Hydrophobic coatings unlock protection against water intrusion

by arslan_ahmed | December 9, 2022 5:13 pm

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By James Howell

Water intrusion causes significant problems for buildings and can go as far as damaging the structure. The building products industry is continuously looking for new technologies to assist with the prevention of water damage. Nature, as a notorious problem solver, often inspires solutions within the industry.

Complete prevention of water intrusion is important for buildings. Much of the surface area of buildings are covered by paint and coatings, which are made to withstand the punishment of extreme weather, therefore new technology is very much needed in this category. Hydrophobic coatings are using new technology to repel water with acrylic coatings. This type of coating was inspired by the waterproof properties of the lotus flower.

The lotus flower is native to Southern Asia and Australia, and it roots itself in the mud and stretches up to the top of the water, producing lush blossoms. As it rises from the mud without stains, lotus often symbolizes purity. Since it blooms at the break of the day and returns to the water each evening, the flower is also known to signify strength and resilience.

The leaves of the lotus plant are coated in a wax, which helps keep the plant waterproof and clean. The leaf’s microstructure consists of tiny wax pillars which are less than 100 microns apart. Water, which has a high surface tension, cannot penetrate through the tiny pillars and into the leaf. This creates a hydrophobic effect, forcing moisture and condensation to bead up and roll off the leaf. As the water beads roll off, they pick up dirt particles, keeping the lotus leaves clean and dry—this is referred to as the lotus effect.

For the last two decades, the building materials industry has looked to uncover innovation for building performance improvements and creating sustainable solutions which mimic biological processes.

Construction stakeholders such as architects, designers, specifiers, and building owners, can all learn from nature to improve the durability of products. One of these advancements includes products which mimic the microstructural properties of the lotus leaf to a create super-hydrophobic lotus effect. This use of hydrophobic technology increases the lifespan and performance of the exterior finish or coating of the building.

Performance in design

Designing a new building or recoating or recladding an existing facility comes with expectations to deliver a long-lasting structure and comfort for occupants. There are five factors which impact the performance of a building and the exterior coating:

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  Mechanical action, such as abrasions, hail, swelling, and building movement. For example, people come and go through the front doors and may congregate out front, resting against the side of the building. Ladders leaning against the outside of the building or extreme weather such as hail can also damage the structure or cause abrasions which compromise any coating applied to the exterior cladding.

• Air pollution, including organics such as nitrogen oxides (NO) and mineral materials such as dust. In California, forest fires blow smoke and soot across the environment. In rural areas, fertilizers used on farms release nitrates into the air. In cities, hydrocarbon soot from diesel exhaust and jet exhaust leaves behind a sticky black residue. These pollutants can deteriorate the coatings and appearance of the facade.
• Biological organisms, such as mildew or fungal growth. In coastal regions, algae is common on the exteriors of a building, creating an unappealing green appearance and decreasing the effectiveness of the coating. In damp, humid climates, fungal growth can propagate and bond to coatings, making it difficult to remove and leaving a deposit on the surface of the coating.
• Bulk water includes rain, dew, snow, humidity, and other moisture and water vapor. The coating is the first face to the elements and requires effective, reliable water resistance. However, a traditional water-based coating can soften when exposed to bulk water. The softer coatings become tacky and attract dirt which does not wash away easily.
• Temperature and light effects due to climate and ultraviolet (UV) rays. Similar to a person’s skin burning in the hot sun, temperature and light can also degrade coatings on the exterior of buildings, making them fade after years of exposure. Moving North to South, the amount of UV exposure increases significantly.

Architects, designers, and specifiers can select from a wide variety of coatings to help protect a building’s exterior wall.

Acrylic coatings offer a variety of protective characteristics including durability, fade resistance, and resistance to cracking, peeling, and chipping while bridging hairline cracks. They extend the lifetime of a structure’s appearance and protect it from the elements. Applicable in new construction or a recoating situation, such coatings provide a variety of aesthetic options and preserve the value of buildings by serving as a breathable, durable, attractive layer of protection.

Hydrophobic coatings are acrylic coatings which repel water. This enables faster drying of the surface, reducing the opportunity for mold, mildew, dirt, and other pollutants to grow or stick to the surface. They may be used for new construction or recoating existing buildings, and help the building maintain its aesthetic appeal and perform better against the elements, while lowering maintenance costs and frequency of recoating.

Though hydrophobic coatings offer several performance benefits, to mimic the self-cleaning capabilities of the lotus leaf, coatings must be 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 the 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 aesthetics. Hydrophobic coating offers additional armor and long-term value. With these applications in mind, super-hydrophobic coatings 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 coating 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 colors (e.g. lightness values greater than 55) traditional architectural coatings start to experience noticeable dirt pick and fungal and 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 technology, which provides longer durability than traditional acrylic coatings.

Safety and appearance retention

Hydrophobic coatings better resist mold, 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 percent in the total cost of ownership over a standard coating product.

Lower maintenance cost (elimination of yearly pressure washing) and longer intervals between recoating (result of improved durability) provide long term savings over traditional architectural coatings. Reference back to traditional coatings under durability, the same properties contribute to extending a building lifecycle.

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Boosting cleanliness

Using hydrophobic and super-hydrophobic technologies to create low surface energy and nonpolar structures, hydrophobic coatings repel water and resist dirt pick up.

As material prices continue to rise, building owners and contractors are looking for ways to improve building performance and extend appearance retention. While regular building coatings are formulated to be highly stable and resistant, research on innovative developments has driven finishes and coatings which offer smarter solutions.

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Reclad delivers super-hydrophobic armor to Edgewater Condominiums

Along the Atlantic Ocean in North Myrtle Beach, the Edgewater Condominiums needed an upgrade to the 10-year-old stucco facade. The decision was made to remove the cladding and reclad it with a new one. The board of directors worked with the project team for the 10-story condo building to specify 23,225.76 m² (250,000 sf) of continuous insulation (ci) wall system with a super-hydrophobic finish with self-cleaning properties.

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“The hydrophobic finish does a remarkable job at keeping the building looking clean and new,” says Chris Rush, president of the Edgewater Condominium Associations (COA) board of directors. “The buildings completed over a year ago look just as good as the building that was just completed.”

The system featured a continuous, air and water-resistive barrier (WRB) which helps the building prevent moisture intrusion. As added protection, the lack of fasteners in the adhesively applied continuous wall system further minimizes potential moisture and air intrusion into the substrate.

Specifying a ci wall system helped to lower the utility bill by 20 percent and reduced upkeep to maintain a cleaner, newer-looking building. The water- and weather-resistant properties of the hydrophobic finish provided additional protection against damage and water intrusion during three hurricanes throughout construction—Florence, Michael, and Dorian—which brought 120 km/h (75 mph) winds.

Makeover to defend Steamboat Grand Resort

The Steamboat Grand Resort in the popular ski area of Steamboat Springs, Colorado, sits at an altitude of 2103 m (6900 ft). The area is exposed to more than 300 days of sunshine per year and some of the highest snowfall totals in the state, wreaking havoc on traditional facades and water-based coatings. After 12 years, the exterior facade was worn by time and the weather, and was in need of a facelift to match the beautiful interior.

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The 328-room resort hotel was the ideal location for a super-hydrophobic coating with self-cleaning properties. The project team could also apply the new coating without disturbing guests and visitors, an added benefit to the hotel’s operations.

“The resort business is so conscious of curb appeal and, when you drive up to the property, the product almost sells itself,” says Jim Diner, vice-president
of ProCoat Systems, the applicator of the coating on The Steamboat Grand Resort. “The flat exterior wall coating imparts super-hydrophobic properties and has excellent weather and ultraviolet (UV) resistance. It was the best long-term, cost-effect solution out there.”

Conclusion

A building’s coating is its first line of defense, the initial layer of protection from the elements and human impact. Building owners, developers, and contractors can change the paradigm when it comes to long-term building performance and aesthetic appearance by specifying more durable coating solutions such as hydrophobic coatings.

Advancements in material science mean longer, more reliable resistance to the forces of nature, and nature has provided inspiration.

Author

James Howell is a product manager for Sto Corp. and is focused on facade claddings. He has a degree in business management and has more than 20 years of experience working with exterior insulation and finish system (EIFS), stucco, air, and moisture barriers in research and development, and marketing departments.

Source URL: https://www.constructionspecifier.com/hydrophobic-coatings-unlock-protection-against-water-intrusion/

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