The coating on Pilkington K Glass™ is very hard and is difficult to scratch. Unfortunately, it is slightly rough (although not in a visible sense), so it may collect marks and dirt in a way which is difficult to clean off. It is inadvisable to use it as single glazing for this reason with the Pilkington K Glass™ coating to the exterior*.
If Pilkington K Glass™ is used in single glazing with the coating facing the room, it may also promote the formation of condensation. This is because the coating acts as a barrier to heat, keeping the glass colder than ordinary single glazing. Because the surface is colder, condensation will form more readily and in larger quantities than on ordinary single glazing.
The only circumstances where Pilkington K Glass™ would not generally promote condensation on the room surface is when the external temperature is always higher then the room temperature. This can occur if the room is a cold store, or if the building is in the tropics.
*Note. Some manufacturers of proprietary systems are using Pilkington K Glass™ in situations where the coating is on the external surface, apparently without significant problems of dirt and marks over several years of use. However, NSG Group do not and will not take any responsibility for the durability and performance of Pilkington K Glass™ when used in this manner.
Pilkington K Glass™ can be used in secondary glazing, with the Pilkington K Glass™ as the inner pane with the coating facing the air gap between the two panes. Although the coated surface will have to be cleaned occasionally, it is generally protected by being in the cavity and washing with clean soapy water or a clear window cleaning solution should maintain it in good condition.
There is a risk of the coating being marked by the sliding sashes when used in secondary sliding glazing systems.
As with any secondary glazing, there is a risk of condensation on the inner surface of the outer pane, unless the air gap has some ventilation to the outside, possibly just through gaps in the existing window.