Dressing Welds Question

SP2 · 05-03-2009, 08:35 AM

Hello,
I am in the process of cutting out sections of rust from my floorboard and then MIG welding in patches. I am butt welding them in. I have been grinding down the final weld and so I am left with shiny metal. So what should I do afterwards? I have some spray on primer with zinc in it that I could spray on both sides.

I also have the POR 15 product "Metal Ready" which is labeled as a pre-primer. But I understand this is supposed to etch the metal. It is primarily phosphoric acid and zinc, and the instructions say to rinse thoroughly with water before priming and painting, but I don't want to put water on the inside of my floorboards/interior. I am afraid I won't get all the water out and just cause more rust in other areas in the future.

Thanks!

dvkk · 05-03-2009, 09:34 AM

You can wash it off with a wet cloth. You don't need to pour water in there.

SP2 · 05-03-2009, 11:36 AM

Ok, thanks!

Porsche_monkey · 05-03-2009, 11:40 AM

And dry it with a heat gun.

Zeke · 05-03-2009, 12:43 PM

I don't like Metal Ready. It leaves a goo on the surface if you don't get it really clean. Ospho or The Must For Rust works better. If you have shiny metal for your welds, why not weld it up and prime it? Unless you are treating for other rust, you don't need acid. And, acid left in the pores will rust 10 times as fast.

Classic · 05-03-2009, 01:54 PM

I'm no expert, but i like to dress the weld down and then run some fiberglass based filler over the welds (ever coat all metal) that way i know that i've got a water resistant coverage over any pin holes that may be left in the joint.

I've seen some people use JB weld over their weld joints, for the same reason.

Epoxy is my preference, but a decent etch also works, and then Wurth SKS or spray-able seam sealer to match the original finish.

I like to treat any area prior to welding with Picklex http://www.picklex.com/ although it does not like Etch primer over the top as the acid can't get through the protective coating.

Hope that makes sense, and helps.

Tony

Flieger · Flieger's Garage

Careful welding around zinc/galvanized metal. Fumes are harmful.

SP2 · 05-03-2009, 03:07 PM

Thanks guys. This is answering my question. Flieger, this is a 1969 car so it's not galvanized. I am new to welding, thus the questions. I would prefer not to put anything, but I don't want to find out later that I was supposed to.

Milt, I do have freshly ground shiny metal prior to welding, and I carefully approximate the edges prior to the butt weld. I'll post a pic later, but the welds look good and a contractor who knows how to weld (working on my kitchen) checked the welds and said they look fine. A few of the welds were done after my gas tank ran out and looked a little dark, but I caught that problem early.

After the weld, I grind it flat and the whole thing looks shiny. So I think I might try:

1) Grind flat, then vacuum up debris (inside)
2) Prime with zinc primer
3) Paint black

What do you all think?

Right now, I don't care what the underside of the floorboards look like. I just want no future rust. (Althought I am tempted to steam clean the entire underside and then paint a uniform black before I start installing my suspension.)

Porsche_monkey · 05-03-2009, 04:36 PM

Quote:

Originally Posted by milt

I don't like Metal Ready. It leaves a goo on the surface if you don't get it really clean.

I use it all the time. I apply it, rinse it off, and then dry it right away with a heat gun. I've never seen any goo...

(Milt: Did you see the project Zeke update? I expect you to fly up here for a test drive.)