Discussion
I have a fair bit of surface rust on my project car. Thankfully nothing else (yet)
I am going to deal with at least some of this myself. I am starting with the engine bay, as at least messing this up wouldn’t ruin the extrernal paint work.
I remember my dad using vinegar when I was a kid. Has anyone used this method themselves?
I am going to deal with at least some of this myself. I am starting with the engine bay, as at least messing this up wouldn’t ruin the extrernal paint work.
I remember my dad using vinegar when I was a kid. Has anyone used this method themselves?
I have used DeOx-C Gel. I can't recommend it enough. Paint it on, leave it overnight covered in cling film wash it off in the morning and the rust is gone. Its like magic. Use generously.
They also do a powder to mix into water which you can soak smaller parts in. Its very good stuff.
Made by Bilt-Hamber.
Ive used it for all sorts from taking surface rust off an engine, to cleaning up a steering rack or finishing off castings that have been sand blasted, but still have rust in the pits.
They also do a powder to mix into water which you can soak smaller parts in. Its very good stuff.
Made by Bilt-Hamber.
Ive used it for all sorts from taking surface rust off an engine, to cleaning up a steering rack or finishing off castings that have been sand blasted, but still have rust in the pits.
Just get a bag of Citric Acid crystals, dead cheap, and dissolve in warm water. Experimentation necessary to establish strength but perhaps one or two tablespoons to a pint for starters. Small things just leave in to soak for a day or two then wirebrush. Never used it on a panel but the clingfilm idea sounds good.
I've used citric acid for soaking stuff in and it works well. I'd heard of mixing it in with wallpaper paste to turn it into a gel, then apply and cover in clingfilm. For painting on to panels to get rid of small rust spots I've also used phosphoric acid in the form of "ph down", a hydroponics product. That also works well, I've used that on very pitted areas, along with a stuff plastic brush (old toothbrush for example) to agitate it, and got the area perfectly clean.
I am not a Chemist, but my understanding is that if you just use a weak acid, like citrate, it will take the rust off, but it leaves the surface activated, and so sensitised to re rusting. The proprietary stuff, like DeOx contains compounds that neutralise the surface and stop it rusting again as soon as you dry it off.
Ive also heard o f people dropping parts into a molasses barrel and leaving it over night. Which also works.
Ive also heard o f people dropping parts into a molasses barrel and leaving it over night. Which also works.
)Non-chemist here, but my understanding and experiences from an amateur restorer's viewpoint.
Phosphoric works well on its own for "pickling" bare metal and can be used to good effect cleaning rusted metal, despite the fact that some will say it is only a rust "converter" (which I believe is technically correct).
I have some (poor quality, recycled Russian) steel in my garage that I coated with 75% Phosphoric and left several years ago. Some pieces were left wet with acid and others wiped down after soaking for a while. None have shown any sign of further rusting or deterioration since then. The only visible difference between the pieces now is that the ones left wet have a grey, scaly appearance whilst the ones wiped down just look like bare metal. For reference, untreated bare metal would be completely coated in surface rust by now.
To properly clean rusted metal, you have to work the surface as you de-rust with Phosphoric as the reaction ceases once the phosphate layer forms on the surface (and untreated rust will remain underneath), however the phosphate that forms is quite soft and agitation with a stiff nylon or wire brush is enough to remove it and allow the acid to continue reacting with the rust underneath.
I find that, once the metal has been de-rusted, a good wipe down with a clean dry cloth to remove the majority of the acid is all that is needed and then allow the surface to dry naturally. It won't re-rust quickly as the tiny amount of acid left on the surface after wiping down "pickles" the surface and that ultra thin layer of phosphate is absolutely fine for further surface treatments - i.e. paint.
With regard to paint, I assume, but have not tested the theory, that metal treated as above might be less suitable for etch primers if the phosphate layer prevents the acid in the primer reacting with the metal surface?
I tend to use BH Electrox on treated metal and found the adhesion to be outstanding. On rare occasions when I have needed to remove it again (e.g. to weld) it has proven to be very well bonded to the surface indeed.
Apologies to the chemists for any butchery of the terminology in the above!!
Phosphoric works well on its own for "pickling" bare metal and can be used to good effect cleaning rusted metal, despite the fact that some will say it is only a rust "converter" (which I believe is technically correct).
I have some (poor quality, recycled Russian) steel in my garage that I coated with 75% Phosphoric and left several years ago. Some pieces were left wet with acid and others wiped down after soaking for a while. None have shown any sign of further rusting or deterioration since then. The only visible difference between the pieces now is that the ones left wet have a grey, scaly appearance whilst the ones wiped down just look like bare metal. For reference, untreated bare metal would be completely coated in surface rust by now.
To properly clean rusted metal, you have to work the surface as you de-rust with Phosphoric as the reaction ceases once the phosphate layer forms on the surface (and untreated rust will remain underneath), however the phosphate that forms is quite soft and agitation with a stiff nylon or wire brush is enough to remove it and allow the acid to continue reacting with the rust underneath.
I find that, once the metal has been de-rusted, a good wipe down with a clean dry cloth to remove the majority of the acid is all that is needed and then allow the surface to dry naturally. It won't re-rust quickly as the tiny amount of acid left on the surface after wiping down "pickles" the surface and that ultra thin layer of phosphate is absolutely fine for further surface treatments - i.e. paint.
With regard to paint, I assume, but have not tested the theory, that metal treated as above might be less suitable for etch primers if the phosphate layer prevents the acid in the primer reacting with the metal surface?
I tend to use BH Electrox on treated metal and found the adhesion to be outstanding. On rare occasions when I have needed to remove it again (e.g. to weld) it has proven to be very well bonded to the surface indeed.
Apologies to the chemists for any butchery of the terminology in the above!!
99T is quite right about phosphoric acid, but may I amplify what he says?
Any acid will eat away rust, but 'strong' acids, like hydrochloric or sulphuric will also corrode the bare metal.
A 'weak' acid, an organic one (in the chemical sense!), like vinegar (acetic acid) will attack the rust but have very little effect on bare metal.
Phosphoric acid, a weak, organic acid,is unusual as the product of the reaction is insoluble. A layer of iron phosphate is left on the surface when it dries, resists further rusting and is an excellent surface for priming and painting.
But, if there is a thick layer of rust, an acid with soluble products is more useful to help remove it and get down to the bare metal, so vinegar - but table vinegar is very dilute, a stronger solution would work better - or another acid, such as Citric or Oxalic. ll are available as concentrates on eBay. Phosphoric acid is available as "Milkstone Remover" at Famers Supply depots, they use it to clean their milking machines! And it's what gives Coke it's 'bite' - look at the contents list on the can!
Any acid needs care in use - rubber gloves, eye protection and good sense, but given that, phosphoric and citric are safe to use. Oxalic acid is present in some foods, and in excess can cause kidney failure. But wash your hands and any clothes you wear after using these acids.
John
Any acid will eat away rust, but 'strong' acids, like hydrochloric or sulphuric will also corrode the bare metal.
A 'weak' acid, an organic one (in the chemical sense!), like vinegar (acetic acid) will attack the rust but have very little effect on bare metal.
Phosphoric acid, a weak, organic acid,is unusual as the product of the reaction is insoluble. A layer of iron phosphate is left on the surface when it dries, resists further rusting and is an excellent surface for priming and painting.
But, if there is a thick layer of rust, an acid with soluble products is more useful to help remove it and get down to the bare metal, so vinegar - but table vinegar is very dilute, a stronger solution would work better - or another acid, such as Citric or Oxalic. ll are available as concentrates on eBay. Phosphoric acid is available as "Milkstone Remover" at Famers Supply depots, they use it to clean their milking machines! And it's what gives Coke it's 'bite' - look at the contents list on the can!
Any acid needs care in use - rubber gloves, eye protection and good sense, but given that, phosphoric and citric are safe to use. Oxalic acid is present in some foods, and in excess can cause kidney failure. But wash your hands and any clothes you wear after using these acids.
John
Interesting stuff, thanks.
I have some stuff that I've cleaned in citric acid, stuff like bolts and small brackets, which seems to be still quite clean after sitting in a plastic box for a few months while I decide it's warm enough to set my plating kit up again. But after they've been in citric, I tend to rinse in cold water, dry and wire-brush. I wasn't consciously doing it to stop the acid, more to not be handling stuff with acid on it, and also because sometimes if my acid is dirty the stuff will have a grey sludge on it and I can't tell if all the rust is gone until I clean that off.
I have some stuff that I've cleaned in citric acid, stuff like bolts and small brackets, which seems to be still quite clean after sitting in a plastic box for a few months while I decide it's warm enough to set my plating kit up again. But after they've been in citric, I tend to rinse in cold water, dry and wire-brush. I wasn't consciously doing it to stop the acid, more to not be handling stuff with acid on it, and also because sometimes if my acid is dirty the stuff will have a grey sludge on it and I can't tell if all the rust is gone until I clean that off.
Thanks this is all very useful.
So I can use citric acid or distilled vinegar to remove the rust, using wallpaper paste (with cling film if necessary) to stick it on if I want to leave it on for a while. Then make sure I remove it properly.
Then I can either seal with primer or actually then use phosphoric acid to remove any last rust and seal.
So I can use citric acid or distilled vinegar to remove the rust, using wallpaper paste (with cling film if necessary) to stick it on if I want to leave it on for a while. Then make sure I remove it properly.
Then I can either seal with primer or actually then use phosphoric acid to remove any last rust and seal.
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