Body panel tar like sealer?

[Torque454]

What is all the black tar like sealer stuff that is between body panel joints and other places? Where can i get some? Anyone know? My truck is a Texas truck and has some rust but it is in unusual places.  One spot is between the two panels that make up the firewall, under the hood behind the engine in that seam. I have a tiny rust hole right there. I'm going to grind the rust out and... do something to fix that (not sure what yet) But ill need some of the sealer stuff to finish the job. I also have some rust inside the cab between the cab floor, and the wall of the cab just beneath the drivers side kick panel. Also an unusual spot in my opinion. I have a spot in the floor to fix also but that shouldn't be too bad and I don't think i need the tar stuff for that.

When these spots are done, is it ok to use cheap-ish cans of spray primer to prime the areas before paint? Or does it need to be some expensive, mix up and spray with a spray gun kind of pain in the butt stuff?

[fitz]

It's called seam sealer. 3M is the brand I use. You can buy it in a tube to use in a calking gun or you can buy it in brush on form. It cost about $35 for a quart of the brush on stuff. Any body supply shop will have it.
If your new to welding like I am, this will hide allot of the sins.
You can see how I brushed it onto all of the seams after doing some rot repair on a Nissan 240. 

[csajerreb]

after using the seam sealer you might want to try spray on bed liner. it blends in and covers allot of imperfections. i used it on my firewall after grinding of all the sealer and gunk. it worked pretty well.

[joesgarage71]

You can get seam sealer in a tube too.