I have been wondering for the longest time about this. Is this some kind of coating or is it part of the steel unibody? I notice it's on the rear bottom edges of the front right and left fenders also.

Thanx.

I believe it's a coating to prevent the body from rusting.

Yes, it is a coating, but it's not black in color. More like a silver if I remember correctly. How do I know this? One time I was driving down the road and a kid was sitting on the side of the road throwing rocks at cars as they were driving by. He hit me. Fortunately, he hit me down low, right in the rough area. I was able to put some undercoating on it, then touch up the area and it appears to be holding fine.

I went and talked to his mom and apparently, this is not the first time this has happened! Needless to say, I still drive this route all the time, and I haven't seen him there since. If he had hit my car anywhere else, I would have systematically killed their entire family.

It also serves as a sound deadening material.

i also wanted to know why the underside of the sideskirts is bumpy? I feel down there and its not smooth like the body but painted like thebody but is rough.

Does anyone know if you had to replace a fender would the OEM fender replacement have it on there or would a bodyshop have to add it?

IF you are talking about the bumpy coating at the near the bottom on the sides of the car, it's there to protect you from getting chips from stones/rocks. The coating is like the texture on a golfball.

http://www.grafx.dk/pages/tutorial/finished.jpg