Choose calcium carbonate for the performance of the complete paint, not for a single purity or brightness number. A useful shortlist combines the required particle-size distribution, surface characteristics and handling properties with a controlled trial in your own binder and pigment system.
This guide concerns ground calcium carbonate (GCC) for industrial and decorative coatings. It is a starting point for a technical enquiry, not a fixed formulation or a promise that one filler grade will perform equally in every paint.
What does calcium carbonate do in paint?
GCC is used as a mineral filler or extender. The selected grade can influence the coating’s optical properties, surface finish and formulation behaviour. Omya’s coatings guidance distinguishes grades by particle size and the performance required in decorative or industrial systems. This is why “paint grade” alone is an incomplete specification.
Start with a short description of the product: water-based or solvent-based, interior or exterior, matt or gloss, and the substrate. Then name the property you need to improve. “Reduce cost while maintaining our scrub-resistance result and contrast ratio” is more useful than “send your best quality.”
Which properties should the purchase specification contain?
| Property | What to request | How to compare it |
|---|---|---|
| Particle-size distribution | Median size, upper-tail value and the measurement method. | Use the same percentile and method; do not equate d97 with d98. |
| Optical properties | Brightness or whiteness, colour coordinates where relevant, and test method. | Compare like-for-like results alongside a drawdown in the actual paint. |
| Oil absorption | Result, units and test procedure. | Keep this separate from measured viscosity in your finished formulation. |
| Moisture and residue | Agreed limits and the sieve or other residue method. | Connect the limits to incoming inspection and production requirements. |
| Surface and supply form | Untreated or treated material; powder or another offered form. | Confirm compatibility with the intended formulation before comparing price. |
Keep typical values and contractual limits in separate columns. A typical figure describes the product; an agreed acceptance limit defines what happens when a delivery is assessed. Record units explicitly, especially for oil absorption, because datasheets do not always use the same convention.
Can GCC replace titanium dioxide?
There is no universal replacement ratio. Calcium carbonate and titanium dioxide have different functions. Certain mineral selections and formulation adjustments can support more efficient pigment use, but the result must be demonstrated through coating tests. A lower-cost wet formulation is not a saving if more coats are needed to reach the required coverage.
Ask the formulator to compare the agreed opacity or contrast-ratio result at controlled application thickness, together with gloss and durability requirements. Do not approve a substitution from the powder’s whiteness alone.
How to organise a useful grade trial
- Keep a reference. Retain the current approved paint and its formulation, raw-material lots and test results.
- Define the first comparison. Record the proposed filler substitution and hold other changes to a minimum. If the formulation is adjusted, document those changes separately.
- Record preparation. Note addition order, mixing equipment, dispersion conditions and the point at which viscosity is measured.
- Test the finished film. Select the relevant appearance and performance checks before the trial, including the conditioning and measurement procedure.
- Review production practicality. Include handling, packaging, cleaning and the results of any storage-stability check, rather than judging only the first laboratory drawdown.
For repeat trials, use the same worksheet and identify every sample by supplier grade and batch. That makes a later difference traceable instead of leaving the team to compare photographs or informal descriptions.
What should you send with an enquiry?
Provide the paint type, current filler specification, target finish, key acceptance tests, expected quantity, packaging and destination. Include the present grade or an anonymised reference specification if commercial confidentiality matters. State whether you need a laboratory sample, technical documents or a commercial quotation.
Review Carbocore’s calcium carbonate range, explore paint and coating applications, or use the technical resources section before sending a technical enquiry.
Is the finest grade always the right choice?
No. Select the grade against the complete specification and production trial. Finer material should have a defined purpose in the formulation; it is not a substitute for matching the required surface finish, processing behaviour and cost.
Technical references
These references describe general material behaviour. Specifications and acceptance criteria must relate to the proposed grade and its intended use.
