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Can red oxide primer be painted on to Rust?

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Simon Robinson 417/11/2021 19:27:47
74 forum posts

I’ve got a can of Wilkinson’s red oxide primer but it says on the label that rust should be removed with a rust remover before applying the primer.

I was under the impression that Red oxide primer could be painted on to rust unless this brand is just red paint and has no anti-rust properties?

(Im wanting to paint some unused Met spike posts that have gone rusty)

HOWARDT17/11/2021 19:37:13
900 forum posts
39 photos

You could but I doubt it would last long, better to paint over with a rust neutraliser like Kurust.

Tony Pratt 117/11/2021 19:37:28
1926 forum posts
12 photos

Rust isn't the most stable of substrates.

Tony

Tim Stevens17/11/2021 20:10:17
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1584 forum posts

The answer is Yes. But if you do it won't last long. There are a few fancy paints that will 'combine' with rust to form a strong layer, but red oxide primer is not one of them. The red oxide is in the paint, not on the surface.

But I'm not sure if there is anything special about Met spike posts that might offer a more hopeful or helpful answer.

Cheers, Tim

Lathejack17/11/2021 20:30:15
311 forum posts
329 photos

I used to buy a brand of paint called Comma Stop Rust which was a red oxide paint that did contain an addative that would treat and neutralise rust, the rust would turn black under the coat of red oxide. I have searched for it more recently but just cannot find it, so it may have disappeared off the market.

bobcha17/11/2021 20:45:39
9 forum posts
1 photos

Was watching bargain hunt today the expert bought a cast iron object which he described as having a wonderful rust patina.

noel shelley17/11/2021 22:32:35
1278 forum posts
21 photos

A 10% solution of phosphoric acid will turn the rust into iron phosphate which is insoluable in water and therefore stop the rust then you can paint it. As has been said you can paint over it (the rust ) but it won't last long. There are few paints that will work well over rust ! Noel

bernard towers17/11/2021 22:33:26
568 forum posts
109 photos

+1 for comma stop rust used to use it years ago really good. Did a test with it painting a piece of rusty steel and hung it outside, it was still there 5 years later doing its job but as you say can’t get it anymore.

pgk pgk18/11/2021 07:50:46
2549 forum posts
293 photos

Much may depend on your project. Last year I replaced the bed of my aged farm trailer with steel sheets from local scrappy, ran a wire wheel over it to clean off the surface and 2 coats of agricultural red oxide. It's had about a dozen loads of wood chip blown into it and similar crudely shovelled out as mulch for my fruit trees and bushes as well as being outside unsheltered for 12 months. It looks fine with hardly any visible scratches. I’m impressed but equally it'd be no issue to dosh it out again when it does show signs of wear. You can also get farm oxide in a range of bright colours to save bothering with other top coats. Call my lazy..

pgk

Adrian R218/11/2021 08:59:56
160 forum posts
5 photos

The paint that I buy from the local agri. supplier seems to go on better and last longer than anything from the DIY store so if you have one handy then go and see what they sell.

Many paints aren't what they were for environmental reasons - red oxide was originally red lead oxide, so I doubt the current stuff has much in common with the original apart from the colour.

Mike Hurley18/11/2021 10:04:10
305 forum posts
87 photos

Experts may contradict me, but my understanding is that Red Oxide primer is basically a substance containing very finely ground iron oxide ( i,e, basically rust ) that adheres to the oxide already on the metal surface ( not any heavy / loose / flaking rust ) and provides an even key for top coats.

I'm sure for specialist projects all manner of advanced chemical primers are available these days, but Red oxide is a good general purpose go to. What you don't want really is a super-clean, highly polished metal surface to begin with, as that won't aid ' stick '

noel shelley18/11/2021 10:23:59
1278 forum posts
21 photos

For highly polished see my post on polished brass 5 mins ago ! Noel.

Neil A18/11/2021 11:22:26
107 forum posts

One product I have used in the past with success before painting is "Jenolite Rust Converter". Not particularly cheap, but very effective. Seems to be based on lactic acid.

They also do other treatments for rusted surfaces, but I've not used those.

Neil

martin haysom18/11/2021 12:05:17
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88 forum posts

personally i think all these so called rust converters are just snake oil scratch the black surface they leave and you will see red rust still gnarring away at your steel

SillyOldDuffer18/11/2021 13:06:45
Moderator
8469 forum posts
1885 photos
Posted by Mike Hurley on 18/11/2021 10:04:10:

Experts may contradict me, but my understanding is that Red Oxide primer is basically a substance containing very finely ground iron oxide ( i,e, basically rust ) that adheres to the oxide already on the metal surface ( not any heavy / loose / flaking rust ) and provides an even key for top coats.

...

That's right, but there's less rust in it than might be expected.

Sometimes Safety Data Sheets reveal what's actually in products. Unfortunately, they're only obliged to reveal hazard content, which in the case of paint is usually the solvent and drying agents, which are likely to be inflammable, intoxicating, poisonous or a cancer risk. (Sounds scary but good ventilation de-risks home painting almost entirely: it's the bloke who does a lot of painting in a confined space who ends up with Emphysema 20 years later. Smoking multiples the risk because breathing through a flame modifies the fumes.)

I only found one SDS that listed the pigments in Red Oxide Primer. In this example, the main pigment is Calcium Carbonate (chalk), with about 10% each of Barium Sulphate and Red Iron Oxide. Barium Sulphate started in paint as a filler, but seems now to have more sophisticated functions such as improving spread, reducing fogging of the top coat, supporting high-gloss finishes, and reducing the amount of harmful solvents needed to get the paint to flow. Red Iron Oxide provides the colour, some anti-corrosion protection, and it resists ultra-violet light, which damages the long term stick.

Red Oxide primer is good stuff but it doesn't magically glue the soft loose flakes of a rusty surface back together. Best to remove loose rust with a wire-brush and to treat what's left with a Phosphoric Acid rust preventer. Rust preventers convert the rust into a stronger, more solid, water resistant form. Then apply red-primer to fill gaps and crevices to provide a good base for the top coat.

Note four different technologies each play a part in getting good results:

  1. Cleaning the base metal
  2. Solidifying any remaining corrosion with a chemical that inhibits further damage
  3. Filling gaps and providing a sun-resisting firm surface with a primer
  4. Protecting the primer and metal underneath with an attractive water-proof, knock-resistant outer

Quite a lot to go wrong in the preparation! Or in using old paint, mixing incompatible paint types, applying excessively thick layers, or missing bits. Not surprising paint jobs often disappoint : you can guess how I know slapdash application of left-overs and not reading the instructions is a bad idea.

Dave

Nigel McBurney 118/11/2021 14:33:18
avatar
999 forum posts
3 photos

difficult to find really good paint nowadays,too many of the chemicals have been removed by lobbying environmentalists, I restore stationary engines ,many have been really rusty,now for rusty metpostwhich were possibly orinally given a light galvanised plating,electrolytic rather than hot dip, the rusty areas would need to be thorougly cleaned,and the primer may not adhere for long to the plating. red oxide to my knowledge has never been suitable for painting on top of rust,its is used as a primer. now on steel which has shot blasted or thorourly cleaned with a wire brush two coats of red oxide is best,be aware that red oxide is usually matt finish,it is also supplied as gloss and I have when painting over the gloss finish with coloured gloss painted it is not very succeful. last year I bought two IDENTICALtins of red oxide from Brewers,one was matt one was gloss,just cnnot trust anything nowadays. On cast iron I clean off rust with a powerful rotary wire brush,then go over larger surfaces with an angle grinder,then paint with a well thinned red oxide so that it penetrates porosity and small crevices and then apply a thick coat to seal the surface, There used to be product called rustbeater a brown paint which could be applied over rusty surfaces afterloose rust was removed and worked quite well,the original manufacturer was taken over a couple of times and the later product was not very good.

Nicholas Farr18/11/2021 15:04:01
avatar
3310 forum posts
1524 photos
Posted by SillyOldDuffer on 18/11/2021 13:06:45:
Posted by Mike Hurley on 18/11/2021 10:04:10:

Experts may contradict me, but my understanding is that Red Oxide primer is basically a substance containing very finely ground iron oxide ( i,e, basically rust ) that adheres to the oxide already on the metal surface ( not any heavy / loose / flaking rust ) and provides an even key for top coats.

...

That's right, but there's less rust in it than might be expected.

Sometimes Safety Data Sheets reveal what's actually in products. Unfortunately, they're only obliged to reveal hazard content, which in the case of paint is usually the solvent and drying agents, which are likely to be inflammable, intoxicating, poisonous or a cancer risk. (Sounds scary but good ventilation de-risks home painting almost entirely: it's the bloke who does a lot of painting in a confined space who ends up with Emphysema 20 years later. Smoking multiples the risk because breathing through a flame modifies the fumes.)

cut

Hi Dave, while it is possible for someone in a confined space to suffer with respiratory problems, assuming it is small and with out adequate ventilation, it can also occur in an enclosed space like a cupboard under the stairs or any small space where fumes can't easily escape very quickly or have any means of being removed by extraction.

Confined doesn't mean small or enclosed, e. g. if you are inside a football stadium with all the exits closed and locked, you would be in a confined space even if it is open to the sky and therefore you cannot get out by conventional means. Prisoners are confined, even when they are outside but inside the boundary of the prison.

Sorry if I'm being pedantic, but don't like this word being used incorrectly.

Regards Nick.

Grindstone Cowboy18/11/2021 15:29:44
854 forum posts
64 photos

Not sure if it's still available, but Finnegan's Brown Velvet used to be quite good (probably similar to the rustbeater mentioned by Nigel). Used it on some already rusted pressed steel light fittings in an open seaside environment (50 yards from the sea) many years ago and they lasted quite well before the rust started showing through again - about three years.

Rob

Phil Whitley18/11/2021 19:02:55
avatar
1437 forum posts
147 photos

I think you might be over thinking this a bit chaps! No rust takes place unless oxygen comes into contact with ferrous metal, so remove loose rust with a wire brush, smooth with coarse emory tape or flap wheel and coat it up, if the oxygen is sealed away from the metal, rusting will not reoccur till the seal is broken. If you paint over rust which is rough, you will not get a seal, and enough oxygen will be contained within the rust for it to continue enough to break the seal and let the oxygen in again, remember that rust removers and rust convertors are not the same.

Phil

fizzy18/11/2021 21:04:21
avatar
1840 forum posts
120 photos

For clarity, brown rusting wont occur without the presence of oxygen (and water for most other types of ferrous rust, ( 4Fe + 3O2 + 6 H2O > 4Fe (OH)3 ( but once it has begun to rust the only way to halt the process is to either completely remove the rusting area or to treat it with a chemical with a lower state of oxidation - the best easily availible such chemical being zinc. Here zinc acts a sacraficial metal and oxidises instead of the metal. Not bad for over 30 years since I last thought about this!

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