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Should I Sand Between Touch Up Paint Coats?

Painting a car is a lot harder than it looks. It's by no means the same as spray painting a wall. On a car, if you get just one coat or layer of paint wrong, then you'll have to start all over from scratch. This is an art, which can take a lot of patience and precision to master. But amidst all this talk of paint, one particular subject often comes to mind.

Does one sand between the coats? There are, after all, many individual layers sprayed on top of one another on your car's bodywork. These layers are what gives your car its unique tinge of colour, as well as its richness and depth. So, does sanding it down ruin or improve your car's overall finish, especially with a paint touch-up? Well, the answer is a bit complicated.

In A Nutshell...

You're not recommended to sand after every primer coats, or following the upper base- and clear coats. The justification for this is quite simple, in that the paint might still be a bit too soft or wet, despite it not appearing so to the naked eye, or to the touch. Even just a tiny swipe of your sandpaper could ruin the finish, and you'll then have to sand it all the way down and start over.

You may be (very) careful in sanding it if there is a speck of dust, sand, or debris that lands on the wet paint, and you need to wipe it off. Alternatively, the paint isn't even, there is some paint running blobs down the side, or if the texture isn't right. This too could be rectified with a bit of careful and slow sanding. But otherwise, it's pointless. 

More to that, it makes your paint touch-up job a lot more complex, time-consuming, and expensive for no reason whatsoever. However, there's a lot more truth in the pudding than it might seem. To look at this more closely, we'll look at whether sanding is something you should consider doing at all for every coat level...

1. Primer

The primer is the base of your paintwork, sitting between the bare metal or plastic body underneath, and the colourful paints up top. Using a primer enables greater adhesion, and enabling the paint to stick onto the bodywork a lot better. It fills in any gaps or defects in the bodywork by smoothening it out, as well as providing extra protection for the body from corrosion, UV light, and so on.

One key subject with the primer is that it needs to be smooth and even, thus ensuring that your base- and clear coats are perfect and levelled. Thus, some people have wondered if sanding after every single coat of primer - and the entire primer layer has multiple coats - could help with this. The answer, is no. There's no point at all for sanding after each coat.

The only result that you'll achieve is prolonging your repainting or touch-up process. However, many professional painters do recommend sanding after all the coats of primer are done. Only after the primer as a whole has dried through its many coats, you could sand it to further ensure that the surface is completely smooth and free of debris. This would be immensely helpful later on.

2. Base Coat

Following the primer, you have the base coat. This is where the actual paint comes in, and it's from this base coat that your car gets its colours and dazzle. Just like the primer, the base coat is not applied as a single coat, and is indeed sprayed as multiple individual coats. In this case, sanding between every single coat of the base coat layer, or even once it's done is unnecessary.

As we mentioned earlier, any use of sanding along the base coat should only be done in the case of there being any damage, debris, or imperfections in the paint. With some types or shades of paints, such as metallic or pearlescent colours, sanding could massively ruin the looks of the metallic flakes or pearls. At which point, you'll have to undo that whole coat.

3. Clear Coat

Up top, we have the clear coat. This is a transparent layer of paint that acts as a finisher on top of your base coat and form a protective layer. Although the clear coat is quite thin, you'd still need to - generally speaking - at least apply several coats to form the entire clear coat layer. Just like with the base coat, sanding between coats of the clear coat is not recommended.

If there is some imperfection or defects, then sand it down very, very carefully. This is owing to how thin the clear coat is. If you've sanded past this and onto the base coat layer below, then you'll have to sand away all of the clear coat and repaint a bit of the base coat. Once again, the consequence of sanding could result in you having to spend more time, energy, and money than is required.

Nevertheless, many people recommend wet sanding and polishing only after the clear coat as a whole is done, and fully dried out. A lot of water sits between the clear coat and the abrasive sanding material, which helps to sand down the paint, or any tiny imperfections more thoroughly. The use of wet sanding and polishing compounds is quite popular in the automotive detailing industry.

Conclusion

There is a very familiar pattern emerging here. Sanding is a process that you should use sparsely, and only when there is a need for it. Sanding after the primer layer is complete is a great way to iron out any tiny flaws that you might've missed. The base coat and its many layers can be sanded, but very carefully so, and only when you need to rectify errors in the paint job.

Even then, you should reapply that entire layer of the base coat once more to maintain the look of the paintwork. The clear coat, meanwhile, should be treated the same way. Once that's dried out and complete, a bit of wet sanding and polishing would do wonders at perfecting your car's fresh coat of paint that bit better.