Lesson 8. Silicate Binder

In the previous lesson, we examined cement binder — the champion of strength and water resistance, but with a drawback in vapor permeability. Today we move on to the last participant in the mineral binder group — silicate binder. You will learn its features and how it influences operational and aesthetic factors.

What is Silicate Binder?

Silicate binders are aqueous solutions of potassium silicates, widely known as “liquid potassium glass.” In the hierarchy of mineral binders, they occupy a special place, serving as a high‑tech solution that combines the durability of stone with the penetrating ability of liquid.

Their hardening process is dual: first, water evaporates from the material, and then liquid glass reacts chemically with carbon dioxide from the air and, most importantly, with minerals (fillers) in the substrate (such as quartz). This process is called silicatization or petrification. As a result, the coating does not simply adhere to the surface but chemically fuses with it, forming a single, extremely strong and vapor‑permeable monolith. This unique hardening mechanism defines both the advantages and strict limitations of silicate materials.

Influence on Operational Factors

Interaction with moisture

• Water resistance: High. This property is a direct consequence of silicatization. Liquid glass reacts with the mineral substrate to form a chemically stable, water‑insoluble silica structure that becomes one with the surface rather than a film on top. The coating acquires a hydrophobic effect: water droplets bead and roll off without penetrating.
• Moisture resistance: Very high. The hardened mineral structure, similar to quartz, contains no hygroscopic or water‑sensitive components. Unlike gypsum, it does not absorb moisture from the air or lose strength, making it suitable even for the most humid conditions.
• Vapor permeability: Like lime, silicate coatings have a microporous structure that allows vapor to pass freely. Their vapor permeability is comparable to lime plasters. This unique combination of high water resistance and high vapor permeability is the main advantage of silicate systems for facades.
• Wet abrasion resistance: High. The coating is very hard and durable, resistant to washing and cleaning. Its strength comes from being a monolithic structure chemically fused with the substrate, not a thin paint film.
• Resistance to biological damage: High. Like lime, liquid glass creates a strongly alkaline environment (high pH), acting as a natural antiseptic that prevents mold and fungi. This protection is permanent, inherent to the material itself, unlike temporary biocidal additives in acrylics.

Interaction with mechanical impact

• Abrasion and scratch resistance: Very high. Due to chemical bonding with the substrate and inherent hardness, silicate coatings have excellent resistance to abrasion, making them ideal for high‑load surfaces such as building bases, ground floors, and public spaces.
• Impact resistance: High. Silicate coatings are strong and hard, resistant to most everyday loads. However, like all mineral systems, they lack plasticity — under sharp localized impact they are more likely to chip than dent, unlike elastic polymer coatings.
• Elasticity and crack resistance: Low. Silicate binder forms a strong but rigid structure that cannot compensate for substrate movement or microcracks. Unlike polymers, it does not stretch or relieve stress. Thus, silicate coatings require stable, reinforced substrates without movement or settlement, otherwise cracking may occur.

Other specific operational factors

• UV resistance: Very high. Silicate binders are fully mineral and unaffected by ultraviolet radiation. They do not fade, lose strength, or degrade under sunlight, making them ideal for facades and interiors with strong natural light. Pigments, however, may vary in lightfastness.
• Heat resistance: Very high. Silicate binders are non‑combustible and originally products of high‑temperature synthesis, which ensures stability under heat. They do not soften, lose strength, or emit harmful substances. They are excellent for surfaces exposed to heat — fireplaces, chimneys, radiators — provided other components (pigments, additives) can withstand the temperature.
• Frost resistance: High. With strong, dense, inorganic structure, silicate coatings resist repeated freeze‑thaw cycles. They do not absorb critical moisture, crack, or lose adhesion at low temperatures, making them suitable for facades in harsh climates.
• Storage and transport: Supplied ready‑to‑use in liquid or paste form, silicate materials require special care. They exist in an alkaline aqueous medium (liquid potassium glass), making them sensitive to freezing. Once frozen, they irreversibly lose properties. Therefore, they must be stored and transported only at positive temperatures, avoiding even brief freezing.
• Environmental safety: High. In hardened form, silicate materials are clean and safe. In liquid form, however, liquid glass is a strong alkali requiring strict safety measures and personal protective equipment during application.

Influence on Aesthetic Factors

• Color and tinting: Limited. As with lime, high alkalinity restricts tinting. Liquid potassium glass (pH 11–12) is chemically aggressive, destroying most bright organic pigments, causing fading or unpredictable tone changes. Only inorganic alkali‑resistant pigments should be used.
• Texture and relief: Moderate variability. Silicate binders are mainly used in thin‑layer or medium‑layer decorative plasters and paints, where texture depends on fillers, tools, and application technique.
• Gloss level: Deep matte. Silicate coatings do not form a film on the surface and always have a natural, deep matte finish without gloss. Polishing only wears the surface, not creating shine.
• Optical effects: None. They create smooth, uniform, “calm” coatings. The aesthetic of silicate materials lies in naturalness and monumentality, not decorative effects.

Conclusion

We have now examined all four main types of mineral binders: lime, gypsum, cement, and silicates. Despite their differences, they share a common philosophy — materials that, during hardening, strive to return to their natural, stone‑like state.

Strengths of mineral binders:

• Durability and UV resistance
• Vapor permeability (except dense cement), allowing walls to “breathe”
• Natural, noble aesthetics of matte surfaces
• Environmental safety and non‑combustibility

Weakness: low elasticity. Being essentially stone, they cannot stretch or compensate for substrate deformation. This limitation drove the chemical industry to create a fundamentally different class of materials — polymer binders.

Clay, despite its natural origin and historical use, was not included in detail here because it is rarely present in modern decorative plaster systems and commercial products. It is mainly used in ecological construction, manual restoration, or niche artistic projects. Our course focuses on binders actively used in professional decorative practice.

Unlike mineral binders that harden through chemical reactions, polymers work differently — they form a strong, elastic film on the surface after the solvent (usually water) evaporates. This mechanism solved the main problem of mineral systems — their brittleness.

Having completed the study of mineral binders, we now move on to the second group — synthetic or polymer binders.