Summer Condensation is a rare phenomenon whereby whole floors appear to sweat during the summer.
This typically affects stone, wood, concrete and vinyl floors in homes, schools and sports halls etc. It can be very worrying and it is difficult to understand why a floor has become wet and slippery. It is in fact due to a thin layer of condensation forming and, quite remarkably, this happens during the summer months! Fortunately it is extremely rare as it only occurs once or twice every ten to twenty years, possibly slightly more often in South, South-West and Western coastal areas of the UK. During the summer we sometimes get a few cooler days in succession and where these are immediately followed by a mass of warm humid air rolling across an area of the country, then these are the exact conditions necessary for Summer Condensation to occur. The floors have cooled to below the dew point of incoming warm air so they gather condensation as it arrives. Moisture can appear on walls too, but is almost never noticed. Windows, often only north facing ones, gather condensation to both the inside and the outside panes at the same time however this is generally fairly short lived and not a problem.
The main points to note:-
Summer Condensation occurs when warm moist air moves slowly across an area of the country immediately after a few successive cool days which have caused the floors to have cooled sufficiently so that the are below the dew point of the incoming warm air, it is then that we may see Summer Condensation. If it is windy the air generally mixes so much with less humid surrounding air that its humidity decreases and nothing happens.
Many people, including surveyors, never see this problem and information about it is so scarce that when it does occur it is difficult to diagnose without a thorough knowledge of the underlying science and a Sherlock Holmes like ability to solve problems.
On the few occasions that I have been called in to assist, I was able to reassure concerned home owners that it was nothing to worry about and they took up my advice to take no action and later thanked me. I also managed to avert a private school from spending tens of thousands of pounds repairing a supposedly failed damp proof course in their main hall floor. However I am aware of several other cases where whole floors have been unnecessarily replaced and wild goose chases embarked upon at extremely high cost looking for subterranean sources of the moisture that simply did not exist.
This information should help home owners, surveyors, building facilities managers, sports centre managers, caretakers and cleaners as long as they can locate it.
What can be done to prevent the problem?
Absolutely nothing can be done to prevent it happening as it is an atmospheric/weather phenomenon that we have to live with. Some may suggest that it will become more common but it is just part and parcel of the random nature of our wonderful British weather. Well, maybe if you knew it was coming, you could close all your windows and switch on the heating!
What should you do if it does occur?
The best advice is to wait for it to go away. You may wish to collect the water by “squeegeeing” the floor and collecting the water. This works better rather than trying to mop it up. For wooden floors this process is strongly recommended, and using a wet and dry vacuum cleaner can help prevent a major disaster where the moisture can cause the wood to expand and the floor to spring up in places due to the wood swelling. As it is happening it is best to keep windows and doors closed though this will not prevent it happening. Once it has happened it is advisable to open windows and doors and use fans if available. Turning the heating on will help even though this is counter intuitive, and may seem unnecessary in summer. If air handling is available this should be run on maximum using the dehumidify mode. An industrial dehumidifier will collect condensation but will be slow to dry the floor.
The types of floor that are most likely to be affected: All cold floors including stone, tiled, wood, vinyl, concrete, metal, especially those on any form of concrete will be prone to being affected.
Dr Tony Cowling 2018