I have been working on a car project lately and I had to do a little body work so before I get into the whole project I wanted to give you some help picking the sandpaper you will need for shaping bondo and sanding paint.
The first rule of auto body is that you always pick the least aggressive sandpaper that you can.
This is because while repairing the area you don’t want to cause damage in the way of deep scratches that will just require more work.
Auto body sandpaper comes in standard numeric grades from 36 grit which is the most aggressive to 2000 grit which is so smooth you might think they sold you a regular piece of paper and told you it was sandpaper.
Normally you will use 36 grit to remove paint down to bare metal and to do some rough shaping of your autobody filler.
Once you have a rough shape you can jump up to 80 grit for leveling the bondo and then 120 or 180 just before you put on primer.
For painted surfaces that just need to be cleaned up you can remove chips with 220 grit wet sand paper and then apply primer.
Once you have primer on the car you can sand with a 400 to 600 grit sandpaper just before you apply paint. Use the 400 grit paper to block sand and remove any primer runs then 600 grit to provide a good surface for the paint.
After painting your vehicle you can use 1000 grit sandpaper and wetsand out dirt then 1200 grit can be used on the entire surface before buffing.
Now here is a good tip that you need to learn
No matter what product you are sanding whether it be paint, body filler or fiberglass if the sandpaper starts to clog covering the surface in just a minute or so you should try going to the next aggressive sandpaper.
Today I was sanding some fiberglass filler which is like standard bondo filler but has a fiberglass fiber and gel in it.
For the past few days I found that 80 grit was working really well to cut down the filler after it cured but either I did not add the same amount of hardener.. think I was adding a bit too much yesterday.. or the filler cured slightly different.
I first tried using another piece of 80 grit. The piece I was using came off my DA Sander and might have been worn a bit. This clogged up too.
I then grabbed the pack of sheet sandpaper I must have had around for 15 years and pulled out a piece of what I guess was around 40 grit paper. This took the top layer of gel off the filler and sanded down to a nice hard surface in just a few seconds.
This also happens when you wetsand paint that is garbage.. synthetic enamel or garbage acrylic enamel that did not have a hardener. You will find your paper gums up very fast even if you are wetsanding.. the only thing you can do is jump to a more aggressive sandpaper and remove the garbage paint all together.
When you do this its best to test an area and jump in steps if you have the paper .. don’t just grab 36 grit because your 220 is clogging on you … go to a 180 and that should work.