[unstable]

Doing patch panels on my doors, and I want to paint INSIDE the door with Por15 or maybe Eastwood rust encapsulator...I have to do this PRIOR to welding the panel on because well...I won't have access to the inside of the door as well once I weld it together.

So is it OK to paint (allow it to dry of course) and then weld? Doesn't welding have a corrosive effect on the metal? Is this an issue?

please advise.

[willys36@aol.com]

It'll burn off the coating @ the blue line. That heat affected area will tend to corrode more quickly than bare metal anyway so it the area you need to coat the most. Are you sure you can't get to it from the holes on the inside of the door? I haven't seen a door yet where I couldn't get to the outside panel by some sort fo contortion or other.

[adtkart]

As much as I hate to agree with Willys, I haven't seen a door I couldn't get my hand into. I get cut by everyone of them, but can get my hand in them. You do need to protect it somehow to keep it from rusting from the inside out.

[unstable]

Well I do have some access to the inside of the door through the access area. I just figured I could do a more thorough job when I have the entire bottom of the door opened up. Being able to reach in through the bottom and do my business sure beats pouring a couple of gallons of something inside and trying to shake it around to get complete coverage.

[Hellzapoppin]

A lot depends on what type of welding you'll be doing. Will you be seam welding the patch panels? You may find it easier to joggle the patch panel edges and plug weld them. If you can plug weld them then you could try using Weld thru Primer prior to welding.

Hellz

[unstable]

I'm told by the welding gurus at hobart that Por15 is a fair product, and that it's basically a mix of Phosphoric Acid and paint. They said to forget about Por15, buy some Phosphoric acid, hit the rust with the Phosporic acid and paint....so that's the plan.

Not plug welding...but welding the panel. It's too late to change my plan of attack now. Besides, butt welds are better...no laps to traps moisture.

[willys36@aol.com]

POR15 is urethane, not paint. It doesn't 'dry' by evaporation of solvents, it cures. Evidence of that is that moisture from any source, even the air, will cure it in the can- urethanes are cured by exposure to water. I don't know about its phosphoric acid content (I doubt it contains phosphoric acid since that is aqueous based which is a no-no for urethanes) but the active part of the formula is urethane.

[unstable]

Willy's, here's the information the guy posted. He seems pretty well versed in rust removal...he actually has a 4 page thread going on using electric and graphite and some other crazy stuff to remove rust...anyways here's his input:

No problem at all with POR 15, other than it's the MOST OVERPRICED product on the market.

Without typing 6 graphs regarding what's wrong with the process, it's impossible to stop rust unless you deal with the rust in the microporoscity of the metal.

Let the doors sit a few days, then swab them liberally with metal prep containing phosphoric acid, available from body shop suppliers, and then paint with Rustoleum. POR products attempt to accomplish it all at once, and the paint drys before the acid has time to work.

Yup, I know they sell millions of dollars a year worth of POR 15, and it's still a poor substitute for proper procedure.

MORE

There are hundreds of products on the market based on Phosphoric acid that chemicly convert Iron Oxide to Iron Phosphate, FeO3. FeO3 is a wonderful form of iron oxide that is a bonding layed between steel and paint, as well as a fairly impervious coating that prevents Oxygen from acting with the steel to become RUST.
These products range from Permatex "extend" to old fashioned Naval Jelly, and are all doing the same thing, converting RUST to FeO3.
In recent years there has been a headlong rush to get everything done faster, so manufacturers have added Phosphoric acid to paints, such as the famous & overpriced POR 15 product line. POR puts a lot more money into advertising than they do product.
The universal truth about shortcutting the process timewise is that it only converts to a minor depth of the rust layer, so you have a nice looking paint job that will pop, technicly spall off in time. Fortunately for the manufacturers of this paint, most people who use it don't hang onto the product they used it on long enough for the spalling to occurr, so they highly recommend it.
New steel, such as car bodys is too smooth for paint to hang onto, so it must be etched. Metal Prep has been used for years to etch new steel. It then had to be washed off with water, according to the recommendation, and followed immediately with primer.
If you let the same new steel form a layer of rust, and then apply Phosphoric acid, the RUST will change to FeO3, and all you need do is scotchbrite it smooth, and paint with good quality enamel. If you aren't looking for a mirror finish, you don't even need to scuff the FeO3 layer down, just let it dry thoroughly and then paint it.
Another advantage to using Phosphoric acid over products like POR is that you can allow it to soak in and convert all rust, including rust in the microporoscity of the metal.
Phosphoric is a safe acid to work with in the concentration used for RUST conversion, 4 to 8% in water by volume. Read the contents of a can of Coke or Pepsi, Phosphoric acid is a large part of the product.
Farmers spray it on lettus fields to make lettus grow better.
You do NOT want to spray it from a paint gun, because it will burn your lungs and is painful. You also do NOT want to get it on Aluminum because Phosphoric dosolves aluminum.

I think that's about it...anymore input on this topic boss?

[crazy larry]

You need to do your welding first, then do what ever type of rust prevention suits you. but definately do the metal work first.

[troy-curt]

Unstable;
I`ve been in the business a long time,seen a lot of over rated products come and go. Por 15 is a very good product I also use a lot of corrlious (not sure of the spelling)from eastwood. I do know
that por15 will distory your lungs, you must use a good resperater. If you try to weld metel with it on the back side the fumes are as bad as fresh ones.

I am not familer with this acid stuff so I can`t say one way or the other. I`ll have to be shown.

Any weld through coating fumes are dangerious to breath.
Any of these type fumes, once breathed in ,never leave your lungs.
The doc. says that in two more years i`ll have to carry oxg. with me.It`s not worth it. HTH

Good Luck;
Troy;

[willys36@aol.com]

Unstable; Yes, I am very familiar with the chemistry of using phosphoric acid as a rust converter. Have used literally gallons of 'Metal Prep" type treatments. I even worked on an industrial process to "soften" water using phosphoric acid to remove calcium from steam generator feed water. It worked great in removing the calcium but the calcium phosphate precipitate was a mess to handle and the cost wasn't competitive with sodium zeolite (i.e., Culligan) softeners. Also have used Permatex Extend and Navel Jelly which I agree are just renditions of phosphoric acid. However, I believe, probably in ignorance, that POR 15 is not one of these. All of the above are disbursed in water, are water soluble, wash off with water, and will burn your hands (it's acid after all!) if you get it on them. POR15 on the other hand is hydrophobic - you need to use great care not to expose it to water. I can't conceive of how you would combine phosphoric acid into it without immediately initiating the curing process.

Also, get it on your hands and it is there until that layer of skin wears off, not unlike Gorilla Glue and other urethane wood glues. Once applied to the desired surface though, both the wood glues and POR15 benefit from exposure to moisture which enhances the cure.

Another difference is that the phosphoric acid/quality paint coating is very tough and sticks well but it can be chipped off with a little effort. The POR15 coating on chemically clean but slightly rusted steel on the other hand is virtually part of the metal. It absolutely won't chip off from striking it or bending it. It must be ground off to remove it.

[unstable]

well that's one hell of a testomonial Willys!

I myself have yet to use Por15, my only exposure to it is all of the reviews people here post.

Nonetheless, I picked up some metal etch tonight, and I'm going to try using it on the piece of the door I cut off...to see what happens.

With a little luck, either road I take will hopefully keep me from rusting out in the near future. I'll definately have to try Por15.

thanks for the information everyone.

[adtkart]

One thing I have found in the last year or so, is that there are a million people trying to get everyone using something different for rust treatment. There are new ideas coming out almost daily on how it should be done. Although I have my doubts on any way to permanantly stop rust, i would think anything that gets as hard as POR-15 reportedly does, would have to help considerably.

Sorry Willy, I know that this sounds like I am agreeing with you . Believe me, I am trying not to.

[willys36@aol.com]

Don't get me wrong, I am not particularly endorsing POR15. Right now I am not particularly happy with the stuff 'cause I have two totally hard cans of it on my shelf that froze up after one short opening. All I wanted to do is point out that I am pretty sure it is unique in that it isn't phosphoric acid based like all of the others on the market. i guess I will but pints from now on and maybe I will get happier with it! It reall does work if you can keep it from hardening in the can.

[troy-curt]

Willy; I`ve had the same problem with the black stuff.
My wife saves plastic jiff peanut butter jars for me, for storing paint. It has a better seal than the can, and you can see what condition the paint is in, also it wont break. It keeps por 15 better than the can. HTH

Troy;