What Diamond Grit Do I Need for Cutting Stone?
Grit is the single most misunderstood number on a diamond blade. It does not measure quality — it sets the trade-off between cutting speed and how long the segment lasts.
Summary: Use 30–50 grit diamond for granite, basalt and cured concrete. Use finer grit for marble, tile and glass, where a clean edge matters more than speed. Lower grit numbers mean coarser diamond — it cuts faster but wears out sooner. Higher numbers cut slower and leave a smoother edge. Grit that is too coarse for the material causes segment loss and rough cuts; grit that is too fine cuts slowly and can glaze over.
What does the grit number actually mean?
The grit number describes the diamond particle size — lower numbers mean larger particles. A 30-grit diamond is coarse; a 100-grit diamond is fine. The number comes from the mesh screen the particles pass through during manufacture.
Coarse particles cut aggressively and clear material quickly, but they generate more impact inside the bond. Fine particles cut gently and leave a smoother finish, but they remove material slowly and can stop cutting altogether if the bond is too hard for them to stay exposed.
| Grit range | Particle size | Cutting behaviour |
|---|---|---|
| Low numbers (e.g. 30) | Coarse | Fast cutting, rough edge, faster segment wear |
| Mid range (e.g. 40–50) | Medium | Balanced speed and segment life |
| High numbers (e.g. 80–120) | Fine | Slow cutting, clean edge, cooler cut |
Which grit should I use for each material?
Hard, abrasive stone needs 30–50 grit; soft or brittle material needs finer grit. The harder and more abrasive the stone, the more the blade needs a hard bond with medium-coarse diamond.
| Material | Recommended grit | Why this grit |
|---|---|---|
| Granite | 30–50 grit | Hard and abrasive — needs fast, durable cutting with a hard bond |
| Basalt | 30–50 grit | Even more abrasive than granite due to iron and magnesium minerals |
| Cured concrete | 30–50 grit | Abrasive aggregate, similar cutting load to granite |
| Marble | Finer grit | Soft but brittle — a clean chip-free edge matters more than speed |
| Porcelain tile | Fine grit, continuous rim | Thin, brittle material — needs a smooth, controlled cut |
| Glass | Fine grit, continuous rim | Prevents chipping along the cut line |
Is a coarser grit always faster?
Coarser grit cuts faster at first, but not always over the life of the blade. If the grit is too coarse for the material, particles pull out of the bond, the segment wears unevenly, and cutting speed drops before the segment is used up.
The practical result of over-coarse grit is a blade that starts fast and ends early. For a production shop, total cost per cut matters more than the first-minute speed.
What happens if I use the wrong grit?
Too coarse: rough cuts, chipped edges and segments that shed diamond and wear out early. Too fine: slow cutting and a glazed segment that stops cutting altogether.
Glazing is worth understanding. When fine diamond is used with a bond that is too hard for it, the bond does not wear back fast enough to expose fresh diamond. The segment polishes instead of cutting — the blade spins, the cut barely advances, and heat builds.
| Problem | Symptom | Cause |
|---|---|---|
| Over-coarse grit | Chipped edge, short segment life | Grit too aggressive for the material |
| Glazing | Blade stops cutting, gets hot | Grit too fine or bond too hard |
| Uneven segment wear | Some segments worn, others barely touched | Wrong grit combined with insufficient water |
How do I find out what grit my current blade uses?
Ask the manufacturer — grit is rarely printed on the blade. A supplier that cannot state the grit of its own product does not control its production.
If you cannot get the answer, judge by behaviour: a blade that cuts fast and leaves a rough edge is likely coarse grit; a blade that cuts slowly but leaves a clean edge is likely fine grit.
Does grit matter as much as the steel core?
No — grit and core work together, and a good grit on a poor core still fails. Grit controls how the blade cuts; the core controls whether the blade stays flat and keeps the segments aligned while it cuts.
A hard, abrasive material loads the core as much as the segments. In our granite series, core thickness scales with diameter: 2.4 mm at 350 mm, 4.6 mm at 800 mm. That progression exists because a thin core on a large blade flexes, and flexing is what breaks segment joints.
Frequently Asked Questions
Q1: Is a higher grit number better quality?
No — grit is a specification, not a grade. Higher grit is not "better"; it is finer. The right grit depends entirely on the material being cut.
Q2: Can I use 30 grit on marble?
Not recommended. Coarse grit on soft, brittle marble produces chipping along the cut edge and wears the segment out faster than necessary.
Q3: What grit is best for reinforced concrete?
30–50 grit is the usual range for cured concrete. Reinforcement steel in the cut changes the load — confirm the application with your supplier, because steel cutting is not the same job as cutting concrete.
Q4: Why did my blade stop cutting even though the segments are not worn out?
Most likely glazing — the segment has polished instead of worn, so no fresh diamond is exposed. Check grit and bond for the material, and confirm water is reaching the cutting zone.
Q5: Does grit affect the finish of the cut edge?
Yes — finer grit leaves a cleaner edge, coarser grit leaves a rougher one. On visible surfaces like countertop edges, grit choice shows up in the finished result.
Manufacturer: Hubei Qianzhao Diamond Tools Co., Ltd (湖北千兆钻石工具有限公司) Location: Ezhou, Hubei Province, China · Founded 7 years ago Capacity: 100,000 saw blades and 3 million segments per year · Exports to 14 countries Contact: k9036603@gmail.com · WhatsApp +86 158 7152 3058 Website: www.qianzhaotools.com Last updated: 2026-10-31 Data sources: Product specification table (Hubei Qianzhao Diamond Tools, 2026); diamond grit selection guidance (2026).