Space technology for old buildings

There are one and a half million old buildings in Switzerland. We have to live with these buildings – indeed we want to live with them. Yet at the same time the country's energy consumption is increasing. According to the Federal Office of Energy, 4.5 million tonnes of light fuel oil and 3 million cubic metres of natural gas are imported every year, 43 percent of which goes up the chimney for heating. Anyone who wishes to cut down on fossil fuels must therefore insulate their home. But how do I insulate my historical building? Heritage protection would be none too pleased if the historical façade was covered with modern insulating panels.

Aerogel render is sprayed on with a professional rendering machine and then smoothed out. In the next step the soft render will have to be protected with a tough surface layer.

Stahl and his colleague Severin Hartmeier from Fixit’s central laboratory made it their task to take the insulating properties of render to a new level, and to develop a render that provides as much insulation as a polystyrene board. Years of research have now finally paid off: The product has come through laboratory testing, and initial trials on buildings started in July 2012. If the new insulating render holds up to its promise, the material could come onto the market in the course of next year.

Aerogel is already being used in the building industry, as cavity-injected wall insulation or in the form of insulating boards made from fibrous fabrics. So where is the problem? Why hasn't anybody already mixed aerogel with render? Thomas Stahl doesn't waste his breath on a lengthy explanation. He takes a transparent plastic box off the shelf and opens the lid: "Put your hand in and rub it a little". The aerogel globules really are extremely light, almost weightless, and can be held between thumb and forefinger. But as soon as you rub your fingers, it crumbles. After two or three rubs, a fine powder is all that remains of the wonder material. "And that was precisely our problem", says Stahl, "if we mix the powder with water and apply the render by hand, the results are good. But imagine if the render was pumped through the hose of a professional rendering machine at a pressure of 7 to 8 bar. There wouldn't be much left of our aerogel."

In order to make the render "machine-compatible", a tremendous amount of knowledge about the contents of dry render mixtures and their interactions with aerogel was required. And a series of tests – from palm-sized laboratory samples to weathering tests lasting for months. Eventually the researchers at Empa and Fixit found a solution, which they now want to have patented.

The samples of the aerogel render exhibited a heat conductivity of less than 30 mW/(mK) – twice as much insulation as the insulating render that is currently commercially available (see bar diagram on left). If the innovation asserts itself on the market, Swiss house owners will soon see a considerable reduction in fuel consumption.