Citric Acid gel/paste for rust removal.

Includes sheet metal, rubbers, bumpers, badges and rust repairs.

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funkyscooter
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Citric Acid gel/paste for rust removal.

Post by funkyscooter »

A citric acid bath does a good job cleaning up rusty metal with a little bit of help from a wire bush. Wanted to see if there was a way to use it in a form that would allow it to be applied to large panels.

An internet hunt lead me to a British welding forum which suggested using corn flour to make a paste with citric acid and water.

So armed with a table spoon measure (Australian 20ml not US 15ml) and a measuring jug this is what I came up with.

Test 1 - Paste (small batch)
35 g Citric acid dissolved into 100ml warm water
1 3/4 tblsp corn flour dissolved into small amount of water to form paste and avoid lumps, then add to warm acid mix.
Heat to near boiling to form gel. Stir all the time as gel forms quickly. Remove from heat as soon as it starts to thicken. Happens almost instantly.

Applied to test area of the boot lid. It is thick and needs some sort of applicator (spoon).
Wire wheeled the test area first, then applied paste and covered in glad wrap. Used a small roller to help distribute the paste under the plastic.
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Left overnight, scraped off paste, saved in a jar, and wiped surface down with water several times to neutralise.
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Once over everything again with the wire wheel
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You can see the untreated areas, that was covered by the masking tape, contains a lot more surface rust than the acid treated sections.
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Had to go over all the other areas I missed with the paste which I managed to save enough of to re use.
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Scott
(Not so rusty) Ol' Rusty - FB/EK Sedan
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funkyscooter
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Re: Citric Acid gel/paste for rust removal.

Post by funkyscooter »

Test 2 Gel. (bigger batch)
70 g Citric Acid dissolved 200ml warm water
2 x tblsp corn flour dissolved into small amount of water, and heat as above.

Now onto the gel.
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Applied with a 30mm brush to the whole panel and covered with glad wrap.
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Three hours later
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The next morning. Gel has gone quite liquid under the plastic.
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Wiped down with water.
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Scott
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funkyscooter
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Re: Citric Acid gel/paste for rust removal.

Post by funkyscooter »

Looks pretty good, although deoxide reveals a few spots. Should have wire wheeled it again but was interested to see how it went by itself.
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To sum up, will definately do this again. For a heavy soak, the paste is the go, but for a general clean up, the gel does the job and is easy to apply.
Either way, it's not magic - you do still need to wire wheel it, but far less than if you did wire wheel alone. Also less chance of warping the panel with heat.

Here is the end result sprayed with easyphos for storage. Lets see how long it takes for surface rust to reappear.
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Scott
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Re: Citric Acid gel/paste for rust removal.

Post by In the Shed »

Good work Scott, you have great cooking skills there. Is the glad wrap to prevent the mix from drying out early thereby rendering it ineffective?

Regards
Stephen
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Errol62
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Re: Citric Acid gel/paste for rust removal.

Post by Errol62 »

Great stuff Scott. I've wondered if molasses could be used neat with the glad wrap. Also if leav g it on longer would be more effective. Particularly with molasses.

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Re: Citric Acid gel/paste for rust removal.

Post by funkyscooter »

Stephen - Glad wrap is to stop the mix drying out - same as you would if using paint stripper on a hot day. Not sure if it would render it ineffective but the lack of moisture would stop it 'soaking' into the rust.

Clay - interesting to see how molasses would work, but might be too runny. This stuff didn't move when applying and seems to stay trapped under the glad wrap - even on the steep angle of the boot. As for time, I can only go by my limited experience with parts in citric acid bath. I soak for a day, rinse, scrape/wire brush and repeat. Things that have been left to soak longer still needed to be wire brushed and repeated. So decided 24 hours is more than enough.

My original idea with the 4 boxes in the first picture was to test different amounts of time. But I started late in the day so I only tested panel 4 after 3 hours. I took about 70 photos of the whole process, most of them now make no sense to me so I did not share more than I felt explained the concept.

But to visually explain a little more, I present panel 4 ....

Here is panel 4 wire brushed
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Paste applied and wrapped - after 3 hours
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Scraped off the citric paste. Still a lot of surface rust so not long enough.
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Washed, wire brushed, and re applied the scraped off paste and wrapped. This is now 14 hours after re application.
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Washed again
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Close up.
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Quick go over with wire wheel - not to shabby.
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Scott
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ardiesse
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Re: Citric Acid gel/paste for rust removal.

Post by ardiesse »

Scotty,

You've intrigued me now. When I am cleaning flaky surface rust from bright steel sheet, I pour on Ranex rust converter, leave it to sit for a couple of hours, then follow up with a paint scraper and wire brush. So I am tempted to try cornflour or agar with rust converter. Plus the cling-wrap.

Rob
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funkyscooter
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Re: Citric Acid gel/paste for rust removal.

Post by funkyscooter »

Hey Rob, it is certainly a good way to make water based things thick. Let us know how you go.
Scott
(Not so rusty) Ol' Rusty - FB/EK Sedan
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