Everything you needed to know about self-cleaning glass

Phil Brown, European regulatory marketing manager at Pilkington UK, discusses the facts behind self-cleaning glass.

It was 16 years ago that Pilkington Activ became the first commercially available self-cleaning glass. Since then, we’ve sold more than 10 million square metres of it, which is enough to cover the football pitch at Wembley 1,380 times.

The advanced glass is popular for everything from conservatory roofs to commercial facades. But, considering the long history of float glass, self-cleaning glass is still a relatively new product that some in the industry still have misconceptions about.

The first thing to note is that not all self-cleaning glass is the same. Pilkington Activ, for example, is dual action, which means it works in two stages.

Stage one uses a ‘dirt eating’ photocatalytic reaction to break down organic deposits such as mud, while stage two is based on the ‘water loving’ hydrophilic coating, which spreads water evenly over the surface of glass to form a thin film instead of forming into droplets. This helps to wash dirt away, preventing the formation of drying spots and streaks.

It’s important to install self-cleaning glass that has been tested to the necessary standards. A new European Standard, EN 1096-5, has been introduced that evaluates the self-cleaning performance of coated glass. This standard allows specifiers to differentiate between glass with a classified self-cleaning performance and without.

The way self-cleaning glass is installed can have a big impact on its performance. The minimum recommended angle for a roof containing self-cleaning glass is 10º from horizontal. Any less and the rainwater may not run off and wash dirt away effectively.

Sealants and gaskets that are lubricated with silicone oils can’t be used with certain self-cleaning glass products, including Pilkington Activ, as they can mask the hydrophilic and photoactive actions of the coating – the technologies that make the glass self-cleaning. If silicone is used and left on the glass, silicone contamination causes water beads to appear on the surface when it is raining or wet.

A number of alternative sealants, gaskets and cleaning agents can be used that are compatible with self-cleaning glass.

There are a couple other factors to keep in mind in order to help homeowners and building managers to get the best results out of dual-action self-cleaning glass.

When self-cleaning glass has been stored in a warehouse for a long period prior to installation, it may take up to seven days to become fully activated. This is because the activation of the glass occurs via a chemical reaction between UV rays from natural daylight, oxygen and the coating. After then, it will continue to work as long as it’s exposed to daylight, even in dull winter weather.

The amount of cleaning the glass needs depends on how dirty it is and the amount of rain it is exposed to. During long, dry spells or if the windows are particularly dirty, some manual cleaning might be required, either by gentle hosing to replicate rainfall or by using a soft cloth and warm soapy water.

It’s rare that self-cleaning glass needs to be rinsed, but if the water used is very hard, then it should be softened with a domestic softener or by adding a couple of drops of detergent.

There are some cases where self-cleaning glass might not deliver the results expected of it. For example, wind-blown spray in coastal areas can cause salt crystals to adhere to the surface. As salt is an inorganic contaminant, it can’t be broken down by the photocatalytic action of Pilkington Activ. While this is worth considering, the technology will make the glass cleaner than ordinary glass after a light hosing or rainfall.

Lead carbonate can also leach from flashings in rainwater and be deposited as a white stain onto glass. This effect can occur on any glass, not just self-cleaning glass, but is one of the things it can’t remove by itself.

Inorganic contamination is not broken down by the self-cleaning coating and can be difficult to remove. It’s recommended that where lead is used, and there is a risk of rainwater run-off onto the glass, is treated with patination oil (or similar) to reduce the risk of leaching. Lead flashings should be treated on both sides, particularly if they lap directly onto the glass.

After self-cleaning glass has been installed in a building, care must be taken during any further construction work to avoid staining or damaging to the coating.

Rusty deposits, plaster products or adhesives can affect the coating. So, after building work is completed, the glass should be cleaned as soon as possible by rinsing with water to remove all traces of dust and abrasives that may have accumulated during construction.

Understanding the science behind self-cleaning glass, and how its best used and installed, will help to spur its uptake.