Householders FAQs - Windows - Technical
1. Why have I got external condensation on my windows?
Under particular weather conditions, dew (or frost) forms on any unheated surface (the ground, roofs, walls, cars etc.) exposed to a clear night sky. In the past, this effect has not happened on the glass in heated buildings, since the heat that escapes through the glass warms the glass up slightly as it passes through. Even conventional double glazing allows sufficient heat to escape to prevent dew forming on the external face of the glass.
However, insulating units incorporating Pilkington K Glass™ are sufficiently resistant to the passage of heat (i.e. it has such good thermal insulation) that in certain positions and in some weather conditions, it is now possible for the dew to form also on the external face of the glass. This is one visible manifestation of having superior insulating glass. [An analogy can be made with frost on roofs - those with good loft insulation can remain frosted for a long time, while those without quickly defrost.]
In order for this to happen, the glass needs to be exposed to large areas of the night sky. Intervening trees, bushes or other buildings, which block off part of the sky, reduce the effect. Other 'microclimate' effects can also alleviate it. It is possible to get a situation where some windows have external condensation while others nearby do not.
This is a fundamental physical effect, installing another Low E double glazing unit or turning the unit around will not eliminate this phenomenon.
In countries, such as Sweden, where most glazing is at least as good as Pilkington K Glass™ units, external condensation is a well known and accepted fact of better comfort and thermal insulation.
2. Why have I got a haze/milky appearance on my windows?
Haze is an optical phenomenon which makes the glass look like it is covered in a very fine, uniform, layer of dust when viewed from an oblique angle or viewed under strong light incident on the glass at an oblique angle.
Pilkington K Glass™ can, under certain lighting conditions, display this phenomenon to a limited extent.
The reason for this is that the Pilkington K Glass™ coating is not as smooth as the glass surface. While this is not obvious to the eye when examining the glass, some people who regularly handle Pilkington K Glass™ can tell which side the coating is on by the feel of it.
The optical effect of the slightly rougher surface is to scatter a small proportion of the light incident on it (in exactly the same way as a thin layer of dust would, which is why it looks similar). With Pilkington K Glass™, the amount of scattered light is generally less than half of one percent of the light coming through the window, so under most viewing conditions it is not obvious. However, when incident sunlight is at an oblique angle and the view through the glass is of a shaded area, then the scattered light can become more visible, giving rise to the appearance of haze.
Most coated glasses are susceptible to the phenomenon of haze, to a greater or lesser extent. The amount of haze on Pilkington K Glass™ is limited as far as practicable, and is generally better controlled than on its direct competitors in the field of low emissivity coatings.
3. Why do my net curtains look grey/dirty?
The benefits of reduced condensation and high thermal insulation obtained from using Pilkington K Glass™ are due to the presence of a special transparent metallic type coating on one of the surfaces of the double glazing unit. This ultra-thin coating is transparent but has a very small effect on white light transmission.
Pilkington K Glass™ has high light transmission and often appears indistinguishable from clear float glass. For this reason it is recommended that the presence of the coating is confirmed by the use of a K Glass™ Detector after installation. However, the coating does have a pale straw coloured tint and when a light coloured object or material is viewed through the glazing, depending on local circumstances and conditions, occasionally a slight darkening effect may be seen.
This may make net curtains or Georgian Bars look grubby or discoloured in certain situations.
Unfortunately, there is no way of overcoming this characteristic, although it does confirm the presence of Pilkington K Glass™ in the windows.
4. My double glazing units have failed, who will repair them?
You need to refer in the first instance to your window supplier who will inspect the units and then take up the matter with the unit supplier if appropriate. This is not something that Pilkington is able to assist with directly since your contract is with you installer. If Pilkington units are installed and considered to be at fault your window installer will take up the matter with the supplying Pilkington company directly.
5. My window supplier says he has installed a Pilkington patterned glass but it doesn't look right, can you help?
You do need to take this up with your installer. In order to help please browse through our range of Pilkington Texture Glass and the Pilkington Oriel Collection patterns.
6. The labels that were on my windows have left marks can you advise on cleaning them off?
Cleaning of Glass
Glass should normally be cleaned with a clean cloth and a clear non-abrasive cleaner, such as clean soapy water or a proprietary window cleaner. For glass with a patterned, etched or sandblasted surface, a stiff bristle or nylon brush can be used to remove dirt from the recesses in the surface.
If the glass does not become clean using the above methods the the following can be tried.
Use a mild acid (e.g. vinegar) or a mild solvent (e.g. methylated spirit), taking care not to spill any of these on other surfaces or materials.
If neither treatment works then the glass will need to be abraded and re-polished. this is likely to be expensive and should be left to experts. The process may result in some optical distortion where the glass surface has been removed.
Special Notes on Cleaning
Organic solvent cleaners should be avoided on mirrors since they may attack the backing paint.
Leaded Glass should only be cleaned with a clear non-abrasive cleaner. The cleaner should be of a type that does not remove the patina (aged surface finish) of the lead.
Patterned glass, acid etched glass and sandblasted glass should only be cleaned with a clear non-abrasive cleaner. Any insoluble material in the cleaner may deposit in the recesses of the etching or sandblasting and may be very difficult to remove.