Calcium Carbonate Filler Grades: Which Fineness to Specify
A mesh number only says what a sieve lets through, so specify calcium carbonate fillers by D50, top cut and test method instead. Then set the chemistry, moisture and coating your end use needs: tight top cut for paint, coating and low silica for rigid PVC, low moisture for sealants. Prove any new grade in four stages before switching.
Two bags both say 400 mesh. One paint batch draws down smooth. The other shows specks on the Hegman gauge.
Both labels can be true. Mesh says what a sieve lets through, not what the powder is mostly made of.
Calcium carbonate filler grades differ in three ways: fineness, purity and surface treatment. Specify fineness as a median size (D50) plus a top cut (D97 or D98) with the test method, not as mesh alone. Then set CaCO3, iron, moisture and whiteness for the end use, and confirm the grade in a plant trial.
This note covers fineness, spec lines by end use, coating and trials.
What a calcium carbonate filler does
A calcium carbonate filler is finely ground calcite or marble added to polymers, paints and sealants.
This ground form is called ground calcium carbonate (GCC). The Indian Bureau of Mines notes its wide use in plastics, paper, rubber and paint.
In PVC, it reduces shrinkage and adds dimensional stability. PVC processing guidance from Indian consultancy Kanademy notes the cost: higher melt viscosity, slower pipe extrusion, lower tensile strength.
In moisture-curing sealants, one producer puts filler at up to 55–60% of the formulation.
Precipitated calcium carbonate (PCC) is the same compound made chemically; see ground and precipitated calcium carbonate compared.
Mesh, D50 and top cut: how to read fineness
Mesh is the number of sieve openings per linear inch. Use the table below, from ASTM E11 as tabulated by Gilson, to translate mesh into microns (µm).
| Mesh (ASTM E11 sieve No.) | Sieve opening (µm) |
|---|---|
| 100 | 150 |
| 200 | 75 |
| 325 | 45 |
| 400 | 38 |
Indian standards name sieves by their opening in microns (IS 460 (Part 1):1985). So a "63 micron IS sieve" and a 230 mesh sieve are the same idea.
Mesh describes only the coarse end of the particle size distribution (PSD). D50 is the median particle size: half the sample is finer. Top cut (D98 or D97) is the size that 98% (or 97%) of the sample is finer than. Werner (2000) defines top cut by weight, from sedimentation; laser diffraction reports by volume.
Omya's published data for one coarse grade shows why mesh alone misleads: a D50 of 100 µm, yet 60% stays on a 200 mesh sieve.
So a fineness line should give D50, top cut, residue on a named sieve, and the method.
IS 63:2006, the Bureau of Indian Standards (BIS) specification for whiting for paint and putty, allows Grade 2 at most 0.2% residue on a 37 µm sieve. A good 400 mesh powder may pass that. Grade 2 also needs 96% finer than 10 µm, which only a PSD shows.
Calcium carbonate filler grades by end use: which spec lines matter
Find your row. The second column is a published reference point, not a target.
| End use | Published fineness reference | Spec lines that matter most | Why |
|---|---|---|---|
| Paint (IS 63 Grade 2, crystalline) | ≥ 96% finer than 10 µm; ≤ 0.2% on 37 µm | Top cut, residue, oil absorption, whiteness | Coarse particles show in emulsion films |
| Putty and paint (IS 63 Grade 1, amorphous) | ≤ 0.5% on 63 µm; oil absorption 13–22 | Residue, colour, water demand | Workability, finish and colour |
| Rigid PVC pipe and profile | D50 about 1–7 µm; top cut about 6–25 µm | Top cut, coating, moisture, silica | Finer helps impact; silica abrades screws |
| Plasters, joint fillers, flexible PVC | Coarse grades: D50 about 100 µm | PSD consistency, moisture | High loadings magnify batch drift |
| Moisture-curing adhesives and sealants | Fine, surface-treated grades | Moisture, moisture pick-up, coating | Water in the filler starts curing early |
Reference points from Omya product data sheets (typical values, not specifications) and IS 63:2006. Final specifications should always be confirmed by the buyer's technical or quality team.
Purity, iron and whiteness
Purity sets the ceiling on whiteness: the Indian Bureau of Mines notes that calcite above 98% CaCO3 has the highest brightness.
Iron oxides and organic matter both lower lightness and add yellow and red, with organic matter the stronger effect (Christidis et al., 2004). Silicate impurities, at up to Mohs 6 against calcite's 3, abrade extruders.
IS 63 judges whiteness against an approved sample. For general limits, see what CaCO3, MgO, SiO2 and Fe2O3 limits mean. How each line is measured and reported is covered in how to read a calcium carbonate certificate of analysis.
PVC pipe for drinking water
IS 4985:2000, the BIS standard for unplasticized PVC pipes for potable water, caps the pipe's sulphated ash at 11% and sets its density at 1.40–1.46 g/cm3. A 2021 revision is current, so check its clause before quoting a limit. These checks in practice limit how much filler a potable-water pipe can carry.
Coated or uncoated?
A coated grade is treated with a fatty acid, usually stearic acid. Untreated calcium carbonate has a water-loving surface that mixes poorly with polyethylene and polypropylene, a 2025 study in Scientific Reports notes. Stearic acid changes how particles wet and disperse.
Processors commonly use coated grades for rigid PVC and uncoated grades for plasticized PVC. Moisture-curing sealants use surface-treated grades for low moisture pick-up. IS 63 sets no coating requirement.
Before accepting a coated grade, ask which agent, at what level, and whether the PSD was measured before or after coating.
How to trial a new filler without disrupting production
Run these four stages in order, and keep the current filler in reserve until stage 4 is signed off.
| Stage | What to do | What to check |
|---|---|---|
| 1. Write the spec | Set D50, top cut, method, chemistry, moisture, coating, colour sample | Each line confirmed as a limit, not a typical value |
| 2. Lab check | Test the sample against its CoA and your current filler | Same lab and method: PSD, residue, moisture, colour |
| 3. Bench or pilot batch | Make your product at the current loading | Viscosity or melt behaviour, colour; pipe density and ash |
| 4. Plant trial and lot approval | One line, one defined run, then several consecutive lots | A certificate of analysis (CoA) per lot; retained samples |
A trial that passes once proves the sample. Several steady lots prove the supply.
Where Dr. Lime fits
CalFill is Dr. Lime's ground calcium carbonate filler, published at 100–400 mesh with a D50 of 30–100 µm, with custom micron grades and controlled fines and oversize available. Its published chemistry is CaCO3 ≥ 95%, MgO ≤ 1.5%, Fe2O3 ≤ 0.15%, Acid Insoluble ≤ 1.5% and Moisture ≤ 0.5%. Listed uses: polymer and rubber compounding, industrial coatings, adhesives and construction fillers.
It comes from a single-source deposit and is processed at Dr. Lime's ISO 9001:2015-certified plant in Nagaur, Rajasthan, which has its own laboratory. Particle size distribution is measured by volume using laser analysis, with lot-level traceability.
See calcium carbonate fillers for polymers, coatings and adhesives and Dr. Lime's validation process.
The Dr. Lime team can share specifications, compare against your current filler's particle size distribution, and arrange a trial sample.
Specify the curve, not the mesh
Mesh gives the largest particle a sieve lets through. Your product responds to the whole curve. Specify D50, top cut and method, then prove the grade on your line.
The mesh is printed on the bag. The curve is what your product feels.
FAQs
What is the difference between mesh size and D50 for calcium carbonate?
Mesh size names the sieve a powder passes, for example 400 mesh, a 38 µm opening under ASTM E11. D50 is the median particle size: half the sample is finer. Mesh describes only the coarse end, while D50 and a top cut (D97 or D98) describe the distribution. Always ask which method measured them.
Which calcium carbonate grade is used in PVC pipes?
Rigid PVC pipe usually takes a fine, coated ground calcium carbonate with a controlled top cut, low moisture and low silica. Published rigid-PVC grades run at a D50 of about 1–7 µm. For potable-water pipe in India, IS 4985 also limits the pipe's sulphated ash and density, which in practice limits filler loading.
Is 400 mesh calcium carbonate fine enough for paint?
A 400 mesh calcium carbonate may pass the sieve-residue checks in IS 63, the Indian standard for whiting for paint and putty. But IS 63 Grade 2 also requires at least 96% of the powder to be finer than 10 µm, which a mesh name cannot show. Ask for D50, top cut and residue on a named sieve.
What is coated calcium carbonate and when is it needed?
Coated calcium carbonate is ground calcium carbonate treated with a fatty acid, usually stearic acid, so it disperses in water-repelling polymers. PVC processors commonly use coated grades for rigid PVC and uncoated grades for plasticized PVC. Moisture-curing sealants use surface-treated grades for low moisture pick-up. Ask for the coating agent and level.
Why does a calcium carbonate filler look off-white?
A calcium carbonate filler usually looks off-white because of impurities. Iron oxides and organic matter both lower lightness and add yellow or red tones, and in one published study organic matter had the stronger effect. Judge whiteness against an approved sample, measured by the same method each time.
What is oil absorption in calcium carbonate, and why does it matter?
Oil absorption is the amount of linseed oil needed to turn a set mass of filler into a paste. It indicates how much binder a paint or putty needs. IS 63 sets 13–22 for Grade 1 whiting and 15–25 for Grade 2, within ±10% of an approved sample. Higher oil absorption usually means more binder and higher viscosity.
How much moisture is acceptable in a calcium carbonate filler?
Acceptable moisture depends on the end use. IS 63 allows up to 0.50% volatile matter in whiting for paint and putty. Moisture-curing sealants are far stricter, because water carried in by the filler can start curing in the pack. Set the limit with your formulator and check it on every lot.
Does Dr. Lime supply calcium carbonate filler?
Yes. Dr. Lime makes CalFill, a ground calcium carbonate filler published at 100–400 mesh with a D50 of 30–100 µm, CaCO3 ≥ 95% and Fe2O3 ≤ 0.15%. Custom micron grades are available. The Dr. Lime team can share specifications and arrange a trial sample.
