Now, glass paint to keep metal roofs cool on sunny days

Scientists have developed a new, environment-friendly and inexpensive paint out of glass that bounces sunlight off metal surfaces - keeping them cool and durable.
"Most paints you use on your car or house are based on polymers, which degrade in the ultraviolet light rays of the sun," said Jason J Benkoski at the Johns Hopkins University Applied Physics Lab.
"So over time you'll have chalking and yellowing. Polymers also tend to give off volatile organic compounds, which can harm the environment. That's why I wanted to move away from traditional polymer coatings to inorganic glass ones," Benkoski said.
Glass, which is made out of silica, would be an ideal coating. It's hard, durable and has the right optical properties. But it's very brittle.

To address that aspect in a new coating, Benkoski started with silica, one of the most abundant materials in the Earth's crust.
He modified one version of it, potassium silicate, that normally dissolves in water. His tweaks transformed the compound so that when it's sprayed onto a surface and dries, it becomes water resistant.

Unlike acrylic, polyurethane or epoxy paints, Benkoski's paint is almost completely inorganic, which should make it last far longer than its counterparts that contain organic compounds. His paint is also designed to expand and contract with metal surfaces to prevent cracking.
Mixing pigments with the silicate gives the coating an additional property: the ability to reflect all sunlight and passively radiate heat.

Since it does not absorb sunlight, any surface coated with the paint will remain at air temperature, or even slightly cooler. That's key to protecting structures from the sun.
"When you raise the temperature of any material, any device, it almost always by definition ages much more quickly than it normally would," Benkoski said.
"It's not uncommon for aluminum in direct sunlight to heat 70 degrees Fahrenheit (21 degrees Celsius) above ambient temperature. If you make a paint that can keep an outdoor surface close to air temperature, then you can slow down corrosion and other types of degradation," Benkoski said.

The paint Benkoski's lab is developing is intended for use on naval ships. But it has many other potential commercial applications.
"You might want to paint something like this on your roof to keep heat out and lower your air conditioning bill in the summer," he said.
It could even go on metal playground slides or bleachers. The paint would be affordable as the materials needed to make the coating are abundant and inexpensive.
Benkoski said he expects his lab will start field testing the material in about two years.