Seems like this is an area where people go firmly in one direction or the other, and I'd like to hear arguments for or against either way. So, which do you prefer and why?

Thanks graemlins/thumbsup.gif

Do what I call a X hatch and then change directions. I think it is the best way to get it straight. Wet or dry, depends on how close you are to finish primer. If you are close to finish primer wet sand.

What Redman said. Initial primer sanding is dry with a long board. When the major peaks and valleys are gone, then it's wet with shorter blocks/pads. The final sandings are ALWAYS wet, but that's just me.

The basic rule for blocking is the X hatch pattern as mentioned above. On larger areas I tend to use a 6 point star sanding pattern. Also one common mistake it to apply pressure to that sanding pad. At this point in finishing the primer, only the weight of your hand and the pad should be used. No pressure or force should be used because you are just knocking off the top of the primer and bringing it smooth and level.

Wet or Dry depends on the painter and products used. Consult your painter about his preferences AND the paint product info. A lot of shops around here don't wet sand primer anymore. It's a matter of time because wet sanding takes more time and in a production shop time is $$$. Some have the opinion that by wet sanding the primer the paint will lay out better (flatter) on the surface which will result in a more even/balanced finish. I can see this being the case with high metalics, candies or colour shifting paints.

Wet Sand:
If you want to wet sand the primer than don't go any finer than 400 wet and I would VERY HIGHLY RECOMEND that you use 3M Imperial Black Wet or Dry 400 paper. This will give you the equivalent of 600 dry and will be very very smooth. Any finer than this and you may experience adhesion problems down the road.

Dry Sand:
Most shops prefer a good dry sand to 400 and then paint on top of that. It makes for good adhesion because there is plenty of bite for the paint but not too much to be visible or cause streaking or sanding marks. For this I would recomend using 3M Imperial Gold 400 paper.

The bottom line, it depends on the painter & the product requirements for the paint. Wet sanding really comes into play when doing finishing on the clear coat. If you want that mirror finish show shine, without any imperfections in the top coat then that's the time to wet sand and finish buff. If you are sanding the paint because there are lines painted on or something else prior to the clear coat, then wet sanding is the only option.

Hope it helped.

I wet sand while doing the car to keep my paper clean and the dust down. Then I just hose the whole stall out.

with the finer grits wetsanding is definately faster, the abrasive action is unarguably more aggresive, just look at most paint manufacturer's recomendations on final grit before paint application. Most will say 400-500 dry or 600 wet. Dry sanding is not faster, and is less aggresive.

Sometime back I started to keep a log on the time spent sanding parts. I found that dry sanding was faster and way easier to clean up and get it ready for masking/paint then wetsanding.

I too have noticed that many shops have switched to nothing but dry sanding even when buffing out clear. Once you are done with the sanding dry method saves time in the paint prep department, no chasing water around with the blow gun, no worries of trapped water coming out at a later time.

I never had a problem with the method and paint I use which is PPG, others will be different. I dry sand with 320-400 depending on what it is. Then seal the area that recieved the 320-400 sanding. All other areas are sanded dry with a da using 800 grit.

To me dry is faster. If you brush off the surface and block every so often you dont get clogs and the paper stays fresh.

Its one of thoses deals that you need try for yourself, each person will react to same action differently. But hey thats me, some prefer a big block others prefer a small block, I like Buicks smile.gif . Nothing but what you know and like...Eric

I have to agree that for a production shop wetsanding can be a PITA, trying to dry the car prior to paint application right after wetsanding is definately a challenge. I do agree most production shops drysand for this reason and also so they don't have to deal with cleaning the sanding sludge from the car and floor. As an insurance estimator/inspector I visit 47 shops on our program and almost the same number of non program shops on a regular basis. Most of the higher production shops do not wetsand other than denibbing and colorsanding of the paint. In fact most of these shops do almost no final blocking at all, DA sanders do the finishing work and from what I see quality suffers. So yes, in a production type atmosphere where in and out is the name of the game, drysanding will speed the total repair process. But IMO, if you can wait for the water to dry before paint is applied wetsanding with a block is the best way to go. I've done it both ways, drysanding with a block- brushing the block or blowing it off with compressed air as I go trying to keep the grit clean and feel that wetsanding is easier and ultimately faster. I also use about 50% less paper wetsanding. To each his own I guess. It can be done either way.

Originally posted by baddbob71:
In fact most of these shops do almost no final blocking at all, DA sanders do the finishing work and from what I see quality suffers. Thats what happens in the shop i work at.I block,prime and reblock to perfection, only to have the painter hog it down with his DA. Sometimes i wonder why i bother. graemlins/sad.gif

I guess I misread the original post. My personal preference is to finish the primer with 500 wet prior to paint. I have never had a problem with that but it is a bit more time consuming and there is the inevitable sludge that needs to be cleaned up prior to paint.

I do believe that the better the base the better the finish. Clear coat has a way of magnifying everything beneath it and in some cases it REALLY magnifies stuff.

It is amazing what some of the stuff looks like coming out of some shops and boy can you ever tell that they were rushing and took short cuts. Even some of stuff off the assembly line looks pretty awful and yet people accept it. If I was to drop 30K on a new ride, you bet that I would want it to look near perfect, not like a pretty coloured orange.

Steve

Originally posted by 70isfine:
</font><blockquote>quote:</font><hr />Originally posted by baddbob71:
In fact most of these shops do almost no final blocking at all, DA sanders do the finishing work and from what I see quality suffers. Thats what happens in the shop i work at.I block,prime and reblock to perfection, only to have the painter hog it down with his DA. Sometimes i wonder why i bother. graemlins/sad.gif </font>[/QUOTE]Thats something I just dont get :( Now yes am guilty of running a da over it a time or two but quickly learned it looks like sh!t.

When I dry sand I use nothing but regular ole long blocks and the 5/9in rubber blocks with 3M Gold roll paper. I achieve the same results that I get by wetsanding. But once again thats me.
Theres nothing wrong with either method

Hmmm.... I was just talking to a guy that I was considering to use to lay the paint on, and I asked him about how he would like it when it gets to him as far as finish sanding the primer. He said that I could block it with 320 and then he would go over it with 500 on a soft backed DA. Now that didn't seem like a good idea in my mind, and after reading all your replies (as far as DA use) I think I'm going to keep looking for another painter.