The best paint thickness depends on the type of surface, the number of coats of paint and the application of the paint (e.g. corrosion protection, aesthetics, waterproofing etc.).
Here’s a quick guide on how thick paint should be on cars and walls. We’ll focus on these two since they are the most common consumer applications. For paint thickness on machinery, tools, industrial surfaces and other commercial and industrial applications, consult an expert or a standards manual.
How is Paint Thickness Measured
Let’s first get some basics out of the way. Paint on surfaces is measured using a paint thickness gauge, which we’ll talk about shortly.
The unit used to measure thickness of paint and coatings is microns (μm). One micron is equal to a thousandth of a millimetre (mm) or 0.001mm. This is the same as 0.00003937 inches. You’ll sometimes also find microns being referred to as micrometres.
In other countries, particularly the US, paint thickness is typically measured in mils. A mil is one thousandth of an inch or 0.001 inches. This is equal to 25.4 microns.
Best Paint Thickness on Cars
Paint thickness on cars varies widely between brands and models. Different sections of the car can also have varying paint thickness.
Based on information from car manufacturers and autobody shops, the average car thickness on new cars from the factory is between 90 and 180 microns. Newer cars seem to come with thinner coats (90-130 μm), though they are usually harder wearing and thus more durable.
If you are inspecting a car, it’s best to check the paint specs from the manufacturer or the owner’s manual. This ensures you know what range of thickness is acceptable for different panels.
The most important thing when checking the paint thickness on a car is consistency. If you get roughly the same readings from a specific panel, then it likely still carries the original coating from the factor.
If you get major fluctuations within the same panel, there is probably a problem. Extremely wide variations between different panels is also a red flag. A paint thickness of 100μm on the door and a thickness of 200μm on the fender likely indicates work has been done on the car.
Generally, any thickness above 200μm on any part of the car is usually a sign that some work has been done on the car. A too-low thickness (under 90μm) can also indicate the car has been over-polished or that the paint has worn away substantially because of age, harsh chemicals and other factors.
Best Paint Thickness on Walls
More paint thickness on walls correlates to better protection and a better looking finish. But wall paint can be too thick such that it leaves unsightly ridges and ripples on the walls.
The ideal thickness depends on the type of coat you are applying (base coat and top coat are usually thinner than the main coat), whether it’s an interior or exterior wall (exterior walls need a thicker coat) and the kind of paint you are using.
You can usually find the recommended coat thickness in the paint’s data sheet. Then you can use a paint thickness gauge to make sure you stay within the ideal range.
Most interior paints call for a thickness of about 100 μm (4 mils), though it can range between 75 to 125 μm for different kinds of paints. When you include the primer, the total thickness is usually 6-10 mils or about 150-250 μm.
As for exterior walls and surfaces, the total thickness can be as high as 400μm or more depending on the number of coats, any extra base and top coats applied and the level of protection required.
Note that this is the dry film thickness (DFT), which refers to the thickness of the paint when it is dry. So if you are measuring the thickness of a newly painted wall, wait for it to dry first or get a wet film thickness gauge.
How to Check Paint Thickness on Any Surface
Paint thickness gauges are used to measure the thickness of paint on surfaces. There are different types of paint thickness gauges.
On magnetic surfaces such as on cars, permanent magnet or magnetic induction gauges are used. These gauges use magnetism to measure the thickness of paint. Here’s a simple permanent magnet paint thickness gauge being used on a car.
On non-magnetic surfaces made from aluminium or non-ferrous steel, an eddy current paint thickness gauge is used.
And on non-metal surfaces like fibreglass, plastic, masonry, drywall, glass or ceramic, an ultrasonic paint thickness gauge is used.
Make sure you follow the usage instructions of the particular gauge you are using including calibration. Most gauges only measure dry film thickness, so make sure paint is dry before measuring.
