What causes this defect?

2x1's make great sanding blocks... we were doing a 54 Chevy quarter with one using two people.... no better way to block the entire quarter at once

 

I used to work in a body shop as a paint apprentice, I've seen this before lol

 

In some cases you can wet sand with a little bit 2000 grit and then buff that area and it will make it look a lot better if not completely gone.

 

primer can look fine going into the paint booth and then shrink after painting, no? the body man and prep guys dont have to be idiots because of that spot.

 

That wont do much as the problem isn't with the clearcoat itself. The basecoat and the clearcoat have sunk in to the deep sand scratches.

It is possible that the primer looks fine originally, but then that all comes back to the prep guy. It isn't much so the body man since as a painter/preper, you would expect them to use a coarse sandpaper. The sand scratches should have been feathered out better. If that scratches were that noticeable before, I would have put on a nother thin coat of body filler, just to make sure something like this doesn't happen.

 

I totaly understand and agree with that. I just happen to work in a body shop and know first hand that in some cases a little sanding and buffing will make it look better.

 

That is true, I have seen that happen a few times, but it could of been avoided if they just took a little more time with preping like said before with a thin coat of putty. In defense of the body shop, some times a car has to go so you don't always get to do a super perfect job. Plus the auto body industry is always getting beaten up by these insurnace companies. They will tell you how to fix it the right way but when it comes to actually fixing the car they want you to fix it the cheapest way possible. Si now the guy fixing the car has to work twice as hard to make a buck where before it was a little easier.
sorry, I can rant about this all night

 

Yeah, I agree with you, wetsanding/buffing might help it a little bit, but there is no way it can remove the defect 100%.

Most of the time, sanding/buffing wont do much in these cases as there is nothign to work with since the scratches are right on the surface, so everything is sunk into it.