Dipping/Baking/eCoating/Powder Coating tub questions

[Tom '74 911]

Hi -
I like the thought of stripping my car to a bare shell and starting from scratch w/a clean slate - a big project for sure, but something to dream about now and then. I've read a bunch of past threads and still am trying to wrap my head around some of these processes and have some questions.

Dipping -
I'm assuming one would have to strip EVERYTHING, even down to the VIN plates so they wouldn't get "eaten" correct? Would it be prudent to drill a bunch of holes in strategic places so that the acid can get to everything and more importantly get washed out of everywhere? Is this process one that can be used successfully w/Porsches (unibody) vs typical streetrod? Every time this comes up, it seems someone points out the dangers of not fully rinsing all the acid out. Can anyone recommend a facility that could dip a 911 somewhere in the Pacific NW? I've searched the net and have come up empty - have all these places been shut down?

Baking -
This is an intriguing option to me. I've followed along on the forum and seen photos of a few projects done by eimkeith @ zuffenhaus racing & fabrication that have included baking in a large oven to turn everything (paint, sound stuff on the floor etc...) to ash. Anything left is taken care of w/a light media blasting. Can someone point me in the direction of a place that might do this somewhere in the Pacific NW?

Something I am unclear of w/either of the above options is - how the heck do you coat the hard to reach places once the ENTIRE tub is down to bare metal? I'm thinking places like: inside the tunnel, inside the rear torsion bar tube, inside the rockers (assuming they're not cut open) where the heater tubes run, way up deep in the rear fender recesses - all the nooks and crannies and hidden voids that would no longer have ANY protective coating on them. How do you blast a bunch of powdercoating into the rear torsion bar tube and NOT fill the splines where the torsion bars go? Or all the pre-threaded nuts - like the accelerator pedal bolts, or the torsion bar covers etc... Do you plug those up or have to chase every one after they get filled w/paint?

Assuming one's starting w/a bare metal tub, doors, fenders etc... What is the most durable finish to coat the bare metal with? Powder coat, eCoat. . . ? I'm assuming eCoat is a process similar to acid dipping, except instead of getting dipped in acid, the parts get dipped in a big tank of paint, then oven cured - is this correct?

I know a lot of this has been discussed before, but I'd really like to learn more of the real details about what something like this really involves.

Thanks,
Tom

[DUK]

It's a long but well worthy project.

Acid dipping- I called three different places in our area (call some body shops or restoration shops in your area, they'll know who to send you to) and recieved the same exact answer from all three. They would do it if it was a racecar. Streetcars and showcars were out of the question with them. The reason being, leaching of the products later ruining the paint and body work.

Baking- I did not do this procees to strip the t-coating (wish I had). I have seen several of the cars Kieth and Aaron at eurowerks have done and will do my next one that way. I spent the better part of a month stripping the coating off with a propane torch, never again.

As far as getting everything coated again, I used a good Dupont powder and we turned the charge up on the gun to help with adhesion and being able to blow the powder up in the nooks and crannies. The tunnel, rocker area, and torsion tube areas all were fairly easy and we made sure we had good coverage with a mirror and flashlight. The hardest part was above the rear wheels (wheel well area), but with a little persuasion and preheating we were happy with the coverage. The tub has been coated now for almost a year and no signs of problems.

Here's some encouragement.

[Buckterrier]

Short answer... Using the best paint in the world will not stop corrosion without proper prep. An iron or better yet, a zinc phosphate on the bare steel then an EPOXY primer. Whether it's powder, liquid or the best option, e-coat. You probably will have a hard time finding a tank large enough to have the tub e-coated but that would be best. If you'd like I can investigate tanks in your area. As far as phosphating you may find a job shop that has a wand type cleaner utilizing a cleaner/iron phosphate.
Good luck.

ps. not sure how turning up voltage helps adhesion?, will help to build film though.

[gestalt1]

i've tought a lot about these problems as well. i had my car media blasted thinking if the blaster can't get into those closed off areas then the original paint/coating would remain. the problem is if there is rust or moisture getting trapped in those areas they will always bee there, the tub will not be factory clean sheetmetal after media blasing. the bake-off oven idea seems to be the best and i've seen a few race cars with extra holes in inside rocker areas so paint can be sprayed in. i think it would make sense to cut off rusty rockers etc before stripping so those areas can be accessed. i remember a 57 chevy that was chemically stripped and after the rear quarter was removed the inside area looked awful, all kinds of acid damage to areas that could not be cleaned out.

[1972_911T]

I had my car heated in an oven then acid dipped zinc phosphated and e-coated, acid dipping alone will not remove the underseal it need oven removal first. Theres a place here in the UK that carries this out, no good to you guys in the US but a good source of info on the process.

http://www.surfaceprocessing.co.uk/

Pics of my car that has been e-coated can be found here


http://www.ddk-online.com/phpBB2/viewtopic.php?t=16695&postdays=0&postorder=asc&start=0


Steve

[eimkeith]

Good comments here - I think the ultimate process would be the bake and wash (oven, then blastic with zinc/phosphate to clean the chassis) - then perform all rust repair/welding work, followed by a quick dip in the acid tank (with the aforementioned holes created in the enclosed rockers and whatnot so the liquid material will come out quickly and the rinse step is more effective) prior to an e-coat bath. This would get you a corrosion-free, protected shell, at least as protected as possible.

Unfortunately, I know of no single source locations for this work - our bake-off and powdercoater is a seperate sub than our acid-dipper, and our e-coater (try finding a tank large enought to do the 911 unibody in North America that will talk to you) is a completely different business also.

Add in the time. QC checks and travel between the shops and you end up with a significant expense. However, the job is thorough, and with a trip back to thew powder coater to put a base coat on the interior and underside prior to paint, you have an essentially new unibody, and a better end product than the old bodyshop color-change process.

What's a new 911 chassis worth in the end? How much value is there in better-than original corrosion protection on these cars?

Incidentally, we started baking cars because the acid-process didn't seem really well suited for cars with ROLL CAGES - the leaching out is apparently exacerbated with the tubing - not enough holes in that stuff for a good rinse typically.

[chris_seven]

We have spent a lot of time looking at the various methods of bare metall treating bodyshells and have tried several techniques with varying degrees of success and I thinbk it is good to summarise the various advantages/disadvatages as we see them:

Acid dipping - The company in England that do most of this work is Surface Processing as already stated. There website says that they use an 'Advanced Dehydration Technique' to remove underseal, mastics etc - this is followed by acid dipping and washing.

As far as we can determine the Dehydration technique is to put the shell into a Burn Off Oven and heat to around 450 degC. As far as we can ascertain the burn off oven does not use an oxygen free atmosphere and the paint etc. burns and can result in surface temperatures of 1000degC.

There are many threads posted on the DDK website in the UK pointing out serious levels of body distortion using this process and we have certainly seen 911 bodies that have suffered quite badly following this treatment.

The acid dipping also concerns me and we have e-coated a few bodies using a local contractor that has an industry standard plant and e-coats Taxi bodyshell and also used to process the MGF bodies for Mayflower. They also e-coat bodies for BL Heritage (MGB, Sprite and Mini)

A few weeks after e-coating it is quite common to see serious rust coloured stains in th region of the seams. We recently seam welded a 911 race car for one of our customers and in some areas we had to abandon using a TIG welder as the contamination in the seams disturbed the gas sheild quite badly. We managed to MIG weld these areas more successfully.

The other problerm with dipping is that most contractors lower the shell into the tank using cranes. If the shell is not well supported it is vewry heavy when full of acid and can distort of lifted too quickly. This has not been a big problm with 911s but we had a Renault R8 which is rear engined and has a floor in the front luggage compartment and this bent quite badly and needed jig work to correct.

In general we are not greatly enthusiatic.

We have recently treated a shell in an alkali hot tank and this successfully removed all traces of paint and sealants including underseal but does not remove rust. We have used this technique on a couple of 'newish' shells and it has been quite successful.

We have also tried blasting with Alumina and this gives good results but as already pointed out it won't generally remove underseal and this has to be manually removed prior to blasting which is messy and time consuming. It is also a nightmare to remove all the media after blasting and even fitting the shell into a roller and using an industrial vacuum cleaner is never 100% successful.

We have just had a shell treated in a Controlled Pyrolysis Oven. This again is a heating technique but uses an Oxygen free atmosphere so the paint doesn't burn. When the shell is removed it is covered in a light ash which is fairly easy to remove. We removed the ash by Soda blasting and then washed the shell with a jet wash. We made a dosing unit and fed a very dilute phosphoric acid solution into the jet wash stream.

We fitted the car on a jig before and after the process and didn't find any distortion.

The shell has been treated for about 3 weeks now and hasn't discloured yet. Once we have strengthened and welded we will e-coat.

The problem with this technique is that it doesn't get into the box sections but as most of the old 911s we work on will have suspension pan and sill replacement it isn't may be too much of an issue.

[Hoghead]

Talk to Redi-Strip in Vancouver Canada.
The border is not such a big hassle and I have used them several times over the years.
Phosphate coating is the last step as I recall.

Be prepared for a bit of a shock when it comes back cancer free but a bit holey

[Tom '74 911]

Thanks for all the replies and discussion - especially those that have had first hand experience. I'm starting to get a handle on the options pros and cons.

Thanks,
Tom