undercoat
 

when i got my car, it had a bad axle seal. so one wheel well is full of grease. this made the undercoat in there soft and some of it scraped off. so, i just removed it from that side. i'd like to just respray it with undercoat to match the rest of the car. the rest of the undercoat is fine. but i see a lot of people remove the undercoat on their cars and just paint the underside. Is there a reason for that? I'd rather not remove the undercoat from the other wheel well, but i do want them to match.

The traditional spray can undercoating traps moisture and rotes the metal out. If I ever undercoat mine, I'll use bed liner like Rhino Liner.

If going to bare metal first is an option: POR15 that (super nuke-proof rust seal) then use the Rhino (or 3M, or...) as the actual "undercoat"
The POR will prevent rust, the undercoat will help deaden the sound of gravel rattling around against it...

Stu Aull
80GS
AZ

I used Pitt-Gaurd. It is an direct to metal epoxy mastic and suggested to me by the guy who will be helping me paint my car, who has been in the industry for decades. Anyways Pitt-Gaurd is inexpensive (half the price of POR 15) and Epoxy Mastic is used to paint bridges, oil rigs and ocean vessels as some examples. There are other brands of epoxy mastic, but so far I am just tickled with it. See my build in the link below for pictures.

can you just get a spray can of the Pitt-Guard? I only need to do the one wheel well.

no, it comes in one gallon cans of 2 part epoxy. total of two gallons worth of product. I am assuming you are not looking at redoing the entire car like I did. I would head to a local paint shop and discuss your options there. They may have some aerosols that could help you out.