About Dolomite Powder (200 / 325 Mesh)
Dolomite powder is raw, uncalcined dolomite ground and air-classified to 200 mesh (75 µm) or 325 mesh (45 µm). It keeps the full carbonate composition of the mineral, around 30 % CaO and 21 % MgO, and its rhombohedral particles give a bright, low-oil-absorption filler that disperses readily in water-borne and solvent-borne systems.
In decorative and industrial paints, dolomite powder is used as an extender alongside, or in place of part of, the calcite. It adds body, helps sag resistance and lowers raw material cost per litre, while its slightly higher hardness than calcite gives firmer films with better scrub resistance in exterior and textured finishes. In ceramics, the powder is a combined source of lime and magnesia. In wall tile bodies it forms calcium–magnesium silicate phases during firing that help limit moisture expansion, and in glazes it acts as a flux that contributes to satin and matt surfaces.
Obsidian Minerals controls whiteness, iron content and top-size residue from batch to batch, because these are the properties that shift paint shade and fired colour. Both mesh sizes are offered as standard, each lot is released against a batch Certificate of Analysis, and finer cuts can be developed with customers on request.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| CaO | 29.5–31.0 % | ASTM C25 |
| MgO | 20.0–21.5 % | ASTM C25 |
| SiO₂ | ≤ 1.0 % | ASTM C25 |
| Fe₂O₃ | ≤ 0.15 % | ASTM C25 |
| Brightness (GE) | ≥ 85 | Internal method |
| Residue on sieve | ≤ 1.0 % on 75 µm (200 mesh grade); ≤ 2.0 % on 45 µm (325 mesh grade) | ASTM D185 |
| Oil absorption | 14–20 g/100 g | ASTM D281 |
| Moisture | ≤ 0.5 % | Internal method (105 °C) |
Typical values for guidance. Guaranteed limits for each mesh size are stated on the Technical Data Sheet and batch CoA.
Key features & benefits
Two standard mesh sizes
The 200 mesh grade suits ceramic bodies and economy fillers, while 325 mesh dolomite powder serves paints, glazes and putties that need a smoother finish and a lower top-size residue.
High whiteness, low iron
Typical GE brightness of 85 or higher and Fe₂O₃ of about 0.15 % or less help keep paint shades clean and limit discolouration in light-firing ceramic bodies and glazes.
Low oil absorption
The powder takes up relatively little binder, so formulators can raise filler loading in emulsion and alkyd paints without a sharp rise in viscosity or binder demand.
Combined CaO and MgO flux
In ceramic bodies and glazes the powder supplies lime and magnesia from a single raw material, which simplifies batch calculations and helps develop matt and satin glaze surfaces.
Firm, durable films
With a Mohs hardness of about 3.5–4, dolomite adds firmness to dried paint films and helps exterior and textured coatings resist scrubbing and surface abrasion.
Applications
Decorative and exterior paints
An extender in emulsion and textured paints, where it builds solids, supports anti-sag behaviour and helps control cost per litre while keeping a clean white base for tinting.
Wall and floor tile bodies
Added to wall tile bodies as a CaO–MgO source that reacts during firing, helping to control moisture expansion and the dimensional stability of the fired tile.
Ceramic glazes
A flux for matt and satin glazes, in which the magnesia component can contribute a smooth, buttery surface texture at tile and stoneware firing temperatures.
Putties, primers and fillers
A bright, easily dispersed filler for wall putty, primers, joint compounds and sealants where whiteness and controlled fineness matter more than very fine particle size.
Usage & handling
- In paints, typical loading is about 10–35 % of the formulation, set by the target pigment volume concentration and the other extenders used.
- In wall tile bodies, dolomite is commonly used at around 5–15 % of the body recipe; glaze additions follow the glaze formula.
- Disperse into the mill base under high-speed mixing; no pre-treatment is needed.
- Store bags on pallets in a dry, covered area and keep them closed to avoid moisture pick-up and contamination.
Packaging & supply
- 25 kg and 50 kg HDPE or paper bags, palletised on request
- 1 MT and 1.2 MT jumbo bags for paint and tile plants buying in bulk
- Private-label packaging available on request
Frequently asked questions
What is the difference between 200 mesh and 325 mesh dolomite powder?
The mesh number indicates the sieve the powder is classified to pass. 200 mesh corresponds to 75 µm and 325 mesh to 45 µm, so the 325 mesh grade is finer, with less coarse residue. Use 200 mesh for ceramic bodies and general fillers, and 325 mesh for paints, glazes and putties that need a smoother surface.
Can dolomite powder replace calcium carbonate in paint?
In many emulsion and textured paints, dolomite powder can replace part or all of a comparable calcite extender. It has similar brightness and low oil absorption, with slightly higher hardness that can improve scrub resistance. Because particle size and surface chemistry differ, customers should run a ladder trial to confirm viscosity, sheen and opacity before switching fully.
Why is dolomite used in wall tile bodies?
During firing, dolomite decomposes and its lime and magnesia react with clay and silica to form stable crystalline silicate phases. These phases help the porous wall tile body resist moisture expansion over time and keep its dimensions stable. Dolomite also contributes to a light body colour when iron content is low.
What iron content does your dolomite powder have?
Typical Fe₂O₃ is 0.15 % or less, which supports clean white paints and light-firing ceramic bodies. Lower-iron selections can be discussed for glazes and sensitive applications. Guaranteed iron limits for your order are stated on the Technical Data Sheet, and each batch Certificate of Analysis reports the measured value.
Is dolomite powder the same as calcined dolomite?
No. Dolomite powder is the raw carbonate mineral, finely ground, and it still contains its carbon dioxide, giving a loss on ignition of about 46–47 %. Calcined dolomite has been heated to remove that CO₂ and is a reactive oxide used in steelmaking. For paints, putties and ceramic bodies, the uncalcined powder is the correct choice.