How Often Can You Machine Polish a Car?


Using a machine polisher is a great way to remove clear coat scratches and swirls to give your car that mirror finish. But there are definitely risks to polishing and compounding, and there is only a certain amount of times you can do it safely.

In this article, I’ll be talking about why you should only polish your car when necessary, why it shouldn’t be part of a routine, and how many times you can do it. So let’s get started.

The Quick Answer

You should only ever machine polish a car when necessary to avoid removing an excess of clear coat. You can use a paint depth gauge to determine how thick the paint is, and if it’s safe to polish it. It’s normally safe to use a machine polish on a brand new car 1-2 times before running into issues.

What Does a Machine Polisher Do?

It’s really important to know what a machine polisher actually does before moving on to how often it can be done safely.

Machine polishing, and hand polishing for that matter, has one action. It removes paint, also known as “cutting”. The purpose, is to remove clear coat scratches.

The aim is to make the surface flat so light reflects off it evenly creating a shiny and glossy appearance.

Polishing will not remove scratches deeper than the clear coat. So if the scratch looks grey or white in normal lighting, polishing won’t work.

Clear coat scratches aren’t visible in low-level lighting, but they do make the car look duller and flatter overall. However, they can be seen in direct sunlight and often look like swirls or spider webs.

Clear coat scratches that can be removed using a machine polisher

Polishing vs Compounding

It’s also important to distinguish between polishing and compounding. These are the two types of paint correction that can be performed using a machine polisher.

  • Compounding cuts the paint quickly
  • Polishing cuts the paint slowly

Compounding is used to correct deeper clear coat scratches, whilst polishing is used to refine the finish. Compounding can leave some “hazing” behind, because it’s more aggressive. Polishing is performed afterwards to flatten this hazing to create a mirror finish.

Compounding should only ever be used to remove more severe clear coat damage, such as marring or deeper scratches. Polishing is milder, but capable of removing lighter swirl marks.

Risks of Paint Correction

Okay, so now we’ve been through the fundamentals, we need to talk about the risks of correcting the paint using a machine polisher.

Your car only has so much clear coat. If you keep removing it by polishing, then you won’t have any left.

It’s really important to preserve the clear coat because it protects the base coat (colour), underneath it. It protects it from UV rays, corrosion and contamination, all of which would cause the colour to fade and crack.

If you want the finish to look shiny and have that depth of colour, you need to preserve the clear coat.

It’s also worth noting that the risks of burning through the clear coat are much higher if you use a rotary rather than a DA polisher. Take a look at this article I’ve written on DA vs Rotary Polishers to learn more about this topic.

How Many Times is Safe?

So how many times can you actually polish a car before you run out of clear coat?

Here are a few facts.

  • A brand new car has around 30-50 microns of clear coat.
  • Compounding the paint using a machine polisher removes around 5-10 microns of clear coat when trying to remove moderate clear coat scratches.

So by this school of thought, you’d be able to machine polish a car around 3 times before you ran out of clear coat.

However, you never want to even get close to this situation.

Partly, because it’s difficult to tell how much clear coat your car has, unless you have the proper equipment (more on that later).

But also because the less clear coat the car has, the less protected the base coat is.

A lot of the UV inhibitors in the clear coat sit at the top. So the very top layers are actually the most important. So if you remove the top layers, but still have a decent chunk of clear coat left, you can still have some issues.

You really don’t want to remove any more than 20% of clear coat on your car, based on the amount it had when it was brand new.

That means you really should only ever properly machine polish your car once.

Now this refers to compounding. It is safer to polish your car more often than this. This is because polishes are much milder and remove far less clear coat. However, you still don’t want to make polishing a routine, because if done often enough, will still cause issues.

How to Tell When It Is Safe to Polish

You can use what’s called a paint depth gauge to tell when it’s safe to use a machine polisher. Here’s how it works.

  • Use the paint depth gauge on the door jamb paint to see how thick it is. This will be used as the reference because it usually hasn’t been polished.
  • Use the gauge on a panel to get a reading.
  • Subtract the panel reading from the door jamb reading.
  • This tells you how much paint has already been removed.

Most new cars give a reading of around 120-150 microns. This includes all the layers, not just the clear coat. You don’t really want to go below 100 microns to be on the safer side.

Using a paint depth gauge isn’t a guarantee that it’s safe to polish, but it does give a useful guideline.

When Should Machine Polish?

You should only ever polish or compound your car when you really have to. If you want to remove clear coat damage perhaps inflicted by a previous owner, then as long as the car hasn’t been compounded or polished before, then it should be fine.

But you don’t want to keep doing it. Once you’ve used a machine polisher on the vehicle, you should be really careful not to inflict any more clear coat damage.

As a general rule, light machine polishing a car should not be done more often than once a year, and only after claying the car. However, you should not machine polish a car as part of a routine and should use a paint depth gauge to determine if it is safe to machine polish.

Are There Any Alternatives?

Okay then, what do you do if your car has clear coat scratches and swirls, but it’s no longer safe to do? Well your best bet in this situation, is to use a glaze. They cover up scratches and swirls using fillers, to hide the scratch rather than remove it.

They are a temporary, but non-aggressive fix. You can check out this article I’ve written about glazes vs polishes to learn more about the differences.

Thanks for reading! I hope you’ve found this article helpful. Don’t forget to check out the rest of the website to learn more about making your car look its best.

Heather

I first became interested in car detailing around 3 years ago and learnt all the main techniques on my very first car. I spend a lot of time detailing my current car, and trying to keep my family's cars looking presentable too!

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