Phosphoric acid ( flash rust )

[Myles1970]

Phosphoric Acid 85% - Food Grade Acid - Ecochem - Cleaning Products

Phosphoric Acid 85% Food Grade Acid – Biodegradable Phosphoric Acid removes water hardness, milkstone deposits and other oxide films safely when compared with alternative acids. Phosphoric Acid is especially useful for removing surface rust from ferrous metals and provides some protection...

www.ecochem.co.nz

…..don’t fear the flash

Honestly if you ask 5 different people you’ll get 8 different answers. At the end of the day it depends a lot on the time/resources at your disposal. You pays yer money etc.etc… blasting, acid dipping, electrolysis, wire brushing, bristle blasting all have their pros and cons. None of them are without their failings. You’ve, thus far, gone the power tool route of surface preparation coupled with phosphoric acid rust treatment (for the rust that survived your prep). The flash ‘rust’ that remains will aid adhesion to any subsequent coatings.

Good luck and keep up the excellent work

 

[vw1]

Again thanks for all your help and support everyone it's greatly appreciated and help like this is invaluable. I know I can be quite anal when rust is involved and I can only do the best with my what I have and can do.

Once again its much appreciated and thank you for your kind words on my restoration

 

[Ross365]

Is there a common definition of "flash rusting"? Back in the days when I was working, we had a customer who was very concerned about flash rusting of stainless steel after acid passivation. We had never seen it but he was very worried.

I take it to be a thin layer of powdery and loosely bound particles of rust tending to be quite orangey in colour, forming on a steel which has just recently been cleaned to a silvery finish by some means. I've never treated such a layer with phosphoric. I think that zinc primer paint "deals" with such a layer, but the more it can be removed, the better.

 

[Turbo]

Your are overthinking this!

A wipe over with celly thinners or panel wipe usually removes any flash rusting you get & you should be doing this anyway before painting it!

 

[vw1]

I had a my delivery yesterday. Came with all the data sheets and fancy pen and note pad. Very impressed I am with SML Paints and coatings.

 

[Pigeon_Droppings2]

After a good wash down with water the flash rust kicks in.

Been there...done that! My prep is mostly wire wheel....after the wire wheel I panel wipe and apply (1 part) epoxy rust converter which stays on the panel (doesn't need washing off). Then I put the 2 part epoxy over that.

Quite like the epoxy converters...it gives the steel some extra protection if the epoxy gets chipped off. I've no idea if this approach is "recommended" but its what I do and I'm happy with the results I get.

 

[vw1]

I know of rust converters the liquid that turns the rust black but not epoxy rust converter . You learn something new every day.

So I see dinitrol do one.

 

[Dcal]

The thing that is missing here is the surface profile of the steel.

I strongly recommend you attack the surface after you have cleaned it with 80 grit production paper. You maybe have already done it but it's hard to see in the photo.

This will scratch the surface and provide a grippy surface for the epoxy to bond to so it is not just relying on the chemical bond between the primer and the surface. (which is excellent for epoxy)
You are after a nice matte finish.

This is why blasting is such a good way to prep the surface.
Not only does it remove any contamination, it also provides lots of peaks and troughs and increases the surface area.
So for any given chemical bond, as the area increases so does the adhesion, this is without taking into account the mechanical grip which is huge.
Try and clean anything off a blasted, then a polished surface and you will see what I mean.

So for surface prep -

Blasting is best, but it is messy, has significant health dangers if not done properly and not everyone has the kit available for a one off job.

Final mechanical prep with a bristle blaster is next best, but it's slower, expensive for the kit and belts, hard to get into tight spots and who has a bristle blaster.

Sanding by machine or hand is a good option available to anyone and perfectly acceptable for conditioning a surface for Jotamastic 80.

The worst surface is one that has been polished with a high speed wire wheel or similar and the Jotun application guide tell you not to do it.
Wire wheeling is great for removing old coatings and rust but you really do need to do the final step of abrading the surface before applying the primer.

Apply all the converters and magic potions you like but do it after you sand, or do and then sand which will probably remove the converted layer so maybe pointless, but maybe better (if you know what I mean)

 

[Burdekin]

As above. The reason we use epoxies and epoxy mastics is that they bond extremely well to a well keyed and clean surface and they are anti-corrosive and water proof. Don't apply rust converters under your epoxy, it's just not needed and is a layer that can lead to the epoxy failing if the converter isn't properly bonded to the surface. The epoxy mastic will bond better than the converter and will prevent rust coming back through. Rust converters are fine for things where you want an ok life, you give it a wire brush, whack on some converter and then paint over but you're going to the effort to properly prepare the surface so you don't need converters or phosphoric acid. If you have prepped with 80grit or better and thoroughly cleaned with water and solvent based degreaser then you have a properly prepared surface for applying your epoxy. The same process as if you were doing the topside of the car.

 

[Pigeon_Droppings2]

So I see dinitrol do one.

I used to use Dinitrol rc900...but it's now expensive so I've switched over to Brunox which is basically the same but a little cheaper.

As others have said....if you can 100% prep the surface (preferably sand blasted) then the 2 part epoxy can go straight onto the prepped surface.

I've no intention of "justifying" what I do...it's an "at own risk" thing....but I've been very happy with the results. My prep is pretty terrible...I tried the wash off converters and had the same issue with flash rust.

 

[vw1]

The thing that is missing here is the surface profile of the steel.

I strongly recommend you attack the surface after you have cleaned it with 80 grit production paper. You maybe have already done it but it's hard to see in the photo.

This will scratch the surface and provide a grippy surface for the epoxy to bond to so it is not just relying on the chemical bond between the primer and the surface. (which is excellent for epoxy)
You are after a nice matte finish.

This is why blasting is such a good way to prep the surface.
Not only does it remove any contamination, it also provides lots of peaks and troughs and increases the surface area.
So for any given chemical bond, as the area increases so does the adhesion, this is without taking into account the mechanical grip which is huge.
Try and clean anything off a blasted, then a polished surface and you will see what I mean.

So for surface prep -

Blasting is best, but it is messy, has significant health dangers if not done properly and not everyone has the kit available for a one off job.

Final mechanical prep with a bristle blaster is next best, but it's slower, expensive for the kit and belts, hard to get into tight spots and who has a bristle blaster.

Sanding by machine or hand is a good option available to anyone and perfectly acceptable for conditioning a surface for Jotamastic 80.

The worst surface is one that has been polished with a high speed wire wheel or similar and the Jotun application guide tell you not to do it.
Wire wheeling is great for removing old coatings and rust but you really do need to do the final step of abrading the surface before applying the primer.

Apply all the converters and magic potions you like but do it after you sand, or do and then sand which will probably remove the converted layer so maybe pointless, but maybe better (if you know what I mean)

Thanks and yes I have not used 80grit on that photo but will and have done in the past . Thanks again.

 

[The Z'eer]

Recently, after a few applications of citric acid gel and mechanical abrasion (wire and flap wheel) the part I'm working on was ready for paint. I scuffed the surface with 120 grit, used the air gun for a clean up.

Then I used Rustbusters Phos Kleen B, I've previously tried just phosphoric acid but there were problems with the clean up afterwards. While the Phos Kleen was drying I prepared the Jotun 87. Once Phos Kleen dried, I then washed the bare steel with water and dried it immediately with clean cloths and hair dryer, no flash rust. On went the Jotun.

 

[Ross365]

So do Jotun say that the Rustbuster stuff is necessary, optional, or do they not mention it all? I wonder if they would suggest it should not be used . I'm very fond of the term "paint systems", viz, all the products come from the same company and are optimised for use with each other.

Re earlier comment that epoxy is water-proof, guess it depends on the definitions being used but I wonder if water-resistant might be more accurate? Water is permeable through all polymers, though some are much more permeable than others.

 

[fractured]

Then I used Rustbusters Phos Kleen B, I've previously tried just phosphoric acid but there were problems with the clean up afafterwardn.

Would it be possible to elaborate further about the problems you had with just phosphoric acid please? I am trying to understand the use of phosphoric so your experience would be interesting.

Many thanks.

Mick

 

[Onoff]

Bit of a media frenzy going on here...

 

[The Z'eer]

So do Jotun say that the Rustbuster stuff is necessary, optional, or do they not mention it all? I wonder if they would suggest it should not be used . I'm very fond of the term "paint systems", viz, all the products come from the same company and are optimised for use with each other.

Re earlier comment that epoxy is water-proof, guess it depends on the definitions being used but I wonder if water-resistant might be more accurate? Water is permeable through all polymers, though some are much more permeable than others.

Jotun don’t ever mention the automotive industry, it’s merely that we here have acknowledged the use for Jotun products for our hobbies. Jotamastic I believe is pretty much Rustbusters 121, at least that what I heard on here. 121 I think mentions the use of Phos Kleen or possibly phosphoric, I’ll admit my memory isn’t the best

 

[The Z'eer]

Would it be possible to elaborate further about the problems you had with just phosphoric acid please? I am trying to understand the use of phosphoric so your experience would be interesting.

Many thanks.

Mick

Of course, no problem

Neutralizing phosphoric acid...?

Using phosphoric acid minimally diluted with water for the removal of rust (pitted steel). It appears to work pretty well if left overnight...the problem arises when it comes to removing it. I was advised to use clean water with the addition of baking soda. I've scrubbed the steel with the...

www.mig-welding.co.uk

 

[Bluemotion]

This is true, but you are being just a little pedantic.
I did say the surface needed prepping, but you can start with a rusty surface.
You will never remove all the rust from rust grade A to D when cleaning to st2 (thorough hand and power tool cleaning) or even st3 (very thorough hand and power tool cleaning)
Picture below is of some rust grade D that I hand and power tool prepped last night.
The final prep was using a bristle blaster which is as good as you will get without blasting because it leaves a surface profile for the primer to stick to.

View attachment 367286

This still has rust, but it is more than good enough for an epoxy mastic primer.
Even blast cleaning to sa2.5 leaves some rust, for total removal you need to blast to sa3.

The surface tollorant bit is what tells you it can be applied over a less than perfectly prepaired surface and if that surface is steel it will certainly have some rust in it.

The application guide you refer to doesn't even mention rust after the prep has been carried out, but it does say to roughen the surface.
The reason I suspect it doesn't mention st2 or 3 ( which what is described in the text) is because there is no surface profile required in these specs which is super important.
The same document doesn't mention any chemical pre-treatments before applying the primer.

I didn’t know that all rust is graded like that. I’ve learnt summat new. Can you tell me how it’s graded and a description?

 

[Dcal]

Link below is a good place to start, there's lots of good information on the interweb but it's a big subject.

Surface preparation

www.steelconstruction.info

 

[fractured]

Of course, no problem

Neutralizing phosphoric acid...?

Using phosphoric acid minimally diluted with water for the removal of rust (pitted steel). It appears to work pretty well if left overnight...the problem arises when it comes to removing it. I was advised to use clean water with the addition of baking soda. I've scrubbed the steel with the...

www.mig-welding.co.uk

Many thanks for that. I have been cleaning the majority of rust through either electrolysis or grinding to bare steel where possible. The reason for the phosphoric is to try to neutralise the remaining rust and hopefully less likely to return after painting.

I usually wash the phosphoric off before it dries as once I left it on overnight outside and condensation made it go a bit scaley - which I then had to remove with abrasive so lots of additional work (which kind of cheased me off!).

I have had a bit of light flash rusting so I have used WD40 to remove the water as at the time I didn't have compressed air. It worked OK but if you planned to paint it you then had to clean off the WD40 which I used acetone and a tissue/rag.