How to choose the right sandpaper grit for car paint repairs

While nobody wants to have to use sandpaper on their pride and joy, scratches and scuffs are part of the risk of owning a car.

If the damage is light and there’s no rust near it, you may be able to repair it using a good quality scratch and scuff remover. 

Or for fine scratches and chips, then a car paint touch up pen could be the answer, offering a precise, colour matched solution for lesser damage.

But for more serious problems, especially if the base layer is showing through the car paint, you’ll probably need to use sandpaper at some stage.

Selecting the right grade to apply is an important consideration, as you’ll want to use the most effective type depending on the job.

And of course, the last thing you’ll want to do is make the problem worse, so these tips should help, along with selecting the right sandpaper.

We recommend Primer Preparation, Topcoat Preparation and Polishing Preparation sanding sheet packs - better value than buying individual grades.

What kind of sandpaper grit do I need?

Grit is a way of classifying sandpaper types by how coarse they are, based on the approximate number of abrasive particles per square inch.

So 400 grit paper has fewer particles than 800 grit - because they’re larger and therefore more abrasive.

Manufacturers will also use the classification system ‘Grade P100’ etc, to mean the same thing.

The larger the number, the finer the particle size and the smoother the resulting finish after use.

And picking the right one depends on how deep the damage is - most cars will have several layers on their bodywork.

The top coat is typically clear, with the base colour underneath and a primer layer underneath that, on top of the car panel itself.

The clear coat, for example, shouldn’t be tackled with anything rougher than grade P1000 sandpaper, unless you want more scratches than you started with.

Usually, as a rule of thumb, the deeper and more serious the damage, the lower the grit number you can get away with.

Less than P120 grit sandpaper 

Usually starting with 40 grit, use this rougher type of sandpaper to fully clear an area of rust or deep scratches before filling and applying primer.

It can even be used to prepare bodywork itself, prior to filler being added and shaped when dry (80 grit is best for this at first).

These coarser papers will leave scratch marks themselves that will need smoothing down in turn.

P120 - P180 grit sandpaper 

These grades can be used to feather edges of filler or remove lighter rust and can also remove smaller scratches.

If spot putty has been used at all, P180 grade can also be used to sand this down.

P320 - P400 grit sandpaper 

These grades are the last to use before primer is added, to ensure the surface is as flat as possible before application.

A very basic tip - if you think you’ve spent long enough and it’s as smooth as it can be - spend longer.

Every extra minute you take care with on this stage, however tedious it may seem, will be reflected in the final finish.

P600 – P800 grit sandpaper 

Prior to applying a base coat of paint, use these levels of grit to remove any final imperfections in the primer.

P1000 – P1200 grit sandpaper 

Finer grades above 1000 grit are used to eliminate any imperfections in the base coat, ideally using a ‘wet sanding’ technique (see below).

P1500 - over P3000 grit sandpaper 

For fine detail finishing, the highest grade sandpaper is used to remove the almost imperceptible marks caused by P1200 before the clear coat is added.

Again, for best results, use wet sanding if possible when working with this level of grit.

What is wet sanding?

Simply soak the sandpaper in cold water for several minutes before use and apply water to the paint surface too.

The liquid reduces friction and abrasion, which aids a smoother finish and also helps prevent clogging.

Wrap the paper round a sanding block for more even pressure distribution and remember to spray the surface regularly.