Principles of drying

Drying is a process which involves evaporation of moisture from a surface into air which has a lower relative humidity than the material itself.

Building materials used in construction can be placed into one of two categories in terms of moisture absorption/retention; permeable and non-permeable. Permeable building materials, such as brick and plaster and, to a lesser extent, timber can absorb and retain large quantities of water. Conversely, they will dry out relatively quickly, aided by assisted drying techniques.

Non permeable materials used in flooring and paint coatings are generally resistant to moisture ingress. The down side to this characteristic is that they prevent moisture evaporation when water is introduced unexpectedly. A damp wall that has been painted with vinyl paint or a concrete floor overlaid with carpet tiles can take months, if not years to dry out naturally.

Unfortunately building construction is neither straightforward nor consistent. Invariably both material types are used in tandem which creates conflicting views of how best to approach the drying process. We often use the analogy of placing a wet sponge inside a sealed plastic bag. The likelihood of it drying out without natural air exposure is remote. For this reason, some form of assisted drying, as well as targeted stripping out of damaged or moisture inhibiting materials, is normally required to speed up the process.