ACID TREATING - Crust/Rust to Primer

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raygreenwood
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ACID TREATING - Crust/Rust to Primer

Post by raygreenwood » Wed Feb 06, 2008 9:26 pm

The best and cheapest rust treatment is ospho (a phosphoric acid mis). It is Grind or sand away deep crusty rust.....or...use a mask and goggles....and 60-40 muratic acid (swimming pool acid @ $5 a gal)...and chemically dissolve all of the rust down to bare metal. Rinse all of the acid washed areas with huge amounts of water....then let it dry unprotected for a day or two in dry weather so it gets a light surface rust. Then paint it with Ospho and a brush.
The Ospho turns rust into iron phosphate....a bluish black oxide that will never rust again. But....iron phosphate is thin and will eventually oxidize off just by itself....unless oiled or primed. If you prime or paint it it will preserve for ages. Iron phosphate makes a killer primer.....better than almost anything but zinc chromate. Once its airtight this stuff is rust proof. Ray

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MNAirHead
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Post by MNAirHead » Thu Feb 07, 2008 12:03 pm

Ray...

This is an important topic... can't tell you how much this has saved me over the years.

I actaully have a car that's 100% covered in Crusty rusty.. I can take pix and post.. It looks worse than the Jesse James crustbug.

I'd like to follow your suggestions exactly to the T
  • 1-WHAT dilution do you use for the Miratic Acid..
    2-HOW do you dilute it?
    3-CONCRETE - does this etch concrete the same way Phosphoric acid does?

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raygreenwood
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Post by raygreenwood » Fri Feb 08, 2008 7:25 pm

Ok....muratic acid (which is simply non-technical grade hydrochloric) will work on very light rust at anything above about 30%. Many machine shops keep a barrel out back of 100%. It strips rust from parts so fast that they fizz. But....keep the concentrtion at about 70% or less for rusted engineering type steels....like high grade moly. There is an issue with what they call hydrogen imbrittlement of the surface that can sometimes happen.

So for cast iron and sheet steel with rust.....100% or 60-40 or 70-30. It depends on how fast you want it to work...and how crusty it is. For really crusty sheet metal that is hard to reach with drills and brushes....I use 100% acid with a brush.

WARNINGS:

DO NOT let this stuff get on concrete. It will eat it for lunch. Keep a running hose handy.

Also when using this in the floorboards...
  • keep the car outside,
    the doors open with cross ventilating fans....
    and use diluted acid...
because as this stuff works...it smokes. If too much of that smoke/vapor gets around things like electronics....it can condense and over a long period of time...corrode things.

After you have stripped hard to reach places....rinse them carefully regardless where water flows to. You may have to dry hings out....but no big deal....because the surface rust that will be created....even in hard to see or reach places..... is your friend. The light surface rust the moisture creates is what creates the excellent material for the phosphoric acid treatment to convert to iron phosphate to make it RUST PROOF.

YOU MUST USE
  • goggles
    gloves (nitrile)
    and a respirator mask.
The cartridges in the respirator MUST MUST MUST....be listed as OVP-100/200 type. The operative color is pink and yellow or pink and olive color code. This stands for organic vapor AND acids. They cost the same as others...just dfferent.

MIXING WARNING
Always mix acid into water....NOT water into acid. This is because if the water's PH base is way to "base"....it can fizz and flash back on you so quick....you can get sprayed.

Mixing Instructions
  • Take a gallon bucket...
    fill with a quart of water
    slowly pour in a quart of acid for a 50/50 mix.
Wash all spills with at least 50 times their volume of water. This is mainly to dilute the acid before it gets to the sewer system. Thats not much. You spill a quart....use 50 quarts of water.

GAS TANK PREP & LINING
This method of rust removal works fabulous and is also really the operative system behind POR-15's gas tank treatment....if you read all of their ingredients.

You can acid wash the tank with 50/50 acid or stronger. Then....rinse copiously....then....let it surface rust inside for several days. You may even need to re-wet with water. Then slosh it around with phosphoric acid solution......twice.....letting it dry for 24 hours at least between.


After that....the view through the holes...of the inside ...which should have been lightly surface rusted....should be blackish/bluish...almost flat black and powdery looking. Perfect primer for POR-15 or any of the other expoxy treatments.

POR's stuff works. I think that others have had less than stellar results sometimes because the chemical solutions of the phosphoric acid and the acid etchant they use are slightly lower solution strength than I am using. They require proper time and agitation. People get in a hurry.

NOTE Do not get the acid on aluminum or magnesium....or its gone.

Ray

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MNAirHead
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Post by MNAirHead » Fri Feb 08, 2008 8:09 pm

Thank you Ray.

Over the next few months, I'll be working a shell... will be take pix and do extensive question and answer.

Hoping this helps some folks.

Chemistry question.
Is there a neutralizing process... meaning is there an alkaline mix we use when the reaction should stop?

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raygreenwood
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Post by raygreenwood » Sat Feb 09, 2008 9:56 am

Neutralizing answer....yes! Simply put, any solution that has both a high solution strength and a high PH will work as a buffer.

DO NOT....use baking soda and water. The main reasons are:

(a) if you somehow accodently slosh some of this baking soda/water solution into your acid vat it will react very violently and may end up spraying all over you.

(b) It has salt in it and will end up being a long term rust problem you can't fix.

If you need to be sure to stop the reaction of the acid quick there is a product I can recommend.
It is call Nutralyze. It is a detergent and industrial degreaser that is used by the screen printing industry for the degreasing phase of their screen reclaiming. It is also better than simple green for degreasing floors and parts. Its is less than $20 a gallon at many screen printing supply houses across the country. It is made by a company called CCI (chemical consultants inc). You can find their dealer listing at ccidom.com .

It works because its solution strength is high and its PH is about 7.0. It is designed to nutralyze and rinse away the heavy caustics used in "dehazing" screens (sodium hydroxide is our primary caustic)
For basic degreasing....or for this work it will work diluted at about 25:1 or 30:1. Very economical.

But again you need to flush with large amounts of water. Since we are trying to promote surface rust after "de-crusting"....so the Ospo will work, you can use water just fine.

Another good safety tip is to keep a bucket of nutralyze around at about 30-40:1 dilution. If you get acid in your eyes or on your skin or spill it one something critical....splash this stuff on. Even in your eyes. Its non-toxic and nutralyzes acids. Ray

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MNAirHead
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Post by MNAirHead » Mon Feb 11, 2008 12:27 am

So basically you're suggesting an alkaline industrial cleaner to neutralize the surface.

This may be overkill.. but does it make any sense to use litmus paper to check the surface pH?

T.

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raygreenwood
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Post by raygreenwood » Sat Feb 16, 2008 8:45 am

Not really because the problem that litmus paper deal with...is solution strength.

For example ...you could have an acid solution that reads 1.5 to 2.0 Ph.
This solution may be made of 1 part acid and 1 part water (50/50).

Then you can have a solution made of 3 parts water and 1 part acid.....and still....the litmus will read 1.5 to 2.0 ph.

This is because the solution strength of the acid is very high. You will have to dilute it many times with water to read anyh higher ph. By that time it will be diluted way past the point at which you can get a fast rust stripping reaction.

As you will note from the mixing dilutions of the degreaser I recommended, it has a very high solution strength. It can be diluted like 30:1 or more. Yet its steady state ph is a neutral 6.5-7.0 already. Plus....its got a rinse additive or surfactant that helps is rinse off...so even if you are using it at a 1:1 ratio it will not take gobs of water to wash off.

The reason I don't like products like simple greeen is that they are more expensive....and not quite so neutral in ph and many have sodium or silicates which are uglier for the purposes we are using them for. They leave residues that may mess up things like the phosphoric acid. If you can't get a soap or rinse additive you are sure of...just use water.

But.....any degreaser that has a neutral ph out of the bottle ...as read by test strip ...will do. Make sure the ph is not over 7.5. Ray

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InaneCathode
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Post by InaneCathode » Mon Feb 25, 2008 1:42 am

I always keep a full spray bottle of baking soda mixed with water as a sort of acid-extinguisher. Just spray like mad on whatever you spill the acid on, fizzes up and neutralizes the acid in seconds :)

I use muriatic acid to clean gas tanks of rust as well. Works WONDERS on the nasty scale crap in old motorcycle tanks.

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MNAirHead
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Post by MNAirHead » Mon Feb 25, 2008 11:10 am

Good idea on the neutralizer.. I screwed up a garage floor once by etching it

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MNAirHead
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Post by MNAirHead » Mon Feb 25, 2008 11:21 am

I should be ready fairly soon to begin the testing on this.

Spent a few hours yesterday removing the scale-rust with one of these

Worked great on fillers

Image

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MNAirHead
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Post by MNAirHead » Mon Mar 10, 2008 11:40 pm

So here's an update.

I went to the hardware store and bought 1/2 gallon of "Muratic Acid" for $2.39.

Yesterday sand blasting was a waste of time.. couldn't get a hold on the gunk. Had 2 backing plates that need some prep.. rusty 67s

I got a 5 gallon pail.. mixed 1 gallon 50/50.. plunked in the 2 backing plates.. cylls and all. The cylls were totally rusted immobile... within an hour I could pull out the centers..

After a few hours I couldn't tell the difference between the backing plate I spent 30 minutes trying to blast and the other one that had zero prep.

They're back in our warehouse soaking..

Will post back results after a bit.

t.

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MNAirHead
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Post by MNAirHead » Tue Mar 11, 2008 2:20 pm

Ray ..

This totally freakin rocks!

Dropped 2 backing plates in a gallon of 50/50 HCl.. they're clean.. not knowing if the acid was yet inert (had magnesium on the rusted brake cylls).. I droppped in some random super beetle backing plates.

I now feel like an idiot for wasting 6 hours this weekend blasting rust and crust off some suspension parts.



QUESTIONS
  • -Why do the HCl Bath parts rust soo quick - just flash rust.

    -Would it make any sense to store the newly "derusted" parts in some type of liquid solution to keep them away from air?

    -What point do I have to worry about hydrogen embrittlement and other structural issues?

    -Any tips for body panel use.. soaking isn't a real option.. wetting rags?

    -Chemistry 101.. If I'm guesisng right.. what's going on is FeO2 + HCl.. what inert and stable chemistry are we creating.

    -When do I know that the solution is tired and should be disgarded.

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raygreenwood
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Post by raygreenwood » Fri Mar 14, 2008 7:49 am

The hydrogen emrittlement worries are usually at higher concentrations and only on stressed parts and engineered steel like alloys. I would avoid sway bars could I just don't know yet.
If you throw something rusty in and it does not fizz any longer....its pretty dead.
The metal rusts faster because (a) there is now "0" oil/protection on it and (b) there is now lots of extra oxygen at the surface from the breakdown of the hydrochloric acid. I will get theexact chemistry for this and post it.

It rusts the same as when you pull a cast iron block or heads out of a caustic bath at the machine shop. There....they first get rid of excess water with an air hose and then immediately have teh squirt bottle of non-aerosol WD-40 handy to drive away water a neutralize everything.

What I recommend instead...is to let it flash/surface rust. Let it dry. Then hit it with Ospho. That makes the BEST primer hands down. That surface rust will convert and not rust again. The resulting black oxide is superb primer and protectant. Ray

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MNAirHead
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Post by MNAirHead » Sun Mar 16, 2008 10:26 am

Thank you.. I'll get some pix and post.. this may be the new trick vs using a blast cabinet.

Tim

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Daniel G
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Post by Daniel G » Mon Mar 24, 2008 12:56 am

Is there any certain paint that needs to be used over the Ospho coating? Will Rustoleum oil based paint work out ok? On my '71 panel, there is a lot of surface rust on my frame and suspension that I need to do something about before it gets any worse...I plan on stripping it down in a couple years and completely restoring it underneath and repainting or coating it with something good. I need a short term solution to stop the rust from getting any worse, and I was thinking that the oil based paint might work for now...But what do you think?

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