Architectural coatings are used on the interior and exterior of structures such as houses, apartments and office buildings. Other terms for architectural coatings are trade-sales paints, decorative coatings, building paints, and DIY (do it yourself) paints. Included are the semi-transparent and opaque stains for wood. These are the coatings people most commonly see, use, and apply.
To satisfy the decorative and functional needs of their users, paints for home and commercial construction are formulated in a wide range of appearances, from flat or matte to shiny high-gloss with ranges of eggshell and semi-gloss in between. Exterior architectural coatings and wood stains must be formulated to withstand the rigors of wind, rain, and direct sunlight. Interior paints are generally used in a more benign environment, but one where surface flaws are more readily noticed, and where touch-up and washability are important.
The color of the coating is determined by the prime pigment used. This will usually be titanium dioxide (TiO2), if the paint is white or light-colored; in darker paint shades, it may be iron oxide, carbon black or some brightly colored organic pigment.
Extender and Filler Minerals in Architectural Paints
In addition to the prime color pigments described above, decorative coatings and stains also contain filler or extender pigments, such as ground calcium carbonate (GCC), talc, kaolin, silica, and barytes. The key function of these minerals is to lower costs by either extending or maximizing the efficiency of the more costly color pigments, reducing the amounts needed to achieve the desired color, and filling up the volume in the paint, thus reducing the use of resins and/or solvents.
In choosing a filler pigment, both the demands of the end use and the cost constraints (i.e. selling price) must be considered. The performance of a given filler in a coating depends on its basic chemical nature, as well as its particle size, particle shape, surface chemistry, color, and whiteness or brightness (both dry and wet). Most decorative coatings contain a combination of filler minerals of different types and sizes to achieve the targeted balance of application, appearance, durability, and cost properties.
Ground calcium carbonates, also called ground limestones, are generally the most economical and are very bright. However, they do not contribute much to film integrity and their chemistry makes them subject to acid attack. The synthetic form of calcium carbonate, precipitated calcium carbonate (PCC), is widely used in some areas of the world, especially in latex or emulsion paints.
Talc improves moisture barrier properties of exterior paints and semi-transparent or opaque stains due to its platy particle shape and hydrophobic nature. It is not as bright as the best calcium carbonates and is higher in cost. Talc is also used in predispersed liquid colorants for point-of-purchase paint-tinting systems where it aids suspension and color development of the prime color pigments in the colorant.
Barytes, also called barite, sits on the high end of the scale in chemical inertness and specific gravity and can also be very bright. This makes it a good pigment for primers—but also drives up the weight, and therefore the cost, of a gallon or liter of paint.
Specialty Minerals Filler and Extender Pigments for Architectural Coatings
In the U.S. Specialty Minerals Inc. (SMI) manufactures a variety of filler pigments used in trade sales paints. These include:
- Vicron® - East and Vicron® - West GCCs – high-brightness fillers, from 3 to 13 microns, from SMI mines and plants in Adams, Massachusetts and Lucerne Valley, California.
- Marblewhite® - East and Marblewhite® - West GCCs – 125, 200 and 325 mesh bright limestones, also manufactured in Adams, Massachusetts and Lucerne Valley, California.
- Talcron® talcs – 1 to 8 micron bright paint talcs, mined and manufactured in Barretts, Montana.
- BaricronTM barites – bright white barytes, 1.5 to 8 microns, made from Chinese ores.
Grades of PCCs for paint include:
- Calopake® F PCC – 2 micron clustered scalenohedral calcite PCC for exceptional brightness and titanium dioxide extension. Manufactured in SMI’s Birmingham, U.K. facility.
- SturcalTM F PCC – 2.8 micron acicular aragonite, also produced in Birmingham.
- RevestCarbTM PCC – 1.9 micron scalenohedral calcite, manufactured in SMI’s plant in Jacarei, Brazil.
Click on a product name to download the data sheet for that product.
Or follow one of these links for more information on an SMI paint filler type:
- Barytes in coatings
- Ground calcium carbonates in coatings
- Precipitated calcium carbonates in coatings
- Talcs in coatings
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