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Reidy41
29th Jun 2020, 09:25 PM
Hello all

I am about to give some old panels of my Chev truck project a Citric acid bath to remove some of the rust. Once they come out of the bath they will require repair that make take a few weeks depending on available time. I will be doing one panel at a time. The truck probably wont be ready for paint for a year or so.

Therefore what should I put on the metal to protect it whilst I do the metal repairs and put it in storage for painting.

Thanks

Steve

BobL
29th Jun 2020, 10:11 PM
What sort of repair?
If its not welding I'd spray a Zn rich primer/undercoat on it right away.
If its welding I'd just wipe some light oil on it, and put the Zn rich primer/undercoat on it after its been repaired while waiting to repaint
If it comes back from repair in a rusty state - back into citric acid.

Mk1_Oz
29th Jun 2020, 10:12 PM
When I had my car body sand blasted I immediately painted all the dad's metal with etch primer. As I did the rust repair sections I painted more etch primer. Etch primer will not protect against moisture so keep it dry and avoid condensation.

You will need to neutralise the acid and flush with plenty of water.

droog
29th Jun 2020, 10:42 PM
Use a modern protection, epoxy primer.
Older primers were hydroscopic and would rust under the paint. Epoxy primer will seal the surface and protect from moisture.

morrisman
30th Jun 2020, 12:17 AM
I really like the Wattyl Super etch prime, it comes in grey and black , its a epoxy paint with a tough finish.

With the citric bath, the warmer or hotter the solution is, the faster it will work, its a rather slow method in a cold environment . Its a Summertime job for us Victorians !

Redminch
30th Jun 2020, 08:33 AM
Two things I have found to be good.

Gibbs oil is a especially made product that stops rust on any metal. Panels tools etc. It works well and can be painted over without any problems. So suits body panels, gives protection for months.
The other is basically phosphoric acid. This brand you can get at Bunnings. It is much cheaper than Gibbs.
Not the best phots but you can find Gibbs with Google.
When you take the panels out of the citric bath they will "flash" rust almost immediately. It helps stop the rusif you get a heat gun on them to dry them quickly.If you wipe them over with either product straight away they can be left for months without further treatment.387395387396

BobL
30th Jun 2020, 09:18 AM
When you take the panels out of the citric bath they will "flash" rust almost immediately.

That's only if you wash them, its the water that does it. Unless you are going to prime or paint immediately I don't recommend washing them.
Just blow dry with compressor and used a heat gun to get the acid out of the cracks.
Citric acid is a chelating agent and does not dissolve steel I've done lots of testing on this

Below shows a test run with the initially heavily rusted steel steel being dunked in various 10% acids (HCl - Hydrochloric, AC = Vinegar, Ax = Oxalic ND CI = citric) and then pulled out, blown dry and suspended in air for 6 days. NO WASHING

387397

Here again after 10 weeks. Oxalic acid wins hands down but the vinegar and citric have also not rusted much.
These pieces were left hanging up under a back veranda.
387398

For general use there's no need to remove any residual like the yellow green ferrous oxalic acid layer - just paint direct over the top.

hpa1
30th Jun 2020, 08:18 PM
Thanks for your input to this thread Bob L. Im just about to start rubbing back and repairing the panels on a '68 cooper S so this information will come in handy to preserve the finished panel prior to paint.

morrisman
30th Jun 2020, 11:03 PM
I do this sort of thing in Summer. After removing the part, I do wash it down with water but during Summer that isn't a problem. Before painting with the etch prime, I go over the part with a brass cup type wire wheel mounted on a 5" angle grinder, doing this removes any left over crud and it really polishes up the surface to a nice clean bright finish. Finally use a rag and a solvent, I use thinners , and rub over the surface to remove any residue from the previous steps, lots of gunk will come off with the rag wash. Use good gloves and be careful . If i am storing the part , I wrap it in Glad Wrap , it keeps the air away . A 50 metre roll is cheap

Wattsy016
7th Nov 2020, 07:06 PM
Further to BobL's post,
I occasionally use citris, however over the past few years I've used molasses and kephos as I find the item is always ready for the next phase and there's no retreating.
If there is heavy rust on a part(s) and I'm not in a hurry, I have a 10% molasses bath of 15lts and I put the item(s) in the bath for a week or more. Every few days I clean the foam off the top and when the foam stops, I know all of the rust has been eaten. There is a minor down side to this process in that it eats off any natural protection to the steel.
I then rinse the item, quickly dry it, then give it a thin coat of phosphoric acid which is then wiped off with a damp rag.
Once i have a few pieces, I give them a coat of kephos and store away until it needs to be painted, repaired or welded onto a car being restored.
Cheers, Mick

PS. This is my first post.
I play around with cars and currently doing a major restoration of a 1964 Alfa Giulia Spider.



Citric acid is a chelating agent and does not dissolve steel I've done lots of testing on this

Below shows a test run with the initially heavily rusted steel steel being dunked in various 10% acids (HCl - Hydrochloric, AC = Vinegar, Ax = Oxalic ND CI = citric) and then pulled out, blown dry and suspended in air for 6 days. NO WASHING

tiprat
7th Nov 2020, 08:11 PM
What about a coat of lanolin?

BobL
7th Nov 2020, 08:20 PM
Further to BobL's post,
I occasionally use citris, however over the past few years I've used molasses and kephos as I find the item is always ready for the next phase and there's no retreating.
If there is heavy rust on a part(s) and I'm not in a hurry, I have a 10% molasses bath of 15lts and I put the item(s) in the bath for a week or more. Every few days I clean the foam off the top and when the foam stops, I know all of the rust has been eaten. There is a minor down side to this process in that it eats off any natural protection to the steel.
I then rinse the item, quickly dry it, then give it a thin coat of phosphoric acid which is then wiped off with a damp rag.
Once i have a few pieces, I give them a coat of kephos and store away until it needs to be painted, repaired or welded onto a car being restored.
Cheers, Mick

PS. This is my first post.
I play around with cars and currently doing a major restoration of a 1964 Alfa Giulia Spider.

The thing most people do incorrectly after using acetic/citric/oxalic baths is to wash parts with water - the trick is NOT to wash them with any water but just blow dry with a compressor and provided its left out of the weather it should stay rust free for some time thereafter without any treatment. Oxalic will stay rust free for many months, even years, so no mucking around with washing sticky molasses or extra coatings of PA etc.

clear out
9th Nov 2020, 10:19 AM
Love the smell of kephos :no:
At North Sydney TAFE the head teacher at our resto class wouldn’t let students apply it in the workshop, you’d be banished to outside.
Works on Tools if your workshop has the rust problems mine does and you don’t want your tools greasy.
H.

Wattsy016
9th Nov 2020, 10:48 AM
BobL, I agree that the part should not be washed with water except for the molasses. It needs to be washed off as it's impossible to paint over.

Clear Out. Shame they closed that section of tafe.
We all have fond memories.

BobL
9th Nov 2020, 11:47 AM
BobL, I agree that the part should not be washed with water except for the molasses. It needs to be washed off as it's impossible to paint over..

Yep agree that sticky stuff has to be removed before painting. I was put off a bit from molasses by the smell and had nowhere else to put the container except inside my shed. I tried putting the tank on the back veranda but SWMBO put paid to that in short order.

For smallish objects I now use citric/acetic/oxalic in my electrolysis tanks made up out of 150mm and 100 mm diameter PVC pipe. I have several ranging from about 4L to about 8L. They have PVC end caps glued onto the base and a threaded coupler with a an O-ring screw cap on the top. For bigger stuff I use a 50L black HDPE tub.

jhovel
16th Nov 2020, 10:47 PM
I've recently started using Super Cheap's "Rust converter Primer" (not their "rust converter" in a similar bottle!). It is effectively phosphoric acid, a chelating agent and a primer in one. It is milky colour and turns black where there is rust (presumably ferric phosphate) and slightly shiny when dry. Paint sticks to it like the proverbial to a blanket. It can be sanded and flap wheeled for welding easily. I tried it first after wet blasting some stuff which instantly rusts of course. That was several years ago, and both the subsequent paint coat and the steel are in perfect condition (outside structure). I've used it since for protecting all kinds of steel stuff for storage and eventual painting. It seems to prevent rust for several month stored outside....

droog
16th Nov 2020, 11:09 PM
I've recently started using Super Cheap's "Rust converter Primer" (not their "rust converter" in a similar bottle!). It is effectively phosphoric acid, a chelating agent and a primer in one. It is milky colour and turns black where there is rust (presumably ferric phosphate) and slightly shiny when dry. Paint sticks to it like the proverbial to a blanket. It can be sanded and flap wheeled for welding easily. I tried it first after wet blasting some stuff which instantly rusts of course. That was several years ago, and both the subsequent paint coat and the steel are in perfect condition (outside structure). I've used it since for protecting all kinds of steel stuff for storage and eventual painting. It seems to prevent rust for several month stored outside....


I believe it is the same as the Rustoleum Motorspray rust converter, tannic acid combined with a primer. Great for where there is a light coating of rust in areas that just cannot be reached.