Hello! Log in or Register   |  Help  |  Donate  |  Buy Shirts See all banner ads | Advertise on TheSamba.com  
TheSamba.com
 
Flash rust or Iron Phosphate?
Forum Index -> Body/Paint Share: Facebook Twitter
Reply to topic
Print View
Quick sort: Show newest posts on top | Show oldest posts on top View previous topic :: View next topic  
Author Message
VanMan2009
Samba Member


Joined: October 26, 2009
Posts: 166
Location: Seattle
VanMan2009 is offline 

PostPosted: Thu Apr 01, 2021 12:23 pm    Post subject: Flash rust or Iron Phosphate? Reply with quote

Hey paint and body people - did I screw up?
Image may have been reduced in size. Click image to view fullscreen.


Is this flash rust? I'm dealing with seam rust on a Vanagon Westy, here's what I've done so far:

1. Once the interior was pulled, I blasted the rust I could see with a HF blaster and fine coal media.
2. DA'd (actually it was a random orbital) 80 grit everywhere else.
3. Phosphoric acid (aka Ospho) with an acid brush into the seams, and on the rust pitting that the sander couldn't get to the bottom of.
4. Let sit overnight. In the morning, I applied more acid to re-wet. scrubbed with a scrub brush, rinsed. scrubbed again, rinsed. wiped with clean cloth.
5. I then 'steamed' the treated areas using a hand held clothing steamer. (this was a recommendation on the Vanagon board to further neutralize the Ospho). Wiped down again.
6. Let try overnight, woke up to the above.

To test, I hit this area with the 80 grit again and it's mostly bare metal, but I can see tiny tiny traces of the gold color still there. Is that rust? Or is that the Ospho coating, and is it ok?

My next step is to encapsulate the seams with Eastwood rust encapsulator, and then prime using epoxy primer. I'm worried I won't get good adhesion, depending on what this stuff is Sad
Back to top
View user's profile Send private message Gallery Classifieds Feedback
infiniteLoop
Samba Member


Joined: October 09, 2020
Posts: 265
Location: Empire State
infiniteLoop is offline 

PostPosted: Thu Apr 01, 2021 3:51 pm    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

I would use a weaker solution of phosphoric acid on it,30 percent or less. After a few minutes wash it with very sudsy hot water and then hot water. Then I would dry it as fast as possible with a fan or a heat gun. After I was sure no moisture was present , I would prime it. And yes that is rust.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
raydog
Samba Member


Joined: February 09, 2006
Posts: 1157
Location: Cape Cod
raydog is offline 

PostPosted: Fri Apr 02, 2021 5:16 am    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

Using steam to neutralize? Never heard of that one before, isn't that just asking for problems? What are the benefits?
_________________
Come on, It's not rocket science. KISS
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
beetlenut
Samba Member


Joined: May 27, 2009
Posts: 2980
Location: RI
beetlenut is offline 

PostPosted: Fri Apr 02, 2021 6:20 am    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

Ospho doesn't need to be neutralized! Phosphoric acid, which is its primary ingredient, is like an atomic primer.
_________________
scrapyards are for quitters
---------------------------------------
Wetstuff wrote:
... I spend more time shaking it than directing it?! I get a pretty decent blast for 8sec. then have to shake it again.
- Words to live by right there!

My 74 Super rebuild thread: http://www.thesamba.com/vw/forum/viewtopic.php?p=6507104#6507104
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
VanMan2009
Samba Member


Joined: October 26, 2009
Posts: 166
Location: Seattle
VanMan2009 is offline 

PostPosted: Fri Apr 02, 2021 11:47 am    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

Quote:
Using steam to neutralize? Never heard of that one before, isn't that just asking for problems? What are the benefits?

Maybe? Laughing I heard the recommendation from a few guys on the Vanagon forum who are more experienced with this stuff than I am, but that doesn't mean they're right. The main idea is the steam can get into the crevices to neutralize the acid 'better' than just rinsing can, but again maybe that's bad advice.

Quote:
Ospho doesn't need to be neutralized! Phosphoric acid, which is its primary ingredient, is like an atomic primer.

This is definitely not what I've read, but I do think it matters what primer and paint you're using. I'll be using epoxy based primer, as I've read that's the best primer to use to seal the surface (and any tiny microscopic rust) underneath and keep moisture from getting in and causing more rust.

I think an etching primer or similar would likely be fine over Ospho? Here's a thread that covers the issue with epoxy primers:
https://www.hotrodders.com/threads/ospho-factory-response.173513/

Now that it's been one more day I can definitely confirm this is flash rust in my picture. My new plan is to re-sand DA 80 grit everywhere, wipe down dust / surface. Add diluted solution of acid and proceed as infiniteLoop suggests:
Quote:
I would use a weaker solution of phosphoric acid on it,30 percent or less. After a few minutes wash it with very sudsy hot water and then hot water. Then I would dry it as fast as possible with a fan or a heat gun.


I think my biggest mistake was getting the surface mostly dry, and then leaving it to air dry the rest of the way. I also didn't use hot / soapy water the first time, although obviously I got the acid off well enough, otherwise it wouldn't have flash rusted.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
bomberbob
Samba Member


Joined: May 17, 2015
Posts: 688
Location: Iowa
bomberbob is offline 

PostPosted: Fri Apr 02, 2021 11:57 am    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

If you are interested i preventing rust, search on "Masterseries Silver". Its good stuff.
_________________
1968 Beetle (storage)
1990 Jetta GLI megasquirted, burning E85 (currently in heavy maintenance)
2004 Jetta turbo GLI
Marion, Iowa
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
beetlenut
Samba Member


Joined: May 27, 2009
Posts: 2980
Location: RI
beetlenut is offline 

PostPosted: Fri Apr 02, 2021 12:32 pm    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

Phosphoric acid converts iron oxide (rust, which is in an unstable form) to iron phosphate (which is a stable inert form) by adding a missing electron. Phosphoric acid is is not like muriatic acid or hydrochloric acid that must be neutralized. Once the missing electron is supplied to the iron oxide, the reaction stops. I used it all over my car after welding and metal work. Just wiped it on and let it air dry. Then I used all Master Series primers and top coats right over that.
_________________
scrapyards are for quitters
---------------------------------------
Wetstuff wrote:
... I spend more time shaking it than directing it?! I get a pretty decent blast for 8sec. then have to shake it again.
- Words to live by right there!

My 74 Super rebuild thread: http://www.thesamba.com/vw/forum/viewtopic.php?p=6507104#6507104
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
infiniteLoop
Samba Member


Joined: October 09, 2020
Posts: 265
Location: Empire State
infiniteLoop is offline 

PostPosted: Fri Apr 02, 2021 2:24 pm    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

I think the difference of opinion on Phosphatizing is based on if you have bare metal showing or not.

Phosphoric acid will indeed flash rust if let to dry. The higher the concentration of acid, the more it will flash rust. I believe the humidity makes it worse. If you apply a phosphoric acid water mix on metal ,it will leave a residue so I doubt it is good to paint over. Acetone has been recommended to me to be used after a phosphoric acid treatment. From my own experience, if the mix is over 45 percent acid , you will have lots of flash rust issues. It will break down rust faster at higher concentrations but you can't let it dry out.

The white area of the shroud is where it is dry. The rest I just re-sprayed.

Image may have been reduced in size. Click image to view fullscreen.


This is a shroud I was going to throw out but I could not find a decent one in the classifieds so I decided to see how it would clean up. Some of the spots are proving to be stubborn but after about a month, it's pretty clean.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
2type2
Samba Member


Joined: June 02, 2002
Posts: 969
Location: SW Colorado
2type2 is offline 

PostPosted: Sat Apr 03, 2021 3:36 am    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

Hmm, surprised this is being a problem for you. When I did my bus , anywhere that had bare metal just got treated with a 2" paintbrush and full-strength Ospho. I am in Florida where the humidity is usually 80%+ and it was weeks before primer went on it. Personally I experienced zero rusting problems, maybe because of full strength? Ospho will make a white crusty residue, but I found that wiping it with acetone or paint thinner was all that was needed to clean up before paint. Phosphoric has the benefit of being able to flow into crevices....Try it stronger?
_________________
"A life of peace and happiness depends on your own gratefulness"
Back to top
View user's profile Send private message Gallery Classifieds Feedback
viiking
Samba Member


Joined: May 10, 2013
Posts: 2666
Location: Sydney Australia
viiking is offline 

PostPosted: Wed Apr 07, 2021 7:06 pm    Post subject: Re: Flash rust or Iron Phosphate? Reply with quote

beetlenut wrote:
Phosphoric acid converts iron oxide (rust, which is in an unstable form) to iron phosphate (which is a stable inert form) by adding a missing electron. Phosphoric acid is is not like muriatic acid or hydrochloric acid that must be neutralized. Once the missing electron is supplied to the iron oxide, the reaction stops. I used it all over my car after welding and metal work. Just wiped it on and let it air dry. Then I used all Master Series primers and top coats right over that.


1. Rust is very stable. It is happy to keep growing and the normal atmospheric conditions with mild steel are always right to just keep on rusting. If you mean unstable from the point of painting, then yes, this is true.

2. Iron phosphate is more inert than other things , BUT it is NOT stable. Other chemicals can dissolve the iron phosphate just as easily as acid dissolves rust.

Any acid reduces (i.e. the opposite of oxidises) rusty steel. The only difference is in the speed of the reaction. A strong acid like HCl (Muriatic or Pool Acid) works much more quickly than acetic acid (vinegar) or citric acid (food acid) or phosphoric acid (Ospho). You could quite easily and more cheaply use HCl to do the hard rust removal. The reason that most people shouldn't is that they will not be able to prevent the by-products of HCl, notably NaCl (salt) from using a sodium based neutraliser.

For example, citric acid is used extensively in the treatment of stainless steel, particularly the food industry. Stainless steel normally has a protective oxide layer to prevent rusting and staining. After fabrication or welding, citric acid (or other proprietary acids) are used to remove the original oxide layer and providing a perfect reactive layer to reintroduce a new and completely covering oxide layer.

There is a simple high school chemistry fundamental called stoichiometric ratio. This gives the theoretical amount of one chemical (phosphoric acid) that is required to react with another chemical (rusty iron). Providing more phosphoric acid than is needed to reduce rust iron to iron phosphate, stops that reaction after either all of the acid or all of the rust is consumed, but leaves unreacted phosphoric acid to react with any subsequent chemicals like paint.

So some people will see additional white deposits (probably excess phosphoric acid) or staining which can either be flash rust or some sort of phosphoric acid side reaction with other things.

Some people will see little flash rust, others particularly in humid environments will see more.

My preference is to do the following.

1. Use phosphoric acid to treat the metal as per the instructions. I tend to use a 10% solution. Most are around 30% from the bottle.

2. Once the reaction has happened, copiously wash the treated area with water. Some commercial solutions will produce black-ish iron oxide but read the manufacturer's blurb.
Hot water is better because more of the by-products will dissolve in hot than cold. But it is not necessary. The use of steam as discussed in another post is an option but all that steam is, is very hot water. Cold works fine. Some manufacturers say to wash with dishwashing soap afterwards.These are bit alkaline so probably aids in diluting the acid.

People will immediately jump in and protest that we are now adding water into the mix and that will cause rust. If you leave it too long wet then yes, you will introduce flash rust.

3. Mix up a solution of bicarb of soda and continue to wash down the treated area. This is to neutralise any remaining acid. How much to use is the art. More technically minded people can use pH paper on the wash water to get an idea, but it is not really necessary.

4. Rewash the area with water to remove any remaining bicarb/acid. It should now be in a very reactive state. The bicarb provides a small degree of flash rust prevention. Many of the media blasters using bicarb will say that the solution they use will keep the steel from rusting for a period of time. However, for most of us, we should just keep going to the next step.

5. Dry the surface of the steel with whatever you have, then use a hair dryer/heater/hot air gun to dry off the remaining surface paying particular attention to seams of the steel. Heating up the steel with say a hot air gun will tend to push out any water in the seams anyway.

6. Remove traces of water with a solvent. I use methylated spirits (denatured ethanol) because it absorbs water and is much cheaper than acetone.

7. Paint immediately. That is within a short period of time i.e. an hour or so. If it is raining or very humid try and do this on a drier day. Remember humidity occurs in high temperatures just as much as in low temperatures.

8. If like many people you are repairing and rust proofing in sections or painting in sections you must protect the metal after rust converting. There are lots of products that can do this. My preference is to mist a coat of WD40 over all of the steel. This will provide the protection you need. Cheap and easy to use.

DANGER WILL ROBINSON!

People will now jump in and say not to use WD40 because it has silicone in it and will lead to fish-eyes. NO IT WON'T. WD40 has no silicone in it. You have more danger from leaving some car polish rags in the corner of your garage given the amount of silicones some of these contain.

A very highly regarded restorer here in Sydney of 356 Porsches uses this all the time and he regularly takes these cars to concours condition. Of course after using the WD40 and before painting, you need to remove the WD40 because of its oiliness. This is where you would normally be using a prep-solvent anyway like acetone. Or you could use gun-wash or any paint solvent that takes off oily residue.

For those of you that rely on some of those moisture cured polyurethane products like POR-15 or maybe MS as well, if it requires a metal prep stage after washing with a degreasing solution and before applying the paint, you are washing the metal surface with an etch solution of phosphoric acid anyway.

Everyone has a method and climatic conditions affect the propensity to flash rust. This is my method, others will have theirs.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Display posts from previous:   
Reply to topic    Forum Index -> Body/Paint All times are Mountain Standard Time/Pacific Daylight Savings Time
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

About | Help! | Advertise | Donate | Premium Membership | Privacy/Terms of Use | Contact Us | Site Map
Copyright © 1996-2023, Everett Barnes. All Rights Reserved.
Not affiliated with or sponsored by Volkswagen of America | Forum powered by phpBB
Links to eBay or other vendor sites may be affiliate links where the site receives compensation.