Rust Removal using Phosphoric Acid

[mgcjag]

Hi All.....from what im hearing and reading about Phosphoric it dosent need neutralising....its not a rust remover but a convertor....and will continue to convert rust and not attack sound steel.......what do you think of spraying it into box sections.....im currently working on an old chassis with someone....its basically sound but with some small areas rusted through.....these bad bits are being cut out and new pieces welded in.......however when you look into the long sections you can see rust.....not rotten and not just surface.....my thoughts are to soak it with phospsoric......but it will have to stay in there.......then spray with wax oil ect......or as mentioned above are you left with salts on the clean steel parts thtr wernt rusty .....whats your thoughts....thanks Steve

[JagWaugh]

Hi All.....from what im hearing and reading about Phosphoric it dosent need neutralising....its not a rust remover but a convertor....and will continue to convert rust and not attack sound steel.......what do you think of spraying it into box sections.....im currently working on an old chassis with someone....its basically sound but with some small areas rusted through.....these bad bits are being cut out and new pieces welded in.......however when you look into the long sections you can see rust.....not rotten and not just surface.....my thoughts are to soak it with phospsoric......but it will have to stay in there.......then spray with wax oil ect......or as mentioned above are you left with salts on the clean steel parts thtr wernt rusty .....whats your thoughts....thanks Steve

Steve,

The phosphoric passivates the surface (I think that is the right term), and removes rust.

The passivation converts the top surface to black iron oxide, only a few molecules thick.

Once you rinse the acid off and blow/wipe the water off you have a protective layer of Iron oxide. On the small parts I initially tried phosphoric on I just let the acid drip off and airdry - the areas where the drip in the corners evaporated had a sort of crust left over which stopped paint from adhering.

My approach would be to spray phosphoric in until the rust is gone and the conversion layer is created, then I would drill drain holes and spray with water, then blow dry, then once the outside is painted,apply rustproofing to the inside.

I wouldn't be happy with leaving acid in place, neither liquid, nor evaporated.

[rfs1957]

I second this reticence about painting over evaporated phosphoric as it can definitely leave a friable deposit which is not absorbed or integrated into any paint that follows ; if it can do that on accretions that are abvious to the eye, it can only be doing the same thing on an macroscopic level.

Hence the insistence of people like Rustbuster to encourage users to clean it off ?

HOWEVER, the same manufacturer retails Fe123 (which, incidentally, it says CAN be sprayed into box-sections etc and then just drowned in the usual Waxoyl/Dinitrol etc) of which it says that both "one-pack and two-pack paints are unaffected by the residual salts".

Can I boil Jaguar doors ? I'll settle for rinsing out with the Rustbuster Chlor-X salt-remover, followed by fresh-water, then hanging on a radiator.

As none of the alchemy I'm reading here or elsewhere, and particularly not my own, is particularly convincing, I shall ensure my fingers are crossed throughout the whole operation.

[JagWaugh]

Can I boil Jaguar doors ? I'll settle for rinsing out with the Rustbuster Chlor-X salt-remover, followed by fresh-water, then hanging on a radiator.

Boiling is gonna be difficult.

I boil the small parts in TSP to make sure that any oil, wax or contact cement is gone before I start further finishing processes - if you have glue, oil or wax on the surface then the acid won't get to the steel, and who knows how that barrier will hold up over time?

For a box section I would say it is probably free of oil and wax. I would spray the acid with a garden sprayer and let it work (possibly repeating), then spray rinse with hot water, then spray rinse with alcohol, then arrange a hair dryer or such to get it dry.

Not sure about Chlor-X. If you're working with Phosphoric, and you hot water rinse while the last application of phosphoric is still liquid, then there won't be any crystals left over.

[Hugo]

Jenolite, which I beieve is phosphoric acid, specifically states NOT to rinse with water. It advised to apply the stuff, work it in with a brush, leave till it turns grey, apply another coat & repeat, leave for a bit, then apply another coact and immediately wipe dry. It always seems quite wrong to me to start sloshing water over a raw steel surface when you are trying to stop it rusting.

[rfs1957]

Couldn't agree more Hugo, about water, it doesn't make sense. Hence my frustration with manufacturers - see above - whose instructions are so incoherent. Any who when questioned in one-to-one exchanges cannot do any better.

Now, where is our brilliant chemistry student when we need him ?!

[chrisfell]

As the forum's chemist appears to be away, and my chemist left my employment about thirty years ago......

Wash with water to remove the phosphoric acid that has not converted iron oxide to iron phosphate. Wiping wont get it all away, and what is left will react with whatever paint is applied. Water is better. Wash with water and then dry. Dont leave water on the steel to create more rust.

[mgcjag]

Hi Rory.....have mailed Simon asking if he wanted to get involve but at the moment he is far too busy with his Studies.....there really is a big opening in the market if someone could come with an un ambiguous product.....Im still concerned that the Phosphoric acid leaves salts on the surface so i only use it in areas with no seams..then wash and scrub to ensure no salts remain...force air/heat dry then etch prime.....is this the best way...havnt a clue

[ralphr1780]

Will you tolerate a slightly older chemist in place of Simon?
From past experience: the phosphoric acid treatment is followed by short rinse with demi-water, then hot air drying, then priming.
The phosphates layer created after the phosphoric acid treatment is quite fragile and should not be disturbed with aggressive chemicals nor mechanical strains (= no wiping!) nor left unprotected.
Hope to have modestly contributed to the debate...

[Series1 Stu]

I've really enjoyed this thread so far. There are so many of us that have been messing about with old cars for so long and yet still nobody knows for sure the best or correct way to treat and prevent rust on steel. Well, that's not entirely true because, as a day job, I design metal structures for use in marine and submarine applications. The difference there though is we don't start with rusty metal and we give it lots of zinc before we paint it (if we paint it). We also have relatively generous budgets to work with.

We did experiment with electro-phoretic coating and the results were spectacular with no rusting of a steel panel that was left outside in the yard for over a year. It's a pity it isn't a simple enough process to do at home, although you can have a whole body shell done professionally.

This is a great debate.

[ralphr1780]

Stuart, the question was about phosphoric acid treatment and not about the best or correct way to treat or prevent rust on steel. That would be a totally different debate.

[Hugo]

Doesn't sound un-related to me - has anybody had a word with Frost auto-restorations? They seem to have some interesting products.

[Series1 Stu]

I don't think it's unrelated either and I asked the initial question. Forum threads often twist and turn away from the initial point but this one has stayed pretty much true.

I think the point about commercially available products is that there's a lot of hype surrounding them but little solid evidence of their efficacy.

The good news is that it keeps us in our sheds and garage the world over fighting the threat that is corrosion.

Regards

[david muir]

Currently de-rusting some Mini parts in 10 litres of vinegar-cheap as chips (Lidl) and effective. Still need to coat the steel quickly after removal/rinsing but that's no big deal.

[david muir]

Currently de-rusting some Mini parts in 10 litres of vinegar-cheap as chips (Lidl) and effective. Still need to coat the steel quickly after removal/rinsing but that's no big deal.

[Series1 Stu]

My heater box is next. I just need to find a vessel big enough but without being so big as to need lots of gallons of dip.

[Hugo]

I had some seriously rusted engine parts off a 1917 American LaFrance I am rebuilding. I dunked them in a mixture of caustic soda and some kind of dishwashing salts, hooked up a 12 volt battery with the pos connected to a sacrifical anode (big lump of iron) and the neg connected to the item to be de-rusted.
It floats the rust off & just leaves the steel. It won't hurt a plastic container, and I THINK it's ok with aluminium and other metals too.
I am not cautious by nature, but caustic soda is evil stuff. It dissolves skin, and while I could probably tolerate a few small splashes - skin re-grows - it also dissolves eyeballs immediately and they don't.

[mgcjag]

There are plenty of solutions that will remove rust....its whats left on the surface after thats of concer...ie Phosphoric acid will leave unseen salt.....if this isnt removed it will continue to corrode after you have painted....from what i have read these salts are extremely difficult to remove and just wiping or rinsing will not get them off.....

[Hugo]

Inside of sills etc I wouldn't bother with any kind of rust treatment - just fill it up with cavity wax so that it creeps into all the places that water will find. What I did on my wife's Morris Minor, to get right to the front of the chassis legs, I got an aerosol or two of waxoyl & spiked the can with a screwdriver - you get a high pressure jet of spray that will go quite a distance. You need a good aim or it can get quite messy though!

[chrisfell]

I got an aerosol or two of waxoyl & spiked the can with a screwdriver - you get a high pressure jet of spray that will go quite a distance. You need a good aim or it can get quite messy though!

Or you could have done what I did. I bought a simple spray gun designed for squirting waxoyl into cavities. Search eBay, there are plenty around, some hand held, some require a cyclinder to be hand primed, some attach to an air compressor. A lot less messy.