Mesh Size vs Microns: Understanding Particle Size Distribution in Minerals
- by Omega Fine Products
In industrial minerals, clarity around grading terminology is essential. Terms such as mesh size, micron equivalent and particle size distribution (PSD) are often used interchangeably in conversation, yet they describe different aspects of material classification.
Having supplied industrial minerals to formulators across paints, construction and polymer applications for over 10 years, we’ve found that misunderstandings around grading terminology are one of the most common causes of specification errors and avoidable reformulation costs.
For formulators in paints, plastics, construction materials and specialised industrial applications, understanding these distinctions directly affects processing efficiency, product performance and cost control.
This article explains how mineral grading systems work and why particle size distribution matters more than nominal size alone, using examples of silica, dolomite and calcium carbonate grades supplied by Omega Fine Products.
Mesh size refers to the number of sieve openings per linear inch and only guarantees that material passes through a specified screen. Micron grading, measured via laser diffraction, provides D10, D50 and D90 values that describe the actual particle size distribution, giving formulators far more useful information about how a mineral will perform in their application.
D50 is the median particle size, 50% of particles are smaller than this value. D90 means 90% of particles are smaller than this value. Together with D10, these values describe the full spread of the particle size distribution. In most coating and polymer applications, the D90 is the more critical specification, as the coarser fraction has the greatest influence on surface finish, viscosity and equipment wear.
Two minerals carrying the same nominal size label, for example “20 micron”, can behave very differently depending on the width of their particle size distribution and their top-cut value. PSD directly affects packing efficiency, rheology, binder demand, surface finish and abrasion in processing equipment. Specifying only a D50 value without confirming D90 and D10 is one of the most common causes of unexpected performance variation in paint and plastics formulations.
Request full PSD data, D10, D50 and D90, rather than a nominal size alone. Confirm the top-cut value if equipment wear is a concern. Evaluate oil absorption alongside particle size, as a narrow versus broad distribution grade of the same mineral can significantly affect binder demand and viscosity. Aligning PSD with your target packing density and rheology requirements will give you more predictable and consistent results batch to batch.
Mesh Size: The Traditional Screening System
Mesh size originates from mechanical screening. It refers to the number of openings per linear inch in a sieve screen.
- 10 mesh = 10 openings per inch (coarser)
- 100 mesh = 100 openings per inch (finer)
- 325 mesh = 325 openings per inch (very fine)
The higher the mesh number, the smaller the aperture.
Important: Mesh size describes the sieve opening, not the actual particle size distribution of the final product. After milling, particles may be irregular, fractured or agglomerated. Mesh grading only guarantees that material passes through a specified screen.
For example:
- A 200 mesh silica grade from Omega Fine Products ensures material passes 75 µm.
- It does not guarantee all particles are exactly 75 µm.
In practice, we regularly see customers specifying a 200 mesh product when their application actually requires a controlled D90 — the mesh grade passes the screen, but the fine fraction behaviour is what determines performance in the finished product.
Micron Grading: Average Particle Size
Modern mineral grading increasingly uses micron-based classification, typically measured via laser diffraction (ISO 13320).
Common reported values include:
- D10 – 10% of particles are smaller than this size
- D50 – Median particle size
- D90 – 90% of particles are smaller than this size
Example: A calcium carbonate grade may have:
- D50 = 10 µm
- D90 = 25 µm
This tells us far more than a simple “10 micron product” label.
Micron grading is especially important in coatings, sealants, plastics and adhesives where rheology, packing density and surface smoothness are influenced by fine fractions.
When customers send us a competitor’s product for comparison, the D90 value is almost always where the meaningful difference lies — two products with identical D50 values can behave very differently in a coating once you examine the full distribution curve.
Why Particle Size Distribution (PSD) Matters More Than Nominal Size
Nominal size (for example, “15 micron”) is typically shorthand for the D50 value. However, performance is governed by the full particle size distribution curve, not just the median.
Key Reasons PSD Is Critical
- Packing Efficiency
A well-distributed mix of coarse and fine particles improves packing density. This:
- Reduces void space
- Improves mechanical strength
- Lowers binder demand in paints and polymers
- Rheology Control
Fine particles increase surface area and oil absorption. Too many fines can:
- Increase viscosity
- Raise binder demand
- Reduce workability
We’ve seen this directly in water-based paint systems where a shift in the fine fraction of a calcium carbonate grade, without any change to the nominal D50, caused a measurable increase in viscosity that required reformulation.
- Surface Finish
Narrow PSD improves:
- Film smoothness in coatings
- Surface quality in cast products
- Dispersion stability
- Abrasion & Hardness Control
In silica systems especially, oversized particles can increase abrasion in processing equipment.
In practical terms, two minerals both labelled “20 micron” may behave very differently depending on their PSD width and top-cut.
Examples from Omega Fine Products
Omega Fine Products supplies graded silica, dolomite and calcium carbonate tailored to industrial specifications.
Silica Grades
Silica (SiO₂) is commonly supplied in:
- Screened mesh grades (e.g., 150 mesh, 200 mesh)
- Micronised grades with defined D50 and D90 values
In construction and flooring systems, mesh control may be sufficient. In coatings and polymer systems, micronised silica with controlled PSD is typically required for predictable rheology and surface performance.
Dolomite Grades
Dolomite (CaMg(CO₃)₂) is valued for:
- Moderate hardness
- Balanced oil absorption
- Controlled particle morphology
Omega Fine Products supplies dolomite in both coarse screened aggregates and fine micronised grades for paint and compound applications. PSD strongly influences:
- Scrub resistance in coatings
- Dispersion behaviour
- Cost optimisation through extender loading
“Dolomite PSD is the specification point most frequently underestimated by formulators switching from calcium carbonate — the difference in oil absorption between a broad and narrow distribution grade can significantly affect loading levels and cost-in-use.”
— Frederich Vorster, COO, Omega Fine Products
Calcium Carbonate Grades
Calcium carbonate (CaCO₃) is one of the most widely used mineral fillers globally. Available grades may range from:
- Coarse 100–200 mesh material
- Fine 5–15 micron D50 products
- Ultra-fine grades below 5 microns
For paints:
- Broader PSD may enhance packing efficiency.
- Narrow PSD improves gloss and smoothness.
For plastics:
- Controlled top-cut reduces die wear and improves extrusion consistency.
The performance difference between two “10 micron” calcium carbonate grades is often determined by D90 and fine fraction percentage rather than D50 alone. There is also variance around naming conventions in different countries — take care.
“We encounter this regularly when working with customers importing specifications from North African formulation teams — what is labelled a ‘10 micron’ grade in one market may have a substantially different D90 than a product carrying the same label from a different supplier or region.”
— Frederich Vorster, COO, Omega Fine Products
Comparing Mesh vs Micron vs Full PSD
Conclusion
- Mesh grading ensures basic screening compliance.
- Micron grading improves accuracy.
- Full PSD control delivers predictable performance.
Practical Guidance for Specifiers
The guidance below reflects what we’ve learned from supporting formulators across a wide range of industrial applications — the specifications that matter most are rarely the ones printed largest on a datasheet.
When selecting mineral grades:
- Request D10, D50 and D90 values — not just a nominal size.
- Confirm top-cut limits for wear-sensitive applications.
- Evaluate oil absorption alongside PSD.
- Align PSD with target packing density and rheology requirements.
- Ensure consistent sourcing and quality control.
Omega Fine Products provides technical data sheets with PSD curves and physical property specifications to support formulation decisions.
Learn More
For further technical insights, explore related Omega Fine Products mineral resources:
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