Any tricks to color-sanding?

[funy1guy]

I just noticed what appears to be a slight orange peel or paint shrinkage (?) on my door panels (they were repainted 6 years ago) and was wondering how difficult color-sanding is. We are a small town and the closest quality Porsche specialist would be Seattle or Portland. Is this somthing I should leave to a pro?? Thanks in advance.

1989 Speedster (black)

[CarreraS2]

If you've not done it before, and it's only one door, and its on an '89 Speedster, I'd probably not try it.

You don't need a "Porsche specialist" to do it. It isn't a porsche specific task. You just need a body shop or experienced detailer. They could get the door done in a half an hour to an hour. Probably cost $100 to $200 depending on your local rates.

If you really want to do it, I'd suggest going with a 2000 grit paper, which is very mild (a pro would likely start with something heavier), use lots of running water, and go easy. Then you use decreasing grit polishers to polish it out. You could use an orbital to polish it, but a pro would use a direct drive high speed buffer to quickly get all the swirls out. You would not be able to do this by hand.

I've done this myself, and I've seen pros do it. A lot of people freak out about color sanding, but I've found that if you use a 2000 grit paper, and go easy, it's hard to do damage. Start with the lowest grit papers and polishes that will do the job and go slowly, and I've found it's not a problem.

But, I cut my teeth on homepainted 914s. I would NOT want my first attempt to be on an '89 Speedster. (Although since the door has already been painted once - and it doesn't sound like it was a great job - the worst that would happen is you ruin it and have to get it repainted again!).

The other issue is if your door has been repainted, but the rest of the paint is original, you don't want to do a "full" mirror finish color sand on the door. The factory paint has some orange peel in it. If the paint on your door is made as smooth as glass, it won't match the rest of the car, which is the goal.

Bottom line, I'd find a very good, high end shop in your area to do this for you.

[scottb]

Originally posted by SoCal911SC
Then you use decreasing grit polishers to polish it out.

I'm not a paint expert by any stretch, but wouldn't you use INcreasing (i.e., finer) grits to polish it?

[DW SD]

probably descreasing in grit size. fine compound is smaller (a decrease)than course.

Doug

[scottb]

That's what I assumed he meant, but to a newbie out buying sandpaper, he might buy smaller number paper, which is coarser.

[Zeke]

Originally posted by scottb
I'm not a paint expert by any stretch, but wouldn't you use INcreasing (i.e., finer) grits to polish it?

Picky, picky.

Color sanding is an art indeed. If you only use 2000, you are likely to do little or no damage, as Brian says, assuming you stay away from any edges. However, you are also not likely to take out the orange peel. To do that, you must have a flexble block and something that will cut quickly skimming off the high spots. I would start with 600 and use it for only a couple of passes.

To examine what you are achieving, use a squeegee to remove the water and see the dull vs. the shiney. Once you see all dull, you are there. In fact, I would be careful approaching that point. Using progressively finer paper (avoiding the words increase and decrease )as you go is the trick, ending up with the 2000.

You must remove all of the sanding scratches from the previous grade of paper with each sanding. So you can see that, overall, you are removing a lot of paint. Be carefull to keep everthing from contamination from dirt and grit or you will make some deep scratches. Absolute cleanliness and copius rinsing with filtered water are recommended. A cotton rag around the hose end is sufficiant and protects the finish from the hose should you accidentally bump it. Some cut off the end.

It has been mentioned by pros that 3 coats of clear are necessary and one will be removed in the process. If you don't know the thickness, you start with an serious disadvantage. If you don't know the paint system, you start with even more of a disadvantage because many single stage metallics simply can't be color sanded sucessfully. I've ruined enough to know what I'm talking about here. And, I've had some great sucesses.

The polishing phase follows the same principles with a couple of different grades of compounds and wheels as well as extreme cleanliness. Don't mix the wheels. You don't want to produce any scratches at this point. Always work toward any edges as in buffing off the edge instead of onto the edge, directionally speaking. Again, the pros use masking tape to protect edges. If you look carefully, there is seldom any orange peel at a crown or near and at an edge. It's a fucntion of the paint.

Experimenting on a junk car is worth the time. If you do the job and it turns out, the satisfaction can't be duplicated. If you mess up, the frustration and anger are overwhelming.

[speeder]

If someone cannot figure out that you want to use finer paper in steps, (not courser), they should definitely not be considering this.

Brian's advice was good, and to reiterate what he said, factory paint jobs of that era had a LOT of orange peel. So much that it amazed me on the showroom floor. Some new owners had their cars color-sanded before they took delivery of them brand new, if they were really picky.

[gr8fl4porsche]

Practice on someone else's car first.

[krauthead]

One thing that might help you. Try using a squeegee of some sort as you are sanding. A small window squeegee(about 4 or 5 inches) works well. You'll be able to see exactly how much of the orange peel you are removing. The idea is to remove as little paint as possible and then buff.

[CarreraCab]

Hey FunnyGuy, Milt has covered it pretty well, the only thing additional that I would advise would be to add a small amount of dishwashing soap to your wet sanding bucket, it will aid you by helping your paper to not load up with paint residue. Also, use a flexible block and only go in one direction (front to back) Good Luck, Doug

[widebody911]

Here's some pix and stuff I have on the subject

http://www.rennlight.com/howto/colorsand/

[Purkinjefibre]

I agree with most of the advice already given. You might need to know if this is a straight colour or not. Some blacks have a clear coat. If it does have a clear coat try not to go through it. If it is straight black, try using 1000 very lightly, then go to 2000 . use lots of water and detergent. use the squeegy as suggested. You can also use a nice chamois leather to wipe the surface dry and clean between rubbings. 600 is a little too coarse in my opinion.
The key thing is to make sure you did not get dust or dirt between the paper and your paint. You will hear it if you do. it will make a small graunching/ squealing sound. If you here that noise STOP and rinse everything. Just try and keep everything as clean as possible.
Then polish and buff using an orbital buffer.
3M is a good source for the things you need.

[Dan in Pasadena]

Some of the best advice sounds like practicing on a junkyard VW fender. I'm going to try it.