The idea of taking sandpaper to a car can be terrifying.
Using the wrong paper could result in getting the car repainted, which isn’t cheap.
However, if your car has a dent or paint defect, it’ll need some sanding or refinishing to fix it.
In this article, I will teach you everything I know about using sandpaper for automotive purposes.
I’ll tell you what sandpaper grit to use for car body filler and which grit sandpaper to use for primer before painting.
By the end of this article, you’ll know more than enough about auto body sandpaper to tackle your project with confidence.
Table of Contents
Auto Body Sandpaper Grit Chart
- 40 – 80 Grit: Sanding to bare metal, removing paint & rubbing deep fills
- 120 – 320 Grit: Plastic bumper & fender repairs, shaping filler & glaze/glazing putty.
- 400 – 800 Grit: Sanding primer & sealer (if required)
- 1000+ Grit: Blending and sanding clear coat, removing imperfections & color sanding
The most important rule of auto body sanding is: Always use the least abrasive paper possible to get the job done.
If you don’t use this rule, you will end up damaging materials and creating a lot more work for yourself.
As you become more experienced you’ll know what you can get away with, but until then, it’s best to be on the safe side.
What grit sandpaper should I use to sand a car to bare metal?
The quickest way to sand a car to bare metal is to use P40 sandpaper. The quickest and safest way is using P80 grit. This is because the 80 grit doesn’t damage the substrate.
If you speak to an old-school panel beater or body technician, they’ll probably tell you 40 grit.
Nowadays, IMI, the institute of the motor industry swears by using 80 grit.
If you have a high-quality 80-grit sandpaper from Mirka or 3M it will remove the paint in no time. Unfortunately, if you have a rubbish brand of sandpaper and 80 grit disc will just tickle the panel.
40 grit paper is seen as too harsh of an abrasive. If you see sparks flying when you’re sanding, it’s cutting into the panel and weakening it.
The other problem with 36 or 40 grit discs is the scratches that it leaves behind. It’s very hard to remove these scratches by sanding them out and will almost always require filler or Bondo.
We don’t want to damage the substrate! We’re trying to repair it.
I try to use 80-grit paper as much as possible but there are times when 40-grit makes sense.
40 Grit will sand a car to bare metal quicker while keeping the panel cooler in temperature.
I recommend having both of these grits in your toolbox if you’re doing any type of panel work. There’s definitely a time and a place for both.
What grit sandpaper to use for a plastic bumper?
P180 is the lowest grit that IMI recommends for sanding and shaping plastic. They say any lower damages the substrate, causing deep scratches and thinning material.
I’ve seen people go as low as 40 grit on plastic bumpers, trims, and moldings, but you definitely don’t want to do that. It’s way too harsh and will thin the material a lot.
You can get away with using 40-80 grit to tear down high spots and remove excess material when plastic welding but it’s not recommended.
You’ll generally want to start off using 120-180 grit.
Most of the time I use 120 grit to sand and shape the area local to the repair. This will cut high spots and remove paint quickly. I’d then hit it with a 180 disc to smooth the plastic before the filler work.
If you’re using plastic filler. A lot of them form a hard layer on top of the filler which is time-consuming to sand with 180, in this case, I’ll hit it with a 120 before switching to 180.
Whatever you do, always make sure to finish in at least 180 grit.
If you want to be extra nice to the painter you could always go as high as 240-320, but 180 is the absolute lowest that a plastic repair should be finished with.
What grit sandpaper to use for car body filler?
Sanding body filler can be a long process. It’s common for technicians to use paper anywhere from 40 grit to 400 grit when sanding body filler. The paper that you use will vary based on the stage of repair.
On bigger repairs with deep fills, you will want to sand the first fills with 40-80 grit paper. This will cut down the repair quickly and allow you to get the shape of the panel correct.
As you get closer to the repair being finished. Say it’s 80% there, you should move on to 80-120 grit paper.
Finally, when rubbing your final skim, whether it’s filler or Bondo, you should try and finish with 180 paper.
The type of paper you use will also change based on the type of filler you’re rubbing.
When rubbing fiberglass or aluminum filler you’re going to use a lower grit paper because they’re harder to rub.
Obviously, when rubbing a final skim of glaze, Bondo, or putty, you’re going to use a higher grit sandpaper such as 180 or above for a better finish.
As you become more experienced with body filler, you’ll know exactly what paper to use for each stage. Auto body is a trade that’s all about time & experience.
What grit sandpaper to use to block primer before paint?
Once the repair has been finished and smoothed with 400 grit, it’s then up to the painters to prime & block it.
400 – 600 is generally considered the range of sandpaper used by painters for sanding imperfections and blocking primer.
I’ve seen many painters going up as high as 800 when blocking their finishing primer but this is pretty rare.
Preparing Adjacent Panels For Blending
If you’re painting a new panel and looking to blend adjacent panels you’ll most likely be using 800-1000 Scotch-Brite or sandpaper of 1500+.
What grit sandpaper should I use to sand car clear coat
Anything 1200 and above are used for color sanding, clearcoat and removing imperfections from paint.
Color sanding is a process where you sand the paint with very fine grit sandpaper and then repeat the process again with finer sandpaper. This can be done with sandpaper anywhere between 1500-4000 grit sandpaper.
After sanding you’d then polish the paintwork with very fine rubbing compounds to get the glass-like finish that all painters want to achieve.
Rubbing Compound
While rubbing compound is not a sandpaper, it does remove scratches and imperfections from clear coat on a car. It also smooths the surface and provides an extra level of gloss and shine.
For best results use a dual action polisher to buff the car with a reputable rubbing compound such as meguiars.
Conclusion
Auto body and paint refinishing is a trade that’s based around trying things out and experience. This is why “helpers” & apprentices are so common.
While there are definitely grits of sandpaper that are better for repairing and refinishing cars, it always helps to listen to others and pay attention to new developments in the trade.
As you develop and become more experienced you’ll have your own techniques and methods to tackle dents and perfect your paint.
Don’t be afraid of messing up. It’s all a part of the journey.