Mineral and Silicate Coatings

About this course.

Mineral silicate coatings are paints whose binder is an inorganic mineral compound — most commonly potassium silicate, historically called "water glass" — rather than the organic resin used in ordinary paint, and they differ fundamentally because they chemically react with a mineral substrate and bond into it, through a process called silicification, becoming part of the surface, whereas an ordinary paint dries to form a separate film that merely sits on top and adheres mechanically. This one difference — a chemical bond into the surface versus a film on the surface — is the source of almost every distinctive property of silicate coatings, so understanding it is the foundation of the whole course.

How ordinary film-forming paint works. A conventional paint (whether water-based acrylic or solvent-based) consists of a binder (an organic resin such as acrylic), pigments, a carrier (water or solvent) and additives. When it is applied, the carrier leaves and the resin particles coalesce into a continuous film that lies on top of the substrate. The film sticks by adhesion — a mechanical and physical grip on the surface — and it is essentially a thin layer of plastic-like material bonded to, but distinct from, the wall beneath. Because it is a discrete film, it can in principle peel, flake, blister or lift if adhesion fails, if moisture gets behind it, or as it ages and becomes brittle. It also, to varying degrees, forms a barrier that can restrict the movement of water vapour through the surface.