Silicate mineral paint, or mineral paint, is a coating that uses mineral binders. Two related mineral binders are used in coatings: lime and silicate. Under the action of carbon dioxide, lime-based binders carbonate, while silicate-based binders set, and together they form hydrated calcium silicate.
Lime paints, apart from fresco technique, have only moderate weather resistance and are therefore used mainly in heritage conservation. Mineral paint usually means silicate paint. These paints use potassium water glass as binder and are also called water-glass paints or Keimfarben, after their inventor.
Mineral silicate coatings are considered durable and weather-resistant, with a service life that can exceed one hundred years. The town hall of Schwyz in Switzerland and the White Eagle Inn at Stein am Rhein were painted with mineral coatings in 1891, exterior walls in Oslo, Norway, in 1895, and exterior walls in Traunstein, Germany, in 1891. These historic cases show that silicate paints can remain stable through long climatic exposure when correctly applied.
Alchemists seeking the philosopher's stone and the manufacture of gold found shiny glassy beads in their fireplaces. Sand mixed with plant ash and heated condensed into water-glass beads. In the 19th century, Van Baerle at Gernsheim and Johann Gottfried Dingler at Augsburg first produced industrial water-glass discs for use as window panes. Johann Nepomuk von Fuchs first tried to make paint from water glass.
Around 1850, the painters Kaulbach and Schlotthauer applied exterior paint to the Munich painting gallery. Because they used earthy pigments that could not be silicified, the pigment washed out of the water glass. This failure showed that silicate paints must use alkali-resistant mineral pigments that chemically bond with water glass rather than ordinary earth pigments.
In 1878 the craftsman and researcher Adolf Wilhelm Keim patented mineral paint. Since then the paints have been made by the successor company Keimfarben at Diedorf near Augsburg. Keim relied on V. van Baerle as a source of water glass and also tried to make silicate paint himself. His experiments matured over many years and eventually gave good results. Silinwerk van Baerle at Gernsheim on the Rhine and Keimfarben at Diedorf near Augsburg are both well-known manufacturers.
Keim's motivation came from King Ludwig I of Bavaria. The art-loving monarch was impressed by the colourful lime frescoes of northern Italy and wanted similar works in his kingdom. However, the harsher weather north of the Alps destroyed the paintings within a short time. He therefore ordered Bavarian scientists to develop a paint with the appearance of lime but greater durability.
Mineral paint contains inorganic pigments and an alkaline potassium-based silicate, water glass, also called potassium silicate, liquid potassium silicate or LIQVOR SILICIVM. Mineral paint does not form a separate layer but bonds permanently to the substrate in a process called silicification.
This produces a highly durable bond between coating and substrate. The water-glass binder is highly resistant to ultraviolet radiation. While acrylate- or silicone-based paints become brittle, chalky and cracked under ultraviolet exposure over the years, the inorganic water-glass binder remains stable. Chemical fusion with the substrate and the ultraviolet resistance of the binder are the fundamental reasons for the very long service life of silicate paints.
Silicate paints require a silica-containing substrate to set and are therefore well suited to mineral substrates such as mineral plaster and concrete, with limited use on wood and metal. The water-vapour permeability of silicate paint equals that of the substrate, so it does not impede vapour diffusion. Moisture in the building structure or plaster can diffuse outward freely, keeping walls dry and preventing structural damage. This helps avoid condensation at the surface and reduces the risk of algae and mould.
The high alkalinity of the water-glass binder enhances its resistance to microbial growth and avoids the need for additional preservatives. Because mineral coatings do not build static charge or become thermoplastic like dispersion or silicone coatings, dirt adheres less and attached particles are easier to clean. Silicate paints are non-combustible and contain no organic additives or solvents, in accordance with DIN 18363, section 2.4.1.
Silicate paints have high colour stability. Because only mineral pigments that do not fade under ultraviolet radiation are used, colours can remain unchanged for decades. Silicate paints are based on mineral raw materials and are environmentally compatible in manufacture and use. Their durability conserves resources, and their pollutant-free composition benefits health and the environment, making them increasingly popular in sustainable construction.
Three types of silicate paint are usually distinguished. Pure silicate paint consists of two components, a pigment in dry or slurry form and liquid water-glass binder, according to DIN 18363 section 2.4.1. Processing pure silicate paint requires experience and expertise and is now regarded as a historic technique.
Around the middle of the 20th century the first one-component silicate paints appeared. Adding no more than 5% by mass of organic additives such as acrylate dispersion, water repellent, thickener or similar substances allowed ready-to-use paint to be sold in cans. These are called dispersion silicate paints, according to DIN 18363 section 2.4.1. Their application range is much wider than that of pure silicate paint because the dispersion allows use on substrates that are not sufficiently strong or that contain organic components. Handling and application are also simpler than for pure silicate paint.
In 2002 a third type was introduced: sol-silicate paint. Its binder is a combination of silica sol and water glass. The organic fraction is limited to 5% by mass, similar to dispersion silicate paint, allowing chemical setting while retaining the specific advantages of silicate. Sol-silicate paint can be used on non-mineral plaster. For this type, bonding occurs both chemically and physically. Sol-silicate paints have transformed the application range of silicate paints and can be applied easily and safely to almost all common substrates.
Silicate paints are suitable for concrete, gypsum plaster, lime plaster, masonry and stone. The substrate must be clean, sound and of suitable absorptivity and must be able to react with the alkaline water glass. Loose, chalky or organic-containing old coatings must be consolidated or removed, otherwise silicification cannot form an adequate bond.
Silicate paints are used for environmentally friendly, non-toxic applications, especially on masonry products, and offer high durability and light fastness. Their high water-vapour permeability keeps walls dry and reduces condensation and mould, acid-rain resistance suits industrial environments and historic buildings, antifungal properties reduce maintenance, and on cement-based materials silicate paint can reduce carbonation and protect reinforcement from corrosion.
In historic building restoration, silicate paints are widely used because they are breathable, weather-resistant and colour-stable. In new construction they are used on facades, basements, garages and damp areas. Product instructions and DIN standards should be followed, with control of dilution, application temperature and drying conditions to ensure adequate silicification.