[Chris J]

I have a friend who has been detailing for years. He kind of got me into it. He works at a body shop as a detailer where after a panel is painted they use a da machine with a special backing plate and a special 3M sand paper to sand out the orange peel and dirt in the paint. He then follows with a finer grade sand paper (3000 grit I think) to make it easier for buffing. He has been complaining latey that after the panels are sanded and buffed out they appear nice for a while but then the sanding patters of the da reappear on the surface and it appears dull again. He even said one of the customer brought a black car back to the shop because they werent happy with the marks. Im helpless when it comes to this since im barely learning how to buff let alone sand anything! Any thoughts on this guys or tips that he might be doing something wrong? Thanks for your input.

[LAbeemer]

when i learned to paint I was told NEVER to use any machine to wet sand. reason you wet sand is to keep the sand paper clean and to lubricate the paper for a finer sand. When the guy at my old shop would wet sand a car he kept constant water running and was very anal about his sand paper. I would have to belive the DA is getting build up too quickly under the paper. Short cuts never turn out as nice and detailed work!!

[Chris J]

Originally Posted by LAbeemer

when i learned to paint I was told NEVER to use any machine to wet sand. reason you wet sand is to keep the sand paper clean and to lubricate the paper for a finer sand. When the guy at my old shop would wet sand a car he kept constant water running and was very anal about his sand paper. I would have to belive the DA is getting build up too quickly under the paper. Short cuts never turn out as nice and detailed work!!

That is very true. however he doesnt have much time to work on each vehicle because they are not details he is doing they are just cars that have been repaired and have a certain deadline that they have to go home by. So what im trying to find out for him is are there any tips on sanding that way that would maybe avoid those track marks? Has anyone ever experienced this?

[FMINUS]

You get a much finer and even result by using a machine than by hand

[Chris J]

Originally Posted by FMINUS

You get a much finer and even result by using a machine than by hand

any tricks on what he should do to not leave such deep trails in the paint after the buffing? 3000 grit for longer time? DA Speed when sanding? Different pattern or technique?

[LAbeemer]

Originally Posted by FMINUS

You get a much finer and even result by using a machine than by hand

Maybe for body work but for wet sanding this is not true at all. The power sander moves to quickly taking off too much material, clogging up the ultra fine grit sandpaper. Hand is gentle and controlled enough. wet sanding is not something most paint jobs need, its for high end paint or for mistakes and or poor painting ability. I know plenty of painters who can paint super nice without a wet sand.

As for your friend keep an eye on the paper keep the hose running slowly over the sanding area and keep checking the paper and changing it as needed. This sounds really poor quality speeding through a process like wet sanding!

[tintivilus]

Pics were recently posted here of a pro detailer in the UK using a pneumatic wetsanding setup, so it's not unheard of.

[haper]

Originally Posted by Chris J

buffed out they appear nice for a while but then the sanding patters of the da reappear on the surface and it appears dull again.

as others mentioned, using a DA to sand is ok as long as you use the proper steps, 1000 grit, 2000 grit, 3000 grit, heavy polish (M109), intermediate polish (SIP / IP) finish polish (106FF / FPII).

b/c you say "they appear nice for a while", how long is a while? there is a chance the polishes he is using are filling in the sanding marks and once the filling capabilities wear away the marring reappears.

[328i]

You can't use a DA like a PC or Megs to color sand, I believe the throw is too large and sanding marks will be too difficult to remove afterwords. There are sanders that could be used, but they require an air compressor and I would not recommend it for amateurs. Also, the fact that you're friend says the cars look dull after a while means they aren't finishing them properly and just using polishes that fill not remove the sanding marks.

[LAbeemer]

I will agree that untrained detailers should not use a regular DA sander to color/wet sand a car. There are newer better equipment on the market for high volume detailers to speed things up. But like anything else the room for error is greater. Hand sanding for color/wet sanding is the best IMO because there is less room for error and it give the best attention to detail. I also agree with that assessment, if it becomes dull over time its because the sanding wasnt done right and was just covered up with wax and sealer so when it wore off the lousy sanding job showed up again.

[Chris J]

Thank you everyone for your help. I will let him know. I think his body shop just needs to buy him the right equipment to do the job and stop being so cheap.