factory primer wont come off...

[ratfreak8871]

i'm using a 60 grit flap disc and a synthetic wheel on a 4.5 " grinder and neither will hardly go to bare metal. used them on the back of the cab and either one will go to bare metal fast, but not the top of the cab?????

[Foot Stomper]

Then leave it there. There is no point in removing a "tightly adhered coating".
If you have body work or are going to straight to high build primer, you have a 100% reliable substrate to work with.

Too many times folks get down to bare steel needlessly only to have to deal with flash rusting and the extra work of getting to bare steel for a zero net gain.

[tinydb84]

I agree with Foot Stomper. Unless there is a reason I would just hit it with 80 grit and work from there.

[Keith Seymore]

Originally Posted by ratfreak8871

i'm using a 60 grit flap disc and a synthetic wheel on a 4.5 " grinder and neither will hardly go to bare metal. used them on the back of the cab and either one will go to bare metal fast, but not the top of the cab?????

What model year vehicle?

If the cab was electrostatically dipped (ELPO) then the primer is impregnated into the metal.

K

[ratfreak8871]

Its a 79 c10

[Keith Seymore]

Yah - it's ELPO.

The carrier (and therefore the cab) are electrically charged while the vehicle is in the dip tank. That opens the pores of the metal so that the primer gets right down in the metal. Once the vehicle comes out of the tank the electrical charge is cut off so that the pores of the metal close up around the paint.

The vehicle is immediately rinsed with water and then on to the paint oven for baking.

http://www.73-87.com/7387info/Assembly%20Line.htm (photos 8 and 9 specifically)

K

[ratfreak8871]

Thanks for the replies everyone. Keith thank you, those photos are awesome. I guess I'm good to go. Waiting on fed ex then time to spray