Condensation Patterning on Glass

When condensation forms on a glass surface, the rate of formation and appearance of the condensation can vary across the surface if there are materials present on the glass surface. This variation may be random, but may also show up as distinctive patterns. The most common contamination is from finger marks, but any contamination that creates a water-repellent surface layer, such as grease, glazing compound, suction cups, protective pads, excessive cleaning creams etc., may produce these effects.

The surface contamination that causes these effects results from a very thin layer of material usually transparent, which in normal dry conditions may not be detectable when viewed normally the glass may appear to be scrupulously clean, but will show marks when condensation is present.

The surface marking can sometimes be removed by cleaning the glass with an ordinary window cleaner or degreasing agent. Some marking may however, prove more obstinate in nature. For example, deposits from glass carrying suckers or processing protections can form chemical links with the glass surface, making them very difficult to remove.

These variations in appearance under condensation conditions do not indicate any fault in the glass. The surface contamination has no effect on any mechanical or physical property of the glass, other that its appearance under these abnormal conditions.

It should be considered by anyone who has condensation patterning on the room surface of insulating glazing units, that the presence of condensation indicated that the conditions in the room may be detrimental to other items, they should consider how to improve ventilation to the room.

The appearance of glass should only be assessed under normal viewing conditions as specified by the Glass and Glazing Federation, viewing standard 4.10.