Alright guys - so probably the #1 question I get here and at Autopia is "how do I repair a rock chip or deep scratch", well here is how I do it. Remember, everything in this post is my opinion only. There ARE other ways to do this and lots of different products you can use. Also, remember that trying this is at your own risk. Damaging a paint via PC is hard, but with sandpaper it's very easy. So let's start:
What you'll need:
1) Matched paint. A jar is best, a pen is ok. You can get it at a dealer or local automotive store.
2) A fine paint brush (medium bristles, fine tip), and/or a plastic toothpick.
3) Rubbing alcohol, some automotive wash soap, access to water.
4) Some sandpaper. I like Meg's unigrit 2000 and 3000. Non-unigrit and less than 2k at your own risk.
5) A sanding block. Both soft and hard work. I prefer soft as it is easier to manipulate and can go around curves.
6) Polishes. What kind of polishes will depend on if you're using a PC or not. I will be using a PC, but will include by-hand instructions.
First make sure the car has been washed, what wash you use is up to you. How you wash it is also up to you but remember, two buckets and a quality mitt (or 3).
Second, make sure the area you're repairing is clean. By clean I mean no sealants, waxes, nothing. To do this you'll need to a) use a cleaner polish or b) (my choice), wipe with ISA:water. What's that? It's rubbing alcohol (the regular 70% kind) mixed 50:50 in a spray bottle with water. Spray the area thoroughly and wipe. Do this twice. You want *no* dirt, wax, anything in the chip.
Alright, so filling in the chip/scratch. Two ways to do this, first I will go with my choice for chips and that's using a plastic toothpick. Before I go on, there are good instructions on how to do this here: http://autopia-carcare.com/inf-paint-polish-clinic.html
. I basically follow the same process. Dip the toothpick into the paint about half way up, then touch the tip of the pick to the center of the chip and capillary action will pull the paint into the chip. It will take a couple passes to level it out so let the paint dry at least 4 hours in between and be patient.
The other way is good too, but less accurate. It's good for scratches that are larger than chips and would take too long to fill in via the toothpick method. Put a little paint on to your brush (very little, immerse maybe 1/4 of the brushes tip), and touch the tip to the center of the scratch. You'll see the paint pull into the scratch. Depending on the size begin to move the brush in one direction through the scratch. Repeat this every 4 hours until you're level.
Whether or not you add a layer of clear is up to you. I normally do as I find it makes the paint match better after sanding/polishing.
Alright, so now you have a blob, sort of like this:
Or in the case of a scratch, like this:
No go have a beer and wait until tomorrow (or better yet, two days from now, then come back). This is important - let the paint dry or odds are you'll pop the chip right out when sanding.
The night before you said put the sandpaper in some water and let is soak overnight.
Alright so sanding time. This is the tricky part so go slow and be patient. Make sure the paper is tight on the block (you'll probably have to cut it) and then spray the blob with a mixture of water and some soap (just mix some in a spray bottle), spray liberally and then start sanding. I like to sand against the blob, so figure out which way the blob is longer and sand the opposite way. Sand very lightly, apply almost no pressure and try to keep the block flat. Also, sand in one direction, not back and forth. It's counter-intuitive but it helps. So swipe one way, lift, then repeat. Check your work often by wiping away with a mf towel. Before you do spray the area liberally again with the soapy water to lift up any particulates. You're done when the blob is level with the paint (as in, you can not feel it by running your finger over it gently). You'll have something that looks like this:
And you'll probably crap yourself, but you're ok. As long as you were patient and sanded lightly you will not have removed more than a fraction of your clear. For example, in the second pic above someone might say "holy smokes, you're down to the metal!", but I'm not. As a matter of fact I took a paint reading before and after and I was down less than 0.02 microns. That's under 2% of my total clear thickness. Just be careful!
Now clean the area with your ISA:water and get ready to polish.
If you're polishing by hand I hope you used uni-grit and 2500+ paper, because otherwise you're going to be really sweaty when this is over. Assuming you did go ahead and grab your polish of choice. Products I like by hand are:
Menzerna Intensive Polish
I'd start with something like Sonus SFX-2 or PB's 2.5 on a cotton applicator. Apply a dab about the size of a quarter then start to rub. You *will* need to apply pressure and move quickly. You're trying to generate heat. Repeat until the marring is gone, or 90% gone then use ScratchX to clean it up. You should have nice smooth paint, and the chip should be 100% gone.
By PC I like the same products (minus the ScratchX), or if you're in a hurry SFX-1, Menzerna PG, or PB's SSR3. I usually use SFX-2 via an orange LC pad (medium abrasive), and just polish as normal. Apply a couple dabs to the pad, work in at speed 3 for 20-30 seconds and apply enough pressure than the PC almost bogs down, then kick it to 6 and apply the same pressure until the polish flashes. One or two passes will take out 2500-3000 grit marks easily.
Now, if you have some marring that isn't coming out you can do one of two things. One, use a stronger combo of pad+polish, or two, sand again with a higher grit then polish. I like option 2 because it's quicker and works better, but if you're nervous about that try option 1 first.
When you're done clean again with isa:water then apply the wax/sealant on your choice and call it a day. Here are the afters of the chips/scratches I posted above.
The blob was in the circle.
Scratch was in the circle.
Questions, comments? You know where to find me. Some pics for your enjoyment!