What types of Damp are there?
Updated: Jul 21, 2020
The most common kind of damp issue will often be put down to a leaking pipe or joint connector. Another common leak will be around a shower tray, bath or sink. Caught early enough, plaster, timber, plasterboard, etc will simply dry down and after a short drying time, you will be able to redecorate. Left undetected for some time, it could lead to more damaging and potentially costly, Dry Rot.
Then the next all too common complaint is Black Mould which is a consequence of surface condensation. Surface condensation is normally an issue that can be a problem for many properties during the winter months when we tend to close windows to keep the heat in and the cold out but subsequently shut out any fresh, less humid air which leads to a condensation event. Repeated as a daily occurrence, black mould will soon start to thrive.
After leaks and condensation we are then left with structural damp. This can take the form of:
Bridging Damp - commonly this will be raised external ground levels or debris in a cavity. When the mortar breaks down around the lower courses of brick, rainwater can 'bridge' across to the internal decorated side. This will generally show up as a damp patch or a low level tide line just above the skirting. If the plaster is sound all you would do is prevent or repair the cause of the bridge and the plaster will dry out. All you would have to do is redecorate. Other defects such as cavity insulation of failed wall ties can also create a bridge.
Penetrating Damp - rainwater penetration from faulty pointing or guttering defects. Flat roofs can also lead to penetrating damp but this is more commonly described as a roofing leak.
Rising Damp - Contentious one this one as some would say there is no such thing!
Lets address this point. To a degree, I would agree with this opinion. On the flip side, DPC's, damp proof courses were introduced by Victorian building engineers to combat a problem with poor sewers drainage around new build developments. The introduction of slate to prevent water from the ground creeping up the walls came about in the 1870's and was written into building regulations ever since then.
Brick, mortar, timber, concrete will all act like a sponge and accept water which just like a sponge does, will rise up through the pores of a sponge. Hence labelled as Rising damp.
The common failure of an inexperienced surveyor, damp proofer or builder would be to not understand the reason behind water from the ground rising up the walls. Quite often, a building that is over a hundred years old may not have a DPC or that it does and it is defective. There could be every chance the structure did not need a DPC or was not built with one but the materials used, such as lime, wattle and daub or cob, allowed the structure to become damp without major internal damp defect but dry down in the summer and so on. However, for someone suggesting the damp can be treated they may very well have applied an external render, or repointed lime mortar over the top with sand and cement or replastered walls internally with gypsum and taken it down to the floor. Quite often, it will be poorly thought through work that brings about damp issues to a property that for a very long time, had been absolutely fine!