240z Acid dipping

kris broughton

Club Member
Hello everyone,

Has anyone had there shell dipped and zinc primered, so they know what there dealing with and how many holes there are to repair?
 

Turn & Burn

Club Member
I’ve not done a full shell but I’ve done panels that are generally sound. Roofs, doors, hatch etc. also done engine blocks and heads. The place I go to does electrostatic dry painting so you get a really tough paint finish. Too many horror stories about full shells for me, but they do loads of them so can’t be all bad. I think it’s all about the careful flushing afterwards which in a full shell is tricky.
For a bodyshells I prefer to bead blast, the local blast shop uses plastic granule which is a bit more expensive but doesn’t heat warp the panels if u overdo a tricky bit.
 

Mr Tenno

Digital Officer
Staff member
Site Administrator
There was an album of photos on Facebook recently that showed the results of an acid dip and primer from an apparently reputable company in Europe - rust left in hidden places, acid residue trapped in between metal skins:

FB_IMG_1583351759434.jpg

If you care about longevity, it's probably best avoided.
 

richiep

Club Member
It really depends on which process you go with - not all dippers are the same. I’d avoid the ones that strip with acid, especially if they use hydrochloric acid. That’s the worst offender for getting trapped and not properly neutralised.

I used Enviro-Strip in Tamworth. They use phosphoric acid in one of the dip stages, which is less problematic, but the actual paint stripping is done through pyrolysis - slow bake to 400 degrees in a large oven. That turns everything to ash. The dips wash the residue off, neutralise any rust, and zinc phosphate the shell. Guess I will find out how it works long-term; my only criticisms have been that here and there, in certain tight spots, the ash residue of things like seam sealer have not been completely removed, needing to be manually dealt with. Also, I’ve had a couple of spots where some dip fluid has shown itself. On the plus side, because it will be some time before the shell is finally painted, I’ve got lots of opportunity to track down any issues like that and deal with them. Also, I will be drenching all inner structures with Dinitrol ML cavity fluid and 3125 wax - that should prevent anything nasty surfacing. The ML in particular is very runny and can get into seams - which is absolutely what you want.

My opinion- use Enviro-Strip, or go for media blasting and manual stripping of some form.
 

kris broughton

Club Member
I have read good things about them, and I'm now booked in with them 6th May after a really good conversation with them about the process :) fingers crossed how much of my cars left at the end as I know it's not in the best shape I'm trying to save it
 

Garaculas

Club Member
Interested how you both get on with this long term. Something i’m looking at for mine eventually but as you i’ve heard loads of dipping horror stories that puts me off.

Good luck and look forward to updates!
 

kris broughton

Club Member
I will be documenting my whole progress and also getting pictures from the company during then when it's home I will see what i can find hidden etc and document that
 

Albrecht

Well-Known Forum User
I will be documenting my whole progress and also getting pictures from the company during then when it's home I will see what i can find hidden etc and document that

I think the "...see what I can find hidden..." part is a key point here. The *trouble* (not everyone agrees) with any kind of chemical dipping is that you literally cannot see what is hidden unless you drill out all the spotwelds and take all the sub-sections of the car apart. What looks sound from the outside can often reveal a sandwich filling of surface rust when split apart. If moisture has invaded (it probably started on the day the car left the factory...) it's obviously not a good thing, but it can lay in a relatively static state for years without getting worse. Flushing that out with strong chemicals - often only getting in there under capillary action - is all very well but it *can* start a whole new process of trapped chemicals, incomplete flushing and then sealing-in with etch primer.

Case in point: I've just started work on an engine crossmember which was - two or three years ago - Pyrolysed (oven stripped), then chemical dipped, etch primed and painted. I wasn't happy with the lower part (car had been jacked up off the centre plate and it was dented and ugly) so I drilled out all the spotwelds in order to fabricate a replacement. When I separated the two halves I was shocked to find some residue of the dipping chemicals and a new, active layer of rust. If left to develop, I reckon it would have become quite nasty. So I'm having the whole thing - minus the lower part - blasted, and I will weld on the new lower section after using weld-thru primer, then seal and paint.

I had a whole bodyshell soda blasted and etch primed after structural repairs (inner & outer sills, doglegs, floors and floor supports, air tubes and lower radiator crossmember), and I think I ended up with a very sound 'shell and - hopefully! - no nightmares about festering seams...

Soda-1.jpg
 

richiep

Club Member
I think there's pros and cons to all approaches in the end, and we all take a chance as we try to select an approach that best meets what we think is needed for the case at hand. In my case, I went for the pyrolysis and dipping for Dixie because there were certain areas that had become rusty due to the car's rodent infestation that would not have been reached with a "line of sight" approach like media blasting. Nests and toilet areas in difficult to reach locations!

Soda blasting has its own issues - specifically, a bit like dipping, neutralization. It needs to be fastidiously neutralized with salt removers otherwise paint adhesion problems can manifest. You do find the odd bodyshop that won't work with a soda-blasted shell precisely for that reason. But its all down to finding the right people and attention to detail.

Overall, I'm pretty happy with my shell. When doing stuff like the dogleg replacement, it was heartening to see how clean the inner structures were, nicely coated with the protective zinc wash. But I will be going over every seam as I progress around the car cleaning out any ash residue and watching for signs of dip moisture.

But, just like media blasting, nothing will properly get in and remove the rust that forms between spot welded panels. Short of breaking everything apart, you'll never get every dot of rust. Thus, its a best efforts process and use lots of cavity wax/fluid to mitigate/inactivate those areas.
 
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