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What is paint thickness

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Paint is a layer of coating applied to a surface in order to protect it from the elements, or for cosmetic reasons. Although the type of paint can be different, the layer of paint will still have a certain paint thickness.

What is paint thickness

A typical layer of paint, showing how porous the material really is.
A typical layer of paint, showing how porous the material really is.

When paint is applied, it is sprayed on top of the surface it need to cover. This creates a layer of paint that slowly hardens. When it is fully cured, the paint can protect the surface underneath or can serve its cosmetic reasons. There are several reasons why this layer can’t have an unlimited thickness.
for economic reasons, a manufacturer doesn’t want to apply more then is needed. The layer such be thick enough to protect, but thin enough to be cheap. For hinges and other moving parts, the thickness of the paint can become a problem when it is to thick. There is also the weight factor, an average paintjob weighs about 2.7 kg (6 lbs) and 6.8 kg (15 lbs) (not counting custom paint jobs). Although this is not a lot of weight, there is no logical need to add more then is needed. In the world of race cars, every pounds counts, and the paint is applied in thin layers.

Paint is applied on top of a primer, this means that the primer already has a certain thickness. Then the primer is either covered with a colored coat, or a unicoat of paint. The colored coat is then also covered in a clear coat. (the unicoat isn’t covered with clear coat) This all adds up to a certain thickness. This thickness can be measured with a PTG.
In many cases the total paint thickness on a new vehicle will have an average of roughly 120 microns. And in some cases, this is fairly evenly divided in the three layers. Giving a primer coat of roughly 40 microns, a colored coat of another 40 microns and a clear coat of roughly 40 microns.
However, in most cases it will differ a bit. Since the thickness of paint is applied either by hand or by robots, the thickness depends totally on how much paint actually lands on the surface. This is never precisely the same on every spot. Paint thickness can vary within an are of just a square centimeter. The thickness of paint on panels can also be very different. The hood might give a total thickness reading of 100 micron, while the drivers door gives a reading of 80 micron.

PTG or paint thickness gauge

There are a few devices that can measure the thickness of paint. These are called paint thickness gauges, or PTG for short. They might also be referred to as PDG or paint depth gauge. The aim is to provide the user with information that tells him how much paint he has to work with. Telling him how safe it is to polish out those swirls.

Thickness and colors

There are a few misconceptions regarding paint, such as the idea that a certain color needs to be applied thicker then other colors. This is not true. There can be varies reasons why paint is applied more thick (for example a custom paint job), but there is no reason to apply a certain color more thick then others.

Paint thickness and re-sprays

When a car gets re-sprayed, they can decided to sand the car down and re-apply the total paintjob, or thery can sand off the clear coat, re-apply the colored coat and then re-apply a clear coat.
In the first situation, the paint thickness won’t be very much different to the original thickness. But in the last situation, the paint thickness is much more then the original layer. Because now you have a primer, a colored coat another color coat and then a clear coat.
When taking measurements on a vehicle, you can encounter panels with a paint thickness of over 200 microns. Which, in most cases, indicates a re-spray.

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