[Busted Knuckles]

Pretty interesting article on the subject: http://www.hotrod.com/techarticles/b...removal_guide/

[deadbodyman]

Whats best in my opinion is use both together... blasting AND Ospho...
Its my opinion that even if you blast, the rust its still there on a microscopic level....The reason I feel this way is when a pitted piece of steet metal is blasted and set out in the weather unprotected ,the pits always start rusting before the unpitted metal...
Thats where the Ospho comes in...Imediately aftre blasting I treat the whole car and let it dry not only will it kill the rust on a microscopic level it'll protect any unrusted sheet metal from getting surface rust as long as the cars is in a garage surface rust wont ever be a problem.
Ospho is easy enough to use and "Does Not Need To Be Neutralized"

Blasting is a good way to remove rust but only if you take the car completely apart for a total restoration... chrome ,glass,REGULATORS,complete interior inc. dash,complete drive train....NO way you would do it on a car your driving and just doing a weekend floor job. Or a vinyl top repair job. Or even in places like a windshield frame only repair ,where its only pitted rust but its structurally sound the glass is out but it's a nice running car thats being driven ... no way you would want to blast there ....Sure You might be able to turn a minor in and out repair job into an unneeded,all out total resto but most guys cant or wont pay 50,000 and up and something that looks nice already.. Again thats where "Removing" rust with Ospho and wire wheels is the best way I've found..
Yes..I went out and bought a blaster in fact I have three blasters at my shop A big commercial which I seldom use ,a small pressurized one that I use rarely but twice as much as the big one,and the small recyclng spot blaster which I use a lot (I'm on my third one) it makes almost no mess....

So its like the old question :whats the best seam to weld? butt,spot or flange....The true and only REAL answear is there ALL the best... when used where they're supposed to be.....You need to know them all and where to use them...
Many pros CLAIM blasting is the ONLY and best way to remove rust and strip paint....
Well ,I'm a pro too ,35 yrs exp... and I say its absolutly not...I know rust,I'm from NY where new cars get holes within five years ,I work with it almost every day....Even if I blast a car it gets Ospho.
using them together is the BEST way .....but its rare that blasting is a good option.. and never EVER a good way for anyone but experianced professionals to strip paint with...and dont hire a a man that blasts bridges to do your car on the side either, get someone that does automotive blasting.....
If you want to blast some rust yourself ,I strongly suggest you only use a recycling spot blaster...anything else and you have a 90% chance of doing expensive damage to the sheetmetal...or a motor (that sand gets everywhere ,places you would never expect or even think of like defroster vents or the fan ,you would find out when your cars finished and your driving down the road and turn on the defrosters and get a face full of sand.
AS for stripping paint .....if theres to much paint to sand off fairly easy (with 80 DA and do a whole car in a day or two) chemical stripperis a very good option (mabee the best) especially for the non-pros that want to remove a lot of paint fast...... all you need to know is a few tricks and tips and anyone can do it quick,neat and fast....My wife can strip a car and do it well...
.......She anit a professional stripper either....

[John68040]

Originally Posted by Busted Knuckles

Pretty interesting article on the subject: http://www.hotrod.com/techarticles/b...removal_guide/

Rust Bomb sounds like the best option I've heard so far. Actually removes the rust and sounds like it's a thick enough gel to use on the floor from underneath the car.

[Powork]

also been using Ospho for years, depending on the job, but most any time on large bare metal areas with very light rust I will apply. I have found that you really need that light rust to convert/neutralize for a lasting coating.

[sumner41]

Originally Posted by John68040

So would you recommend stripping to bare metal, treating with phosphoric acid, then using epoxy?

Absolutely correct. Our world is filled with magic potions. To do metal and paint work CORRECTLY, one MUST understand chemistry and metalurgey. RUST IS A CHEMICAL REACTION. METAL PREP is the way to go.

[GypsyR]

Some lack of understanding here. I'm no paint and body guy but I know you don't "neutralize" acid with water (as keeps getting brought up). You can dilute it or rinse it away with water. To neutralize it you'd have to counter it with an alkali like baking soda or soda ash. In practice, the reaction between it and rust sort of "neutralizes" its acidic properties. (OK, not really neutralizes it. Re-read your old high school chemistry books for what is really going on.) The residue left after treating with phosphoric acid is mostly ferrous phosphate which has a mild rust retardent effect. Phosphoric acid combines so readily with water that any residue is easily rinsed away. As for whatever other additives may also be in the mix, I have no idea what they might be but I suspect it's best they be washed off. Scrubbed off, if need be. Below 94 degrees and once the water has evaporated out of it, fairly pure phosphoric acid returns to its natural state. That of a whitish solid.
Stuff like Ospho containing mostly phosphoric acid is meant to be a rust remover/metal cleaner. As such it pretty darn good stuff and has long been used by steel mills for that purpose. The rust "converter" stuff I've seen (and tried) is pretty interesting but is pretty much a band-aid. It stops the rust, for a while, and does a pretty good job of covering it up. Also for a while. Sooner or later the rust alway seems to come back through the "converted" area. Or did when I tried it anyway.

[Lizer]

Originally Posted by GypsyR

Some lack of understanding here. I'm no paint and body guy but I know you don't "neutralize" acid with water (as keeps getting brought up). You can dilute it or rinse it away with water. To neutralize it you'd have to counter it with an alkali like baking soda or soda ash. In practice, the reaction between it and rust sort of "neutralizes" its acidic properties. (OK, not really neutralizes it. Re-read your old high school chemistry books for what is really going on.) The residue left after treating with phosphoric acid is mostly ferrous phosphate which has a mild rust retardent effect. Phosphoric acid combines so readily with water that any residue is easily rinsed away. As for whatever other additives may also be in the mix, I have no idea what they might be but I suspect it's best they be washed off. Scrubbed off, if need be. Below 94 degrees and once the water has evaporated out of it, fairly pure phosphoric acid returns to its natural state. That of a whitish solid.
Stuff like Ospho containing mostly phosphoric acid is meant to be a rust remover/metal cleaner. As such it pretty darn good stuff and has long been used by steel mills for that purpose. The rust "converter" stuff I've seen (and tried) is pretty interesting but is pretty much a band-aid. It stops the rust, for a while, and does a pretty good job of covering it up. Also for a while. Sooner or later the rust alway seems to come back through the "converted" area. Or did when I tried it anyway.

THANK YOU. I've said the same thing here before, as well. Water itself tends to run a mildly acidic pH (around 6.8 if not ultrapure). Adding water to acid (note if you were in my laboratory you would NEVER be adding water TO acid) merely reduces the molarity of the acid. Weakening the concentration of the acid, yes, neutralizing it? Of course not.

[TARM]

I am brand new here but this topic caught my eye as I am about to deal with some surface frame rust and some very light surface rust on the back of a door panel and body support on a Excursion. I have read every post with great interest.

What I have gathered from reading everything here is the following:

I see little controversy on here that Ospho does a good job of protecting or converting rust.

It seems the main and really only point of contention is whether Ospho leaves an acid film or not. Now specifically to this thread its a bit more detailed. We are speaking specifically if there is an acid film left when following the direction and procedures as laid out by DBM.

Is there some reason you can not just use a 0-14 PH testing strip on the metal surface after all the steps DBM does prior to spraying primer and see what you get?

Seems like a really simple and 100% way to put this to bed. I can not see how there could be any argument if the PH comes back somewhere around in the middle of the PH range. A 85% Phosphoric acid solution has a PH of about 0.5 PH so we are not talking some small change here.

My bet is that there is a differnce between Ospho leaving a acid film after dry vs following DBM steps and procedures there is an acid flim left from Ospho once you reach the primer spray step.

Basically it seems to me there can easily be a difference between soaking the metal with Ospho letting it dry

Now ready for epoxy primer and checking the surface PH

VERSUS

Soaking the surface with Ospho waiting wiping away any pools or drips any excess at all with a towel.

Waiting 24hrs

Sanding or scuffing the entire surface

Wiping off clean with a rag soaked in wax & grease remover (I think this may have a big effect)

Allowing to dry

Now ready for Epoxy Primer and testing surface PH level.


Its seems pretty straight forward and definitive to me but I am about as novice to painting as can be. Tons of experience Hot Parkerizing/Phosphating firearm parts for years but automotive industrial painting and prep Nope NADA NOT.


This looks like a much better choice for a person like me than a first time hobbyist than many of the other options out there. It will allow me to do sections at a time as I can. I can get it into hard to reach areas as taking some of these body panels off is not possible and or way to much involved for a daily driver. I just want to put to be sure I will not find a rotted out body panel under the undercoating in a few years. I live in the mountains of VA ( well we call them mountains here on the east coast) so we see salt and wet salt solution road prep during the winter months. I need to get the under carriage exposed surfaces sealed from this attack as best as I can.


DBM,

I want to personally thank you for spending so much of your free time attempting to educate others on the system you have used and found to work well. I have found it very helpful. But then I am very good at following directions. LOL

[Lizer]

Originally Posted by TARM

Is there some reason you can not just use a 0-14 PH testing strip on the metal surface after all the steps DBM does prior to spraying primer and see what you get?

Yes; pH strips require full immersion in the solution for which you are testing the pH and they need to be completely wet. Touching it to the metal would not give you a good reading.

Seems like a really simple and 100% way to put this to bed. I can not see how there could be any argument if the PH comes back somewhere around in the middle of the PH range. A 85% Phosphoric acid solution has a PH of about 0.5 PH so we are not talking some small change here.

You're only looking at pH and not chemical compatibility.

Wiping off clean with a rag soaked in wax & grease remover (I think this may have a big effect)

You would have to clean the metal with wax and grease remover anyways. But it's nothing I count on to neutralize an acid.