Go over factory undercoating?
 

I want to clean up the underbody of my 68 912. I just want it to be clean and black. Do I need to fully strip off all the old stuff or can I clean it and go over it with something? It would be easier to brush than spray

http://forums.pelicanparts.com/uploa...1353740635.jpg

As long as it is clean and oil free. I use dawn dish soap then hose it off. You can just use spray undercoat.
Make sure you check the corners for cracks and loose factory undercoat.

dish soaps do work well for cleaning but make sure it's a product with out any lanolin in it . your best bet would be to use a pre paint cleaner .
then sand the chassis with a red pad and clean it again with paint cleaner .
i would not use a rubberized under coating it will not have the look you want and it's a crap product .
i would opt for a product like transtar's black chip guard in a spray can . 2 or 3 cans will do the under side of your car .
spray chip guards don't have the over spray like paints do so you don't have to go to nuts masking off the car . just lay some old sheets over your 4 post lift and on the floor right under the car . thats if your floor is paints or coated and nice looking and you want to keep it that way .

Good tips. Thanks guys