Exterior architectural coatings

Interview with alexa tan


Alexa Tan works for Evonik Coating Additives in the Smart Surface Solutions (S3) competence center, based in Singapore. She has worked in the coatings industry for 19 years, mainly in marine, industrial, and architectural coatings. She is now involved in product development projects and is currently working on a project to improve dirt pick-up resistance. 


Exterior architectural coatings face a variety of natural and man-made elements that have an impact on their appearance. 

The main challenges I often hear in architectural exterior coatings are dirt pick-up resistance and stain resistance. Exterior architectural coatings are subjected to harsh environmental conditions such as rain, snow, extreme temperatures, humidity, and UV rays. These elements degrade the polymer in the coating causing erosion and chalking.

These coatings are also subjected to mildew growth and dirt pick-up, which negatively impact their appearance. In urban areas, the increase in number of motor vehicles has caused air pollution which accelerates dirt pick-up. Both professional and DIY painters are looking for ways to be cost-efficient. If they can develop a coating that is easy to clean, shows less dirt pick-up, and is stain resistant, this will reduce labor and maintenance costs.  

the right coating can help to improve dirt pick-up resistance in several ways.

There are many ways to improve dirt pick-up resistance. This can be achieved by influencing the surface porosity, the surface energy, and hardness. Striking a balance is very important here, as the downside results in compromising on elongation properties. It may also make the surface more porous, resulting in increased dirt pick-up.

Hydrophobic coating technology is one of the most promising approaches to dirt pick-up resistance. In hydrophobic coatings, water beads more readily and it maintains a high surface energy, preventing the water from plasticizing the film.

At Evonik Coating Additives, our TEGO® Phobe hydrophobing agents can be used in paints as impregnating agents and primers. These additives offer optimal production and enables systems such as silicone paints and exterior silicate paints, which can both breathe and are water repellant. In the coatings industry, a substrate is considered hydrophobic and water repellant if it cannot be wetted easily by drops of water.  

tackling the challenge of dirt pick-up requires standardized, realistic testing methods. 

A feasible and rational artificial accelerated lab test method is needed to simulate actual dirt pick-up conditions. The composition and the proportion of the solution sources, the application modes, and the cleaning cycles are key factors in determining the test method. There is a working standard for ASTM, inviting experts and professionals to share their views and experience. In other regions, the most widely used method is GB/T 9780.

At Evonik, we wanted to reflect the actual climate, so we expose our panels to UV rays before we subject them to be sprayed by dirt from our DPU machine. This is followed by washing cycles. Our team in research and applied technology is constantly working with Smart Surface Solutions group to refine and standardize our test methods. In addition, we are working on the next-generation DPUR products through my current project.