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What Makes Silicone Render Hydrophobic?

In the world of construction and building materials, the term “hydrophobic” often piques the interest of architects, builders, and homeowners alike. A hydrophobic surface repels water, making it invaluable in wet or damp conditions. Silicone render is one such material that boasts hydrophobic properties, but what exactly makes it capable of fending off water?

The science

Silicone is a synthetic material made up of silicon, oxygen, carbon, and hydrogen. Unlike its organic counterpart, silicon (a natural element found in sand and rocks), silicone is far more versatile and resilient. The molecular structure of silicone features a chain of alternating silicon and oxygen atoms, surrounded by organic groups. These organic groups make silicone hydrophobic.

How hydrophobicity works

A material is considered hydrophobic if it has a contact angle of more than 90 degrees with water. In simpler terms, water droplets will form beads rather than spreading out on a hydrophobic surface. The molecular structure of silicone lends itself to this characteristic by creating a surface that repels water molecules. The result? A surface where water droplets bead up and roll off rather than permeating the material. The phenomenon is often referred to as the lotus effect. Picture a lotus leaf; water droplets will form and pool, then proceed to slide towards the centre of the large circular leaf. Silicone Render’s surface mimics this. However, in the instance of a rendered wall, the droplets slide off and grab dirt along the way. As such, silicone render also becomes self-cleaning.

Additional additives

While the inherent structure of silicone contributes to its hydrophobicity, additional water-repellent additives can further enhance this quality. These additives can create a surface that not only repels water but is also resistant to algae and fungi, which thrive in damp conditions.

Silicone render acquires its hydrophobic characteristics through a combination of its inherent molecular structure and additional enhancements made during the manufacturing process:

  1. Inherent molecular structure:
    • Silicone polymers have hydrophobic properties owing to their molecular structure. The sidechains in silicone polymers make them hydrophobic, meaning they repel water. These sidechains most commonly consist of methyl groups, which also hinder silicone’s reactivity with other chemicals and prevent it from adhering to many surfaces.
  2. Silicone emulsion:
    • Silicone render is composed of silicone emulsion and, in some cases, potassium crystals. The silicone emulsion contributes to the hydrophobic quality of the render, making it highly resistant to water and dirt, which also lends the render self-cleaning properties.
  3. Nano-particle technology:
    • In some advanced silicone render products, nano-particle technology is employed to enhance the hydrophobic quality of the render. This technology amplifies the water-repelling properties of the render, ensuring long-lasting protection against moisture and other environmental factors.


Enhanced durability
  1. Weather Resistance: Silicone render’s hydrophobic nature grants it an extraordinary resistance to the vagaries of weather, be it rain, sleet, or snow. This means that over the years, the rendered surface will display minimal signs of weather-related wear and tear.
  2. Structural Integrity: By repelling water, hydrophobic silicone render reduces the risk of water infiltrating the underlying structure. Water infiltration can cause a host of problems, from structural weakening to increased susceptibility to frost damage.
Aesthetic longevity
  1. Colour Stability: Hydrophobic properties help to keep the pigments in the render stable, reducing fading and discolouration that can occur over time, especially in areas exposed to high levels of UV radiation.
  2. Uniform Appearance: The water-repellent surface minimises the ‘streaky’ look that can result from water stains or algae and fungal growth, thereby maintaining a uniform appearance.
Improved insulation
  1. Energy Efficiency: When walls are damp, their thermal conductivity can increase, making the building less energy-efficient. Hydrophobic silicone render helps keep the wall dry, thereby maintaining the wall’s insulating properties and potentially lowering energy bills.
  2. Condensation Control: The water-repellent nature also minimises the risk of condensation within the walls, which can lead to dampness, mould growth, and further insulation issues.
Ease of maintenance
  1. Reduced Cleaning Requirements: A hydrophobic surface is more difficult for dirt and grime to cling to. This means cleaning intervals can be extended, saving both time and money in the long term.
  2. Cost-Effectiveness: While the initial investment may be higher than traditional renders, the reduced need for repair and maintenance makes hydrophobic silicone render a cost-effective solution in the long run.
  3. Antimicrobial Properties: Some hydrophobic silicone renders are formulated with additional antimicrobial agents. This makes the surface not just resistant to water but also inhospitable to mould, mildew, and other microbial contaminants.
Versatility in applications
  1. Multiple Environments: Its resistance to water and biological growth makes silicone render suitable for a variety of environments, from high-moisture areas like bathrooms and kitchens to external facades exposed to harsh weather conditions.
  2. Adaptable Surface Treatment: The hydrophobic properties can be integrated into various finishes, from a smooth, modern look to a more traditional, textured appearance.
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