SMI: Ground Calcium Carbonate (GCC) in Paint

Specialty Minerals Ground Calcium Carbonate for Paint and Coatings

Ground calcium carbonate (GCC)—also called ground limestone, whiting, or chalk—is the most widely used extender mineral in coatings applications. It is available worldwide and close to most paint manufacturing locations. It is very bright and comes in a wide range of particle size distributions. Finally, it is the most economical of all common filler minerals.

The widest use for GCC is as a filler in architectural or decorative coatings. While it is primarily used in interior paints, it is included in some exterior formulations as well. It tends to be the filler of choice for paints sold at a low price point and/or where longevity is not the primary attribute. That said, GCC is also used in top-of-the-line flat or matte finishes.

High-brightness calcium carbonates are selected for ceiling paints and other applications requiring high dry hiding and are formulated above the critical pigment volume concentration (CPVC). By combining two or more grades of different particle sizes, thus altering the particle size distribution of the filler package, manufacturers can adjust the flatness of finish of interior architectural coatings and improve the scrubability of the final paint film. GCC can be used in exterior building paints as long as the pigment volume concentration (PVC) is not too high. The PVC must be sufficiently low with enough binder present so that the film does not become too porous over time.

GCCs are also economical extenders included in road-marking and traffic-paint formulations to lower costs while still meeting the optical specifications for the finished film.

Although GCCs have many desirable traits, it is not a universal extender mineral. It will react with acids, so its use it limited to areas where it will not be exposed to acid rain or other acidic fumes or liquids. In contrast to high-aspect ratio platy talcs, calcium carbonates, with their round or nodular particle shape and low aspect ratio, make relatively little contribution to improved film formation and integrity and will increase film porosity. For these reasons, the use of GCCs are limited in industrial, marine, and metal-protective maintenance coatings.

Ground Calcium Carbonates from Specialty Minerals
GCCs are mined and processed in the U.S. at Specialty Minerals Inc. locations in Adams, Massachusetts and Lucerne Valley, California. Key products for the paint and coating industry are:

Vicron^® - East and Vicron^® – West GCCs are a series of high brightness GCCs with particle sizes from 2 to 13 microns which produce paint fineness of grinds from 6 to 3 Hegman.
Marblewhite^® - East and Marblewhite^® - West GCCs are bright ground limestones which are slightly coarser at 325 and 200 mesh yet useful in flat or heavily bodied coatings.

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