Though hydrophobic coatings offer several performance benefits, to mimic the self-cleaning capabilities of the lotus leaf, the coatings must be super-hydrophobic, as not all hydrophobic coatings are super-hydrophobic.
The benefits of super-hydrophobicity
Super-hydrophobic materials possess a highly water-repellent surface, similar to a lotus leaf. Their microstructure mimics the lotus plant to minimize the contact areas for water and dirt.
Measuring the hydrophobicity of a material requires looking at the contact angle by placing a water droplet on the material’s surface. The advancing angle just as the droplet starts to move is the contact angle.
The higher the contact angle, the higher the hydrophobicity. Higher hydrophobic materials will have less water on the surface and dry faster, leading to improved performance in critical factors, affecting the performance of the building’s exterior. This includes better freeze-thaw resistance, mildew and weathering resistance, UV protection, dirt collection capabilities, and staining resistance.
No matter which facade solution is selected, whether above-grade concrete, concrete masonry, exterior insulation and finish systems (EIFS), stucco, or previously painted wall surfaces, a coating or finish will be applied for added protection and esthetics. A hydrophobic coating offers additional armour and long-term value. With these applications in mind, super-hydrophobic coatings can help to enhance building performance in the following ways:
Durability
Coatings with rapid drying and water-shedding properties reduce maintenance costs and facility downtime. Enhanced water shedding products could last 10 years, compared to the average of two to three years for traditional coatings. This reduces the need for recoating, saving maintenance costs and improving operational efficiency.
Enhanced water shedding products can maintain their original clean appearance for seven to 10 years, compared to two to three years for traditional architectural coatings without water-shedding properties.
Traditional coatings can typically offer substrate protection beyond two to three years; however, they are limited in their ability to stay clean and offer enhanced fade resistance. For lighter colours (e.g. lightness values greater than 55) traditional architectural coatings start to experience noticeable dirt, fungal, algal growth and can give potential customers a poor impression of the business. Fade resistance is also another key property of coatings. Enhanced water-shedding products are typically formulated with silicone polymer additives, which provides longer durability than traditional acrylic coatings.
Safety and appearance retention
Hydrophobic coatings better resist mould, mildew, and algae growth and exhibit UV-stability and excellent weather resistance. This translates to a better long-term appearance, and an improved exterior which will not break down via long-term exposure to the elements.
Extended building lifecycle
Super-hydrophobic coatings provide reliable facade systems, materials, and assemblies, with more durable formulas and reduce the total cost of ownership. Over a two-decade installation, the super-hydrophobic coating has the potential to save almost 80 per cent in total cost of ownership over a standard coating product.
Some building owners have reported that with traditional coatings, they needed to pressure wash every one to three years. After recoating with s hydrophobic coating or finish, they have extended the time frame to five to seven years. This would be dependent on climate condition and geographic location.
The elimination of yearly pressure washing and the result of improved durability provide long-term savings over traditional architectural coatings (e.g. latex). Referring back to traditional coatings under the durability section of this article, the same properties contribute to extending a building’s lifecycle.
It must be noted, not all super-hydrophobic and hydrophobic coatings/finishes are created equal, which is why it is important to review product bulletins and data sheets. Performance properties, such as mould resistance, salt spray, freeze-thaw resistance, accelerated weathering, and water vapour permeability, are tested and commonly published. This criterion typically follows ASTM test methods or other industries standard testing procedures and is an indicator of performance and durability. One testing criteria critical to the performance of these products, but is often overlooked and seldomly published on data sheets, is the contact angle of super-hydrophobic compared to hydrophobic products.
Boosting cleanliness
Hydrophobic and super-hydrophobic technologies create low surface energy and non-polar structures. As previously mentioned, super-hydrophobic coatings have self-cleaning properties, and hydrophobic coatings are fast drying, and offer enhanced mould, algae, and mildew protection.
