David Clifton, technical manager of Munters, says there is more to the property damage restoration process than hot air.

For the property restoration team the first task is always to find out what type of water has caused the damage. Clean water would usually come from a burst water pipe or leaking water tank. Grey water would come from overflowing drains or a leaking washing machine and black water would normally be the result of flooding from an external source and, or sewerage contamination. The most important question to be asked if the water is in any way contaminated is, how much have the building, its contents and the occupants been affected?

How much the water penetrates is not only a result of how long it has had to settle. Penetration is also a sign of whether the damage is horizontal or vertical, that is running down or through the building.

The most crucial aspect of the drying process is to ensure all saturated materials that have altered in size and shape and have no further value are removed from the property – for example loft insulation material. A sample is however, retained for inspection by the loss adjuster or insurance company representative.

The main objective in the drying process is to lower the vapour pressure or absolute humidity to a point which allows maximum evaporation to take place. It is as much as three hundred times faster to dry free water using any type of dehumidifier than with a wet vacuum. One of the first tasks is to remove all wall coverings, particularly heavy vinyls, as they represent a vapour barrier which slows the drying process down to a point where no evaporation can take place.

Any wood that hasn't been damaged beyond repair must be dried in the correct way. As wood suffers dimensional changes very quickly extreme care must be taken. The most common way of controlling the rate of drying so that it is wood friendly is with a Humidistat connected to the dehumidifiers. This way the humidity can be lowered slowly so as to limit further damage.

Moisture contained within wood adjusts to its surrounding environment and when this changes quickly, as in the case of water damage, then wood will soak up free water. The wood will also suffer if the humidity remains high for any length of time, though small variances have very little effect.

The permeability of the subject material is important when looking at the drying programme and the time it will take. The denser the material the longer it will take. The amount and size of the pores in any material also affects the drying time. Engineering bricks are very dense with very small pores, as are some types of concrete. Plaster is also a very dense material. It has a moisture content of approximately 1 to 1.5%mc in a dry condition and 3% when saturated. So it might be necessary to remove the plaster in order to let the more porous bricks dry.

Rates of moisture penetration into the material can be very slow. Average rates are approximately 12 to 15mm per 24 hours, which of course vary. As soon as the technician knows the depth, penetration and approximate density, which is calculated with calibrated instruments, a judgement can be made on the correct method of drying and how long it will take.

Scientific studies show that there are three main stages to drying. Firstly, the drying rate remains fairly constant. Here the danger is that the untrained person will believe that the surface appearance means the property is in fact dry, when all that has happened is the surface moisture has evaporated. The second stage focuses on the excess water that has filled the material's pores. As the pores become drier, liquid flow stops and diffusion commences, slowing down the whole process. The next step is to allow the excess moisture on the pore walls to diffuse through the material to the lower vapour pressure.

Because of all these factors and the variety of materials used in building it is difficult to quote an exact drying time. However, we are in the process of developing a system where given all the data on materials, densities, thickness and so on, we can arrive at an accurate drying time scale. This will be of obvious benefit to all parties, especially the insured.

We are also working on the further development of a remote monitoring system. The difference with our system is that we can control the level of drying by switching the equipment on and off, and by adjusting the Humidistat. This system would primarily be used for drying out water damage in remote locations.