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using phosphoric acid
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Lanchester 1953



Joined: 05 May 2016
Posts: 34

PostPosted: Thu May 12, 2016 6:23 pm    Post subject: using phosphoric acid Reply with quote

I have started de rusting with some phosphoric acid, but what is the right procedure?? do I let it dry and then paint, or wipe it with a wet cloth after it dries? should I dilute it? it is 80% and quite oily consistency . so far the rust has gone grey just like promised.
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MikeEdwards



Joined: 25 May 2011
Posts: 2463
Location: South Cheshire

PostPosted: Thu May 12, 2016 6:52 pm    Post subject: Reply with quote

I've always painted it on, let it do its stuff, wire brush it, then wash it off and dry with a heat gun if necessary. Often I'll have to wire brush and re-apply quite often, depending on how bad the rust spot is. I did some on a tailgate a few weeks ago, I re-applied probably four or five times but it went from a rust spot to a pitted, but perfectly clean, area.
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kevin2306



Joined: 01 Jul 2013
Posts: 1359
Location: nr Llangollen, north wales

PostPosted: Thu May 12, 2016 7:41 pm    Post subject: Reply with quote

I once had an old lister engine I was refurbing. Most of the bolts etc were crusty so I threw them in a bucket of phosphoric acid that I bought online, ready to use in a handy container.
Shortly after that I totally forgot about them until weeks after. Went to get them out to find the majority of the bolts had dissolved and were beyond use.
Great stuff but be careful and set a reminder somewhere

Kev
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colwyn500



Joined: 21 Oct 2012
Posts: 1745
Location: Nairn, Scotland

PostPosted: Thu May 12, 2016 10:47 pm    Post subject: Reply with quote

kevin2306 wrote:

Shortly after that I totally forgot about them until weeks after. Went to get them out to find the majority of the bolts had dissolved and were beyond use.
Great stuff but be careful and set a reminder somewhere

Kev


Kev, those bolts couldn't have been steel. Phosphoric is very effective and I think it is the best rust REMOVER, but it stops after the rust has been "eaten".
Mike Edwards describes exactly my experience. Even better is if the item is removable and can be dropped in a bath of diluted acid.
Currently I am dipping some extremely rusty cowlings for an air-cooled engine and whilst some holes are appearing in the sheet-steel pressings, this is because there is no steel left in a few pitted areas.
I would say this is the best discovery I ever made in car restoration, which is why I go on about it so much. Very Happy
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MikeEdwards



Joined: 25 May 2011
Posts: 2463
Location: South Cheshire

PostPosted: Fri May 13, 2016 10:04 am    Post subject: Reply with quote

I must say that when it comes to dipping removable parts, I've been using Citric Acid and I think (though I couldn't say I've done proper tests, as I'm trying to get stuff done at the moment, rather than experiment) it works better than Phosphoric. Funnily enough I've never tried using citric to paint onto panels - I did read once that mixing it with wallpaper paste powder makes it into a gel that can allow it to be used in that way.

I took some headlamps to be plated recently, and on discussing the rust removal the chap told me he used Hydrochloric to de-rust before plating, so once I've got a bit more time I'll be trying that.
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Lanchester 1953



Joined: 05 May 2016
Posts: 34

PostPosted: Fri May 13, 2016 10:16 am    Post subject: Reply with quote

colwyn500 wrote:
kevin2306 wrote:

Shortly after that I totally forgot about them until weeks after. Went to get them out to find the majority of the bolts had dissolved and were beyond use.
Great stuff but be careful and set a reminder somewhere

Kev


Kev, those bolts couldn't have been steel. Phosphoric is very effective and I think it is the best rust REMOVER, but it stops after the rust has been "eaten".
Mike Edwards describes exactly my experience. Even better is if the item is removable and can be dropped in a bath of diluted acid.
Currently I am dipping some extremely rusty cowlings for an air-cooled engine and whilst some holes are appearing in the sheet-steel pressings, this is because there is no steel left in a few pitted areas.
I would say this is the best discovery I ever made in car restoration, which is why I go on about it so much. Very Happy
that sounds a bit like when certain people have dunked stuff in a caustic soda bath, only to find it had vanished later! I knew a person who cleaned his paintbrushes in caustic. It will remove aluminium powder from files, though.
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kevin2306



Joined: 01 Jul 2013
Posts: 1359
Location: nr Llangollen, north wales

PostPosted: Fri May 13, 2016 10:49 am    Post subject: Reply with quote

colwyn500 wrote:
kevin2306 wrote:

Shortly after that I totally forgot about them until weeks after. Went to get them out to find the majority of the bolts had dissolved and were beyond use.
Great stuff but be careful and set a reminder somewhere

Kev


Kev, those bolts couldn't have been steel. Phosphoric is very effective and I think it is the best rust REMOVER, but it stops after the rust has been "eaten".
Mike Edwards describes exactly my experience. Even better is if the item is removable and can be dropped in a bath of diluted acid.
Currently I am dipping some extremely rusty cowlings for an air-cooled engine and whilst some holes are appearing in the sheet-steel pressings, this is because there is no steel left in a few pitted areas.
I would say this is the best discovery I ever made in car restoration, which is why I go on about it so much. Very Happy


they were old but being engine bolts I dont know what they were made of.
it was quite funny at the time to be honest

kev
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petermeachem



Joined: 23 Sep 2013
Posts: 358
Location: Chichester Sussex

PostPosted: Fri May 13, 2016 2:45 pm    Post subject: Reply with quote

Phosphoric stops metal rusting until you get round to painting. Mine has been sat in the garage for a year or more, hopefully my health will improve to the point where I'll be able to progress it.
I used something called milkstone remover, used in dairies and very cheap from agricultural suppliers. Also does a cracking job on the kettle
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Kleftiwallah



Joined: 27 Oct 2016
Posts: 222
Location: North Wiltshire

PostPosted: Sat Apr 15, 2017 1:27 pm    Post subject: Reply with quote

I was restoring my 1st Bonneville and I threw bits of carburettor in phosphoric acid. The following day there was just an assortment of brass fittings among the grey sludge! Embarassed BEWARE

Cheers, Tony.
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47Jag



Joined: 26 Jun 2008
Posts: 1480
Location: Bothwell, Scotland

PostPosted: Sat Apr 15, 2017 1:55 pm    Post subject: Reply with quote

Even molasses (treacle actually) will chew through steel if left long enough. I used a newish wood chisel to scrape crud off and I dropped it into the soup. I forgot all about it until the following spring and was draining the container when out fell a gnarled i.e. eating of metal with a plastic handle that I recognised. Shocked

Art
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OuBallie



Joined: 02 Mar 2013
Posts: 225
Location: South Norfolk next to Suffolk

PostPosted: Sun May 28, 2017 2:21 pm    Post subject: Hydrochloriic fumes WILL rust bright metal Reply with quote

MikeEdwards wrote:

I took some headlamps to be plated recently, and on discussing the rust removal the chap told me he used Hydrochloric to de-rust before plating, so once I've got a bit more time I'll be trying that.


Mike,
Plus anyone else thinking of using this acid.
PLEASE, PLEASE DO NOT! use the stuff in an enclosed area as the fumes WILL RUST bright steel overnight.
I found this out to my cost in the 1970s, when every one of my machine tools was covered in surface rust, when I was dipping parts in the acid, in the garage.

Geoff - Mud Shields repaired, photos soon.
_________________
Too many hobbies, not enough time!
1935 Austin Seven Ruby ARQ
1957 Austin A35 2-door
1967 Morris Minor 2-door
2007 Fiat Doblò MultiJet (It carries the spares etc)
Model Engineering
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OuBallie



Joined: 02 Mar 2013
Posts: 225
Location: South Norfolk next to Suffolk

PostPosted: Sun May 28, 2017 2:23 pm    Post subject: Hydrochloriic fumes WILL rust bright metal Reply with quote

MikeEdwards wrote:

I took some headlamps to be plated recently, and on discussing the rust removal the chap told me he used Hydrochloric to de-rust before plating, so once I've got a bit more time I'll be trying that.


Mike,
Plus anyone else thinking of using this acid.
Please DO NOT use the stuff in an enclosed area as the fumes WILL RUST bright steel overnight.
I found this out to my cost in the 1970s, when every one of my machine tools was covered in surface rust, when I was dipping parts in the acid, in the garage.

Geoff - Mud Shields repaired, photos soon.
_________________
Too many hobbies, not enough time!
1935 Austin Seven Ruby ARQ
1957 Austin A35 2-door
1967 Morris Minor 2-door
2007 Fiat Doblò MultiJet (It carries the spares etc)
Model Engineering
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MikeEdwards



Joined: 25 May 2011
Posts: 2463
Location: South Cheshire

PostPosted: Sun May 28, 2017 6:58 pm    Post subject: Reply with quote

Thanks for the warning. I haven't got around to doing anything with it, or if I have, it's also good at wiping memories.
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Sun May 28, 2017 9:25 pm    Post subject: Reply with quote

Hi
Phosphoric acid can be used diluted to 40% to act as a rust converter. I use it on every bit of steel that gets painted, even steel that looks perfect, the link is to an MGA body shell that had been professionally stripped just a few weeks earlier, the point being that corosion starts straight away. http://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=6134&postdays=0&postorder=asc&start=15

I clean the residue (Iron Phosphate) off with panel wipe, as this also ensures any moisture is removed, and then paint immediately.

Don't leave it too long before painting; whilst the Phosphate coating will provide some corrosion protection, it is porous and moisture in the air will re-start the corrosion process , albeit slower and possibly not visible to the naked eye.

Dave
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Brad1380



Joined: 28 Mar 2017
Posts: 5

PostPosted: Mon Feb 26, 2018 9:07 pm    Post subject: Reply with quote

I derust in a tank with washing up powder & a 12V supply.

Works well, would post a photo but Photobucket is broken.
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