Q. We have mould growing in the bathroom, in the corners of several rooms and on the side of the wardrobe. I read that a high humidity level caused this. Can a dehumidifier fix this and do I run it on full for 24 hours before letting the humidistat take over?
This is a typical question that I come across often.
First of all mould starts to grow at a relative humidity (RH) level of 68%. The recommended RH for a home is 50%-55% or even 45%-50% if it is freezing outside. You can easily see that if any mould grows that the air is too moist.
If the humidity levels are way too high you will end up with stained ceilings and walls, peeling paint and/or wallpaper and other damp related problems. I had these problems with a tenant recently. She told me that there was a stain on the roof so after checking that it wasn’t a leak I was sure it was the excess humidity in the apartment that was the cause. My solution was to expain that the apartment needs to be vented more often and I also bought the tenant a moisture absorber which worked a treat.
What I suggest is that you buy a low cost hygrometer which will give you a true reading of the RH levels in your home. If the RH reads more than 60% then a dehumidifier could definitely help in bringing the moisture levels down and getting rid of your mould problem. When using a hygrometer make sure to measure the RH in different rooms as each room, or part of the house, will probably have a different reading.
When you use a dehumidifier for the first time you should run it on a high setting in order to extract as much moisture in as short a time as possible. The length of time that you run the high setting depends on the RH percentage of your area plus other factors such as living activities which include how often people shower or cook etc. One home might find that running the high setting for 24 hours is sufficient, another home might need to run the high setting for a week or two.