Hard tar like substance.

[Anilyst]

I would search this but I really don't know what it is called maybe you guys can understand me. people use this coating to coat the under body of old cars and I saw at a show some dude coated the who inside bed with this black tar like substance that gets real hard and rough. just trying to find out what this is...

hope you guys understand me lol.

 

[Chewy]

Did you look at Eastwood - Auto Body Repair Tools | MIG Welder | TIG Welder | Plasma Cutter | Auto Body Supplies & Accessories

 

[Cthulhu]

It was typically just called undercoating..
Undercoating | The Auto Protectors | Calgary, Alberta

The stuff inside the bed is bedliner.. Rhino liner is a common one seen around here for most trucks.

 

[fonzyn75]

idk how good it is but walmart sells undercoating in spray paint cans