What do you need?
At the minimum, you'll need
- masking tape
- an assortment of sandpaper (400-1000 grit)
- a bucket of clean water, and some microfiber towels
- You'll also need to purchase or rent an electric sander if the car isn't small enough for hand-sanding.
The first thing you want to do is tape off your car. Masking tape works well, but it's not recommended for the paint itself as it can pull up some of the paint.
This isn't a huge deal if you have wax undercoating or clear coat because it will just give your paint that much more depth and shine.
Make sure all of the windows are masked off so no water gets in them! If any are open, close them so they don't have to be taped shut later. You'll also need to mask off rubber trim pieces to protect them from being eaten away by the sandpaper grit.
Health and Safety
As always, safety first! Make sure your sander (or yourself) has a dust mask and safety glasses.
Wear shoes that cover your entire foot, pants that cover your shins, long sleeves or a full-length shirt, and gloves . You'll also want to wear face protection.
If you're working on wheels/tires, put the car in neutral so it doesn't roll away with the parking brake engaged. Put chocks under each tire for extra stability.
Now turn on your sander and gently touch the spinning pad to the paint surface. If it clicks against the car or makes a squeaking noise as it tries to stop spinning, adjust your pressure until it glides smoothly over the paint surface.
As a general rule of thumb, start with the lowest grit sandpaper you have, no matter what grit you intend to finish with.
The last thing you want is to have deep scratches from the wrong grit of sandpaper because it's too difficult to fix them properly. Sanding by hand is completely fine for this part so don't let anyone tell you otherwise!
Sanding the Car
1. Now that your sander can glide smoothly over the paint surface, start sanding, starting at the top of the car and working down.
2. Divide up your body panels into sections that are about an arm's length wide then work on one section at a time until it's done before moving onto another area.
3. Work slowly with light pressure - sander burn through paint very quickly even if set on low!
4. For areas where corrosion has started, you may want to go over it twice with the coarsest grit sandpaper you have; if there's any scratches that still remain after that then move up a bit and work on those areas again.
The next step is to clean the car.
If you've had any undercoating or sealant that was applied at the factory, it may be best to strip it off because that will have protected the car from corrosion up until now. Either way, use a clay bar on top of your sander's dust mask so you don't fill your lungs with iron particles!
Work slowly in one section at a time and make sure you cover every area - even if there are no visible scratches or defects you'll want to make sure there aren't any microscopic ones either. The claying process should only take around 15 minutes per panel, depending on how dirty the vehicle is.
Afterward start washing out all of that loose dirt and debris with a pressure washer/bucket of water on the highest setting. .
Washing and Aftercare
Now that everything's been washed off, wipe down each panel with wax and grease remover. Once again, avoid breathing in any chemicals by using your dust mask.
Take some time to get into every nook and cranny - if you don't remove all wax/grease remover from anywhere on the car it could bubble up under the next coat of wax or sealant, ruining everything!
Before going over to the polisher, wipe the car down again with a lint-free microfiber cloth.
Is it better to wet or dry sand a car?
Wet sanding has the advantage of not having to worry about scratching up your paint, but it can take longer. Dry sanding is faster - even with a sander - but you have to be careful not to scratch the surface.
How long does it take to wet sand a car?
Wet sanding can take hours, and depending on the size and number of panels it could be a full-day project. It's best to leave it overnight.
How long after painting can you wet sand a car?
There's no hard-and-fast rule about how long to wait before wet sanding, but you'll need at least a few hours after you apply the paint. It depends on whether it has fully dried out and cured - usually 24 hours is a good window where it won't have changed noticeably from when you applied it.