Self Cleaning Windows? Just too Good to be True!

What is self cleaning glass?

Self cleaning glass is glass which has been thinly coated with titanium dioxide, an inorganic pigment that is used in a variety of products including sunscreen (reflects UV rays), toothpaste and as a whitener in white paint.

To put it simply, self cleaning glass uses a dual-action process in which organic dirt is broken down by daylight and is then washed away by rain, thus making it easier to keep clean.

More about how it works

Self cleaning glass works by two processes:

1. Photo-catalysis - the action of sunlight onto the surface of the glass eats away dirt. It does this by absorbing the UV component of sunlight which then breaks down any organic material on the surface of the glass.
   
2. Hydrophilicity - instead of forming droplets that run down the window in rivulets leaving streaks, the rainwater spreads out as a continuous sheet washing the glass clean..

Does it always work ?

Jeff Howell, exploring the pros and cons of self cleaning glass in The Telegraph (June 27th 2005) concluded that self cleaning glass is “self-cleaning as long as it doesn't get dirty”.

He contends that reality is often somewhat different to theory. Whilst self cleaning glass surely performed well in laboratory tests the same conditions seldom apply in real life. How often do upstairs windows, sheltered by lintels, arches and eaves get really soaked by rain? If rain is lashing against one side of the house, the other will surely remain relatively dry and therefore unwashed.

Jeff interviewed one manufacturer of self cleaning glass who admitted that their product is only "self-cleaning" as long as it is regularly hosed down with water, and even then it works best when the water flows slowly down an incline - such as on a conservatory roof - rather than straight down, as on normal vertical windows.

So.... no easy answer to your window cleaning problems I’m afraid! Best stick with the professionals....