“Drinking walls” could be mould-busters in super-airtight homes

Researchers in Germany say they have found a way to make walls harmlessly absorb moisture to combat the risk of mould in airtight homes.

Porous glass flakes added to plaster allow the walls to "drink" when household activities produce steam, then release the moisture gradually so that acceptable levels are maintained.

The manufactured porous glass works as a humidity-control agent because its pore size, volume and particle form can be exactly controlled, unlike naturally occurring additives, say scientists at the Fraunhofer Institute for Silicate Research ISC in Würzburg.

Air-tightness is the holy grail for energy efficient home design but, when activities like showering or boiling big pots of pasta send up clouds of steam, energy savings go out the window when people throw it open to get rid of the unwanted moisture.

In collaboration with Bayreuth University and the company Keimfarben GmbH, Fraunhofer scientist Ferdinand Somorowksy and his team are developing supplements for paint and plaster that "drink".

They selected manufactured porous glass flakes for the additive because pore size, volume and particle form can be controlled – an advantage the naturally occurring alternatives don’t offer.

It will take another two years before the moisture regulating plaster reaches the market.–

They tested Vycor glass, adjusting the process parameters to modify the pores. The glass particles can be manufactured cheaply in fibre or flake form while other materials with absorption properties, such as zeolite or ceramic, can’t be. Filler material can be produced with a pore size ranging from between just a few nanometers to several micrometers. 

"A minimal change in pore size adapts the material for different temperatures and various applications, such as living areas, rooms with consistently higher humidity or basement rooms," Somorowsky said.

In tests, researchers demonstrated that the glass-flake and plaster mixture absorbed considerably more moisture than other materials, and then released it slowly after the steam-producing activity stopped.

As humidity increased, the mass of the glass-flake infused plaster increased more and consequently absorbed more water compared to the reference materials. 

"In a room with a volume of 30 cubic meters, the walls and ceiling offer approximately 40 square meters of surface area that could be used for a moisture regulating plaster," Somorowsky said.

"In order to reduce the humidity from 72% to 47%, some 180 ml of water needs to be absorbed.

And our glass flake plaster can actually adsorb more than a half litre of water." 

Mold spore inhibitive substances can be added to the plaster as well.

Now the project partners are examining how the mixture works under additional paint layers and wallpaper. They estimate that it will take another two years before the moisture regulating plaster reaches the market.