The components of paints and coatings can be divided into polymers, pigments, solvents and additives.  The most common polymers used are generally low gloss polyester, acrylic, epoxy, polyurethane, vinyl or alkyd types.  Pigments are usually white or coloured mineral oxides.  Extender pigments, including kaolin, also act as fillers in paints as well as pigments.  Solvents act as carriers for the other components and react with them during the paint drying/hardening process.  Additives are used to accelerate or retard drying, prevent the growth of fungus and other forms of life within paint, suspend pigments in the paint and also to wet the surface to which the paint is being applied.

Calcined kaolin is most commonly used in paints.  This is a more valuable form compared to other types of kaolin.  The paint industry is relatively more important than its consumption of kaolin would suggest.

The three main reasons for using kaolin in paint are as follows:

Reduce unit consumption of expensive pigments, such as titanium dioxide (TiO₂)

Add desired rheological properties to the paint film to maintain dispersion and provide body to the product.

Improve the processing, storage and application properties of the paint film

Other extender and filler pigments used in paint include fine ground calcium carbonate and micronised talc.  The extremely wide varieties of paint formulations mean that other minerals are also used in certain specialist applications.  Barytes, bentonite, precipitated calcium carbonate (PCC) and mica can be used in exterior and corrosion resistant paints.  

The use of a particular mineral used as a pigment and extender in a paint formulation depends on the physical properties of the mineral.  These include brightness, particle size and shape, dispersibility, oil absorption, viscosity and resistance to chemicals, heat and moisture.  The most important of these properties are summarised below:

Brightness

Oil adsorption (controls the filler loading)

Particle size distribution (controls packing density, abrasion resistance and spreading characteristics of the paint)

Viscosity (controls the thixotropy, stability and settling resistance of the paint)

The main application for kaolin in paint is in architectural paint, especially non-gloss interior wall products.  Kaolin is also used in paint undercoats as a suspending agent for heavy extending minerals such as barytes.  The incorporation of kaolin in a paint formulation tends to result in a paint that is less durable than one formulated with other minerals.  This effect limits the use of kaolin in exterior paints where the main filler minerals are talc and calcium carbonate.  Kaolin is suitable for use in emulsion paint because its hydrophilic characteristic makes it easily wetted by water.  A further advantage of kaolin in paint is that it can be produced with the same particle size as titanium dioxide, which makes precise paint formulations easier to manufacture.