9H Hardness = Scratch-Proof
Quick answer: 9H refers to the pencil hardness test (ASTM D3363) and means a cured coating resists being scratched by a 9H pencil under specified conditions. It does not mean Mohs 9 or that the surface is scratch-proof in real-world use.
What it means
The pencil test uses graded graphite pencils (from soft 6B to hard 9H) pushed across a coated panel at a fixed angle and load. If a coating “passes 9H”, the 9H pencil does not cut a visible groove under that test. This measures a narrow kind of mar resistance on a flat test panel – not resistance to grit dragged under a wash mitt, keys, or stone chips. Mohs hardness (talc=1, diamond=10) is a different scale entirely and is not used for automotive coatings.
Why it matters
- Expectation setting: prevents confusing a lab scratch-resistance test with real-world immunity to marring.
- Apples-to-apples: 9H ratings are common across many ceramics – technique, cure and film uniformity matter more.
- Process focus: safe washing and drying reduce marring far more than chasing a higher “H” on the label.
- Specification literacy: look for supporting data (chemical resistance, durability, contact angle) not a single headline number.
Where you’ll see it
Marketing for ceramic coatings and dealer packages, often presented as “9H ceramic hardness” or “as hard as diamond”.
Context
Car Paint Protection; Ceramic coatings; Marketing claims
Common mistakes
- Taking 9H as Mohs 9 – it is a different scale. Mohs 9 is corundum, not achievable by wipe-on coatings.
- Assuming scratch-proof – coatings resist light marring but will not stop keys, grit or chips.
- Comparing brands by 9H alone – many pass 9H; prep quality and application technique dominate results.
- Ignoring test conditions – load, angle and cure time affect outcomes and may not match real use.
- Using 9H to justify poor wash habits – bad technique will still mark the surface.
Written by Danny Argent. Last updated 07/11/2025 15:04