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. Credit: Fixit AG |
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.
Rendering
is the most suitable way of maintaining the look of an old house.
Cutting insulating panels to size (and shape) is also a cumbersome
business when lining winding staircases, round arches and supporting
walls. “An inner lining of insulating render is considerably quicker to
apply”, says Empa building physicist Thomas Stahl. “The render also lies
directly on the brickwork and does not leave gaps where moisture could
condense.
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.
World record for insulators
But
what does this marvellous render from the Empa labs consist of? Stahl
and his colleagues decided on the best insulating material that can be
produced industrially: aerogel. The material, which is known as “frozen
smoke” because of its appearance, consists of around 5% silica—the rest
is air. Aerogel was used back in the 1960s for insulating space suits,
and has 15 entries in the Guinness Book of Records, including “best
insulator” and “lightest solid”.
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.
Source: EMPA
