My Cart


MOHS & Pencil hardness Testing

Posted on

“How hard is your coating?” The inevitable question asked by anyone new to FEYNLAB™ products, and an extremely difficult question to answer.

Let’s start with a little background on both pencil hardness and the infamous MOHS scale. The pencil hardness method was originally developed by pencil manufacturers as a quality control method in the early 1900’s, if two different pencils cause the same scratch damage to a coating then they are considered the same hardness, simple. The coatings industry adopted this in a reverse manner and starting using variations of standardized pencil hardness to measure their coating hardness.

Fast forward to the modern day and it has become an important, yet misleading, marketing tool for companies that supply vehicle protection coatings, i.e. “Ceramic” and “Glass” and other “Nano coatings”. Ever wondered why a supposedly 9H coating can be scratched with just a fingernail?

“But it’s [insert independent test company] certified!”

The test data used by these companies are valid for the tests that they have done, we’re not disputing that. But if you take a more subjective look you will see that they have coated a steel plate and ran it through the test, it results in a very high number, usually 9H (the maximum allowable under ASTM and BS standards). But the substrate becomes an overriding factor when testing thin films, these coatings are usually less than 5 microns and there is no-way you would get a reading of the film hardness. You are testing the hardness of the steel underneath the coating.

There have been independent studies done showing that depending on the substrate, the hardness can change by 13H values. Please find a results table from such a study below.

George E. Drazinakis and Agnes Lechwar)

It is clear from the table above that the hardness value is significantly different when comparing PC (Polycarbonate) and (polymethyl methacrylate) as substrates.

Many companies shy away from the “9H” rating, I suppose it is a long term strategy as customers and installers start being more educated, they will learn that the 9H is an utter lie. So instead they claim 7H or some lower number. And this is even more bizzare as they are actually claiming that their product is worse on a rigged scale? Wow.
There are also suppliers claiming 10H or even 11H… I won’t even comment on these…

Then there is the MOHS scale, where some companies and their representatives claim that their product is 9H on the MOHS scale. If this were true you should be able to score Glass with a dried sample, I guarantee you this is not the case. We should simply assume that they don’t understand their product well enough, nor have the ability to understand the difference between Pencil Hardness and the MOHS scale. Their ignorance could very well land them with severe fines, or even jail time?, last time I checked false advertising was still illegal. As an installer, selling and marketing products using the same falsities makes them equally liable. I don’t know if many installers realize this. Also when a product (coating) fails, the customer does not complain to the coating supplier, it is the installer that is left holding the bag, and their reputation is at stake.

The most correct test method would be to compare an un-coated automotive paint sample, with a coated sample. And do a test before and after using the pencil hardness (or more preferably nano indentation). Why has no-one done this, or why has no-one released test data on this? Well because the change is almost immeasurable.


Leave a comment

All blog comments are checked prior to publishing

Hello You!

Join our mailing list