Do "Rust Converters" work as advertised

[cliff.b]

Seen several that say that chemically convert rust and form a "primed" surface suitable for painting. I used something like this about 40 years ago and the rust soon came back but wondering if they are better now.

Does anyone have any experience and if so, what is worth using?

Edited May 6, 2023 by cliff.b
Wrong word

[Keith Nock]

I use kill rust and found by accident that if welding a new panel to an old one with minor rust the kill rust gives a much better weld

keith

[trigolf]

Check out Rustbuster UK. I've no connection to them but have read very good reports about their products. Indeed I've just bought their Rustbuster Epoxy Mastic 121 two pack paint. They do a whole range of specific products.

[ed.h]

By far, the best rust treatment is removal. 

If that is impossible for some reason, you can try so called "converters" or "encapsulaters".  These generally do what their names imply, but the adhesion to the base metal still depends on the rust.

Ed

[daverclasper]

I do use the milky solutions that turn black, though only on the small pits that are often left after wire wheels etc have taken off the bulk and are not always easy to remove. Not had any obvious problems yet (started using it 10 years ago and car is outside all year round). Any primer I have used on top of converter, seems to adhere well.

I did find, if converter used on thicker surface rust it failed quite quickly. 

[JohnD]

All the "rust removers" or "encapsulates" are based on phosphoric acid.  This is a so-called 'weak' acid that attacks rust more than the actual iron.     But unlike every other acid, iron phosphate the reaction product is insoluble in water, so stays attached to the part, as a dark, blackish coating that is a good ground for primer.

You can buy concentrated phosphoric acid for about £3/litre.   Compare that with "rust removers"!

It doesn't work on thick rust - only the surface is attacked, so clean off rust mechanically before applying.

John

[ed.h]

20 minutes ago, JohnD said:

All the "rust removers" or "encapsulates" are based on phosphoric acid. 

John, there are two broad classes of chemical rust removers.  One is indeed based on weak acid, but it can be others beside phosphoric.  I've seen oxalic, citric, and gallic, but I do believe that phosphoric is the best.

The other class is chemical chelates.  These are usually close to neutral pH, and work by stealing and sequestering the iron from the rust.  EvapoRust is a chelate, but there are others.

A so called "rust encapsulator" may just be a very tenacious coating that isolates the rust from further moisture, but doesn't really do much chemically to it.

Marketing hype often makes it hard to know how a particular product works.

Ed

Edited May 6, 2023 by ed.h

[Unkel Kunkel]

The terms  are a bit confusing -  “ converters” are a different group to rust “removers” though some removers can to some extent, covert..and Loctite use the term “ neutralizer” for their  product * - which could be viewed as a “converter”

The removers include  acid groups as hydrochloric ( the archaic term muriatic acid is still used by some ) then phosphoric , oxalic acid ( poisonous) as  “strong” acids and weaker acids such as citric, and acetic acid, as vinegar.

The  converters are chelating agents - sort of binding agents that envelop the rust chemically and also provide a basis as a primer.

The most widely used seem to be tannic acid and sometimes a derivative , gallic acid. When mixed with a liquid polymer this enhances the primer action.This can be a latex solution. Sometimes some   dilute phosphoric acid is added to the mix to lower the pH for the tannic acid to work more effectively and for direct effects of the phosphoric acid.

Typically the tannic acid products goes blue /black after application to rust.

For success the instructions have to be followed :

1.They will fail if applied  on loose, flaking rust. 

2. The primer action only  works on the rusted metal.

Citrate is a bit of both, it works -as an acid -as  a remover and also has a chelating action.

Molasses is also chelating agent. It takes as long as months to work,  I understand.

Evapo-Rust composition is not revealed to us,  but its low toxicity, neutral pH suggests it is probably a citric acid based with  a chelating agent or several agents, ( other  than tannic acid). It is very expensive.

 

The advantage of converters include their ease of use and low toxicity( The worst thing that tannic acid will probably do is stain your fingers very black)

A lot depends on what is rusty and where it is.

The encapsulator paints can  work  for inaccessible bits.Their effectiveness depends on the integrity of the that sealing coat. I would suspect that any  defect in that coating,  whether on application or acquired later, can lead to   failure.

Ideally, If you can remove a rusty bit and can immerse it for a few hours then  go for any of the “remover”s.

(My choice these days is Citric acid for 6-12 hours at 50- 60 C,  in an ultrasonic cleaner, It cheap, very effective, safe to use and  dispose of afterwards) 

*  Loctite product recommend

Edited May 6, 2023 by Unkel Kunkel

[ed.h]

3 hours ago, Unkel Kunkel said:

Evapo-Rust composition is not revealed to us,  but its low toxicity, neutral pH suggests it is probably a citric acid based with  a chelating agent or several agents, ( other  than tannic acid). It is very expensive.

I've read some circumstantial evidence that EvapoRust is based on EDTA or something close to it, but with some trade secret sulfur compound that allegedly extends the capacity of the chelate.

Ed

Edited May 7, 2023 by ed.h

[PeteH]

Chemical science that goes with "Modern" corrosion treatment is way beyond my remit. But have used the old "waxoyl" with some success, providing it can be re-treated periodically. I have used Phosphoric acid with some success in the past, My "go to" especially for Alloys and S-S, is Citric acid for cleaning/descaling. (Made a Great job of the Old, Ex B-R Station, Copper Lantern which now graces the rear Yard.)

My experience beyond that, stopped with mechanical de-scaling and "Red Lead" Paint used on Ship`s Hulls back in time. Works on Car underbodies too!.

Pete

[johny]

15 hours ago, cliff.b said:

Seen several that say that chemically convert rust and form a "primed" surface suitable for painting. I used something like this about 40 years ago and the rust soon came back but wondering if they are better now.

First dont forget that the product is a sold as a 'rust converter' not a rust preventer. The second part had to be done by whatever you put over the treated surface and of course if that doesnt work well the original material will produce more rust!

I used one years ago and it certainly converted the rust into a hard black material but the amount of rust present made a difference. If the surface was cleaned too much then there wasnt much point putting the product on so it worked best if used on a layer of well attached rust.... 

[JohnD]

Gosh, thank you to all above who added to my education!    Sometimes this forum is like a University Common Room, with experts in every possible subject there!

John

[Colin Lindsay]

I use Jenolite, as I bought a huge container of it many years ago and it's still half full. I do clean the loose rust off and usually wirebrush the metal beforehand. If the part is small enough or removable, sandblasting works better although I cheat and use a rust-encapsulating paint over the blasted metal, I like the finish it gives compared to bog-standard grey primer.

 

[dougbgt6]

I use Bilt Hamber's  Hydrate 80, all the rage on the old forum. Goes on white and turn a very pretty pastel blue. Once a Practical Classics Best Buy. Expensive, but it works.

Doug

[Unkel Kunkel]

1 hour ago, Colin Lindsay said:

I use Jenolite, as I bought a huge container of it many years ago and it's still half full. I do clean the loose rust off and usually wirebrush the metal beforehand. If the part is small enough or removable, sandblasting works better although I cheat and use a rust-encapsulating paint over the blasted metal, I like the finish it gives compared to bog-standard grey primer.

 

Rust.

A subject  near to the hearts of old car enthusiasts especially old, old car enthusiasts !

I used Jenolite for many years, but I now  use a Machine Mart product which is very similar.Both are phosphoric acid.

Very effective, but unless just treating “flash” surface rusting i.e where the rust is deep, it best regarded a process  needing  repeated applications with chipping / wire brushing between each to get into the pitted areas.

Used patiently  in this way, it will certainly give excellent results.

It is more user- friendly  than hydrochloric acid. HCl   has nasty corrosive vapour. ( Leave something uncovered in it  overnight in your garage/ workshop and next day anything ferrous  in a 2 metre radius will have acquired surface rust).Not too kind  to your lungs either.

There is a theory that HCL shouldn’t be used on springs because “ hydrogen” brittleness” can result- making them more liable to break.This seems to be the case for small coli  springs like return springs on throttles and brakes, but whether it is a concern for car suspension springs, I have no idea.

 

The only differenceI I found is , as you can see, is that the MM version is much cheaper.

[GrahamB]

I too use the Clarke's phosphoric acid rust remover, mainly on small items.  Some is poured into a plastic pot and any rusty nuts and bolts placed in the acid overnight, then rinsed in water.  If the the hex is not too rounded, and the rust was only on the surface, I clean the threads with a die or tap and give a light spray of oil ready for re-use.  It works well.

[johny]

3 hours ago, JohnD said:

Gosh, thank you to all above who added to my education!    Sometimes this forum is like a University Common Room, with experts in every possible subject there!

John

Dont get too confident John as everything on here has to be taken as advice offered free with the corresponding disclaimer that sometimes it might not be correct😁

[JohnD]

That is true even of University Common Rooms!

[johny]

Dont think we're that bad!

[dougbgt6]

 I know very little about the majority of Triumphs, but a great deal about late GT6 mk3s, (after February 1973). Mainly because everything on mine has broken at least once since I bought it in 1978. 

Doug

 

[cliff.b]

9 hours ago, johny said:

First dont forget that the product is a sold as a 'rust converter' not a rust preventer. The second part had to be done by whatever you put over the treated surface and of course if that doesnt work well the original material will produce more rust!

I used one years ago and it certainly converted the rust into a hard black material but the amount of rust present made a difference. If the surface was cleaned too much then there wasnt much point putting the product on so it worked best if used on a layer of well attached rust.... 

I'm thinking of using something on suspension components and other parts underneath prior to painting and then applying Dynax UC. 

[johny]

I would think your components havent got enough rust on them for a converter to be much use. Of course powder coating of removable items is the best solution but otherwise maybe wire brushing and then Hammerite if its still any good these days...

[cliff.b]

Just now, johny said:

I would think your components havent got enough rust on them for a converter to be much use. Of course powder coating of removable items is the best solution but otherwise maybe wire brushing and then Hammerite if its still any good these days...

Yes, that's another possibility I was considering. Various parts of the suspension were painted when I bought the car but now coming away in places with rust underneath. Don't know what paint was used or what prep had been done, but want to do a better job of it.

[cliff.b]

6 hours ago, dougbgt6 said:

I use Bilt Hamber's  Hydrate 80, all the rage on the old forum. Goes on white and turn a very pretty pastel blue. Once a Practical Classics Best Buy. Expensive, but it works.

Doug

I was thinking if trying the Hydrate 80 as I am already using the Dynax 50 & UC. Are you happy with it?

[ed.h]

6 hours ago, Unkel Kunkel said:

There is a theory that HCL shouldn’t be used on springs because “ hydrogen” brittleness” can result- making them more liable to break.

 

Hydrogen embrittlement is indeed a real thing.  It really only affects hardened or spring steels, and exposure to acids or electrolytic conditions can promote it.  That's why it's important to know what's in a product before using it on susceptible metals.

Ed