Lesson 14. SiliconesIn this lesson you will get acquainted with a very interesting type of binder, which differs from the standard polymer options we studied earlier. You will learn about the features of silicones and examine their influence on environmental factors that determine their areas of application.
Silicones are a hybrid that has taken the best of both worlds: durability and vapor permeability of mineral systems, and elasticity and water resistance of polymers.
The secret of their unique properties lies in their chemical structure. Unlike acrylics, the backbone of the silicone polymer chain is not carbon, but silicon and oxygen, similar to natural quartz. This gives the binder excellent resistance to UV radiation and temperature fluctuations.
The process of creating silicone binder is unique and differs from acrylic production. Unlike acrylic and other polymers we studied (which are petroleum‑based), silicone production begins with quartz sand. Through complex processing, pure silicon is obtained.
At the chemical plant, silicon and other components are used to create a special “hybrid brick” — the siloxane molecule. Its “skeleton” consists of strong silicon‑oxygen bonds, like stone or glass, while the side “tails” are organic groups, like polymers.
When mixed in water, unlike acrylic, ready molecules or short chains of siloxane are mechanically introduced into water with emulsifiers. This makes the process simpler in design but more expensive in cost, since the initial silicone components are technologically more complex and costly.
The result is a silicone dispersion — water containing microscopic droplets of ready silicone resin. When applied to a wall, the water evaporates, chains assemble, and form the “breathable membrane” with water‑repellent properties.
Main properties and advantages:- Highest vapor permeability: Comparable to mineral systems.
- Excellent water repellency: Active protection against wetting.
- High resistance to UV radiation and weathering: Coating does not fade or degrade for decades.
- Elasticity: Sufficient to bridge microcracks.
- Dirt resistance: Hydrophobic surface soils less and has self‑cleaning ability during rain.
The only significant limitation of silicone binders is their high cost. They are not mass‑market products but specialized solutions for the most demanding projects, where durability and proper functioning of the entire facade system are paramount.
When you see labels like “water‑dispersion,” “water‑based,” or “emulsion paint” on packaging, in most cases this means the binder is polymeric or copolymeric. It may be acrylic, styrene‑acrylic, butadiene‑styrene, vinyl acetate, or vinyl acetate‑ethylene dispersion. These materials form the basis of the modern market thanks to their versatility, ease of use, and reasonable cost.
Silicone water dispersions, although possessing outstanding properties — high vapor permeability, UV and moisture resistance — are most often used in facade systems. Indoors they are used less frequently, mainly due to higher cost. Moreover, for optimal balance of price and performance, manufacturers often do not use pure silicone resin but create combined binders — for example, silicone‑acrylic or silicone‑styrene‑acrylic. These compositions combine the best properties of their components and provide a balanced result.
In any case, all these materials belong to one general category — water‑dispersion binders. This is a large and very diverse group, including both high‑quality premium solutions and more affordable options.
Before moving on to the next binder, which stands at the boundary between film‑forming water dispersions and reaction‑curing systems, let’s analyze how the water‑dispersion binders we have studied interact with operational and aesthetic limiting factors. This will determine how well the material suits a specific task and operating conditions.
Influence on operational factors (interaction with moisture):- Water resistance (direct water exposure): Very high. This is the key property of silicone resins. Thanks to organic groups on the polymer chain surface, the coating acquires a pronounced hydrophobic effect. Water droplets cannot wet the surface; they bead up and roll off without penetrating. This phenomenon is called the “lotus effect.”
- Moisture resistance: Very high. The mineral “skeleton” of the binder is absolutely inert and chemically stable. It does not absorb water vapor, soften, or lose adhesion even at 100% humidity, making it ideal for any climate.
- Vapor permeability: Very high. This is the second unique feature of silicone. Although it repels liquid water, its molecular structure has sufficiently large micropores. These pores are too small for water droplets but large enough to allow water vapor molecules to pass freely. This combination makes silicone coatings the best “breathable membrane” for facades.
- Wet abrasion resistance: High. Silicone film combines elasticity and low friction. The surface is smooth and “slippery,” reducing wear during cleaning. Hydrophobic properties also prevent water from softening the coating, resulting in high resistance to wet cleaning.
- Resistance to biological damage: High. Protection against mold and fungus is twofold: the hydrophobic surface remains dry, preventing microorganism growth, and the organosilicon base is not a nutrient medium.
Interaction with mechanical impact:- Resistance to abrasion and scratches: Medium. Silicone film is not very hard; it is more elastically resilient. Its scratch resistance is lower than quality acrylic.
- Impact resistance: High. Elastic structure absorbs impact energy well, protecting the coating from chipping.
- Elasticity and crack resistance: High. Silicone resins form a very flexible film capable of bridging microcracks and adapting to substrate thermal expansion, which is critical for facades.
Other specific operational factors:- UV resistance: Very high. The mineral silicon‑oxygen backbone is absolutely inert to solar radiation, like stone or glass.
- Heat resistance: High. Silicone resins withstand much higher temperatures than acrylics without softening. Decorative coatings based on silicone resins can withstand 120–150 °C or more, depending on composition and additional heat‑resistant components.
- Frost resistance: Very high. Retains elasticity even in severe frost, and combined with hydrophobicity, makes it ideal for harsh climates. During storage and transport, silicone dispersions withstand several freeze‑thaw cycles without losing properties after thawing. This is a key difference from most other water‑based compositions (especially vinyl acetate).
- Environmental safety in use: High. Once dry, the coating is completely safe. The material contains no harmful solvents.
Influence on aesthetic factors:- Color (tinting possibilities): High, but with limitations. Silicone resins are transparent and have neutral pH, allowing a wide range of pigments, including pure colors. They do not have restrictions typical of alkaline mineral binders. However, since they are mainly used in facade systems, only highly durable inorganic pigments are used for tinting, ensuring no fading under UV. The palette is bright but limited to shades achievable with inorganic pigments.
- Texture and relief: Medium variability. Silicone binders are mainly used for thin‑layer and medium‑layer facade paints and plasters (“bark beetle,” “lamb”). They hold heavy filler well, but their main task is protective, not shaping.
- Degree of gloss: Deep matte. Silicone coatings always form a deep matte surface. Their structure does not allow gloss, since for effective “breathable membrane” function the surface must remain microporous. Gloss effects are achieved only by applying finishing varnishes, which may reduce vapor permeability.
- Optical effects: None. The aesthetics of silicone coatings are based on uniformity, depth of color, and naturalness. They do not create complex optical effects, iridescence, or inner glow. Their visual value lies in monumental, pure color and excellent durability of texture.
All these water‑dispersion binders have become the foundation of the modern decorative and paint materials market. Their popularity is explained by convenience of use, environmental safety, and wide variability of properties. This group forms the technological basis of 95% of all modern interior and facade paints and decorative plasters. Understanding the principles and capabilities of water dispersions allows conscious material selection, avoiding marketing traps, and achieving high results in work.
