Self-cleaning windows on trial

Glass manufacturer Pilkington has developed a self-cleaning glass that is undergoing trials in Ireland, Austria and North America.

The Activ material designed for external windows incorporates a dual acting coating using hydrophilic and photo catalytic properties to eliminate water, organic and inorganic deposits from the surface of the glass.

The protection is continuous and lasts the lifetime of the product, it is claimed. The glass eliminates the need for window cleaning - a major concern with skyscraper blocks - and is expected to be introduced to the building trade later this year.

The key element of Pilkington Activ self-cleaning glass is a microscopically thin, transparent coating of a specially developed compound. This patented coating is bonded permanently to the surface of the glass by a special manufacturing process.

The overall thickness of the coating, which has several distinct chemical layers, is around 50 mm. The surface coating has two important chemical properties which, when combined, make the glass self-cleaning. First it is hydrophilic.

It attracts water and causes it to "sheet" on the surface of the glass, preventing the formation of separate droplets and ensuring that loose particles of dust and dirt can be washed naturally from the surface during normal rainy weather.

Secondly, it is "photo catalytic" - ultra violet (UV) radiation, always abundant during daylight hours, causes it to react chemically with unwanted dirt and organic deposits, oxidising them and breaking their adherence to the surface of the surface.