be patient and give the stripper time to work, reapplying if needed and do take care to apply it only where desired. Be careful in your application and masking so only the steerer, crown race seat, and brake boss pivot surfaces are exposed to the stripper.

As for the threads, a tap will clean those out nicely. A 5mm and 6mm tap with "T"-handle should cost little and see the threads cleanup nicely, as the threads are already cut -- just clogged with powdercoat, which is essentially melted plastic.

I hope this will work for you. The frame is a lovely color and when completed, should make a lovely bicycle. I'd love to see photos of it in the gallery.

Best,

Dan.

[hutzelbein]

Thanks for your help! Stripping parts of the powdercoat sounds promising. I'll have a look what my local hardware store has on offer.

What do you use for masking the powdercoating you want to keep?

I'm going to ask at my LBS if they can redo the bottom bracket and will have a look for obtaining 5mm and 6mm taps to do the other threads myself.

[Danneaux]

Hi Hutzelbein!

Before using any of these very strong solvents, a few cautions:
1) Use them outside, with plenty of ventilation. I set up a fan once when I did this outdoors on a day with still air.
2) I wore my 3M charcoal brazing mask. And eye protection. And two layers of nitrile gloves taped to the sleeves of my coveralls. The MSDS (Materials Safety Data Sheet) for the Permatex 80646 is here: http://www.permatex.com/documents/MSDS/18_GHS-English/80646_18.pdf It contains Dichloromethane. Not as bad as the 1-1-1 Trichloroethane I used to work with, but nasty stuff just the same. If you get *any* on your bare skin, stop everything and wash immediately.

Unless you wish to remove all the paint from a frame, I'd suggest doing a section at a time, positioning the frame to make sure any runoff doesn't get on the paint you wish to keep. Masking is problematic because the solvent can creep under the adhesive and make a mess. Best way is to avoid the need for it. When I have masked, I had the best luck using extra layers of paper masking tape, but it is best to avoid getting the remover on the tape if you can avoid it. The best way to do that is through spot-application.

I would suggest forming a cone out of a sheet of printer paper, taping the overlap and leaving the bottom open a centimeter or so to make a disposable funnel. Get a small, low glass jar you can dispose of...maybe a Marmite jar if it is glass. Put the cone in the jar, spray the remover at the inner part of the cone, and let a small amount of solvent collect in the jar. Work fast before the VOC's (Volatile Organic Compounds) evaporate. Use a natural brush (boar bristle or horsehair; plastic will dissolve in the solvent) to place the remover where you want/need it. Try to do a section at a time and hang the frame so no drops will fall onto the powdercoat you want to keep. For example, if you wish to clean up the steerer, make sure the dropouts are up. For brake bosses, make sure the opening is down so the solvent will run off if it drips at all. A wire coathanger through the mudguard braze-ons works great to hang the fork from a tree branch or cording so you can work freely without runback.

I've had good luck using a combination of steel spatulas/putty knives and thin 3M Scotchbrite pads to lift the dissolved powdercoat off the surface. Once it has bubbled free, it really is easy. Leave it too long, however, and it wants to sort of turn back into powdercoat and can be harder to remove. The ideal time is when it starts to form bubbles that lift off the surface.

If you run into any problems, give a shout. It takes a little time and patience for the chemicals to work, but almost no labor compared to mechanical removal methods.

Best,

Dan.