Information about mould and mould disease
For rising damp to affect property three basic conditions have to occur. There has to be a contact between the structure and the ground, the underlying ground has to contain enough moisture and the construction materials need to be porous enough to allow for water to flow.
The first two are fairly obvious and self explanatory but the third one warrants some explanation. The construction materials which are mostly known to suffer from rising damp are bricks, stone and to smaller extent concrete. Technically any material which has a porous structure such as timber, plaster, earth, clay, clay blocks and others may suffer from rising damp. On the other hand, non-porous materials such as high density bricks, steel, glass and some impervious stones (slate) are resistant to rising damp.
Rising damp typically reaches to about a height of 1 meter but some local condition may crate variations. In rising damp problems the water (moisture) rises through the wall or floor construction by means of capitally action. The water carries minerals and dissolves more from the construction material itself. The water evaporates from the surface leaving behind mineral deposit. The minerals accumulate and gradually block the pores in the materials forcing the water to travel a bit further up to achieve evaporation.
Rising damp affects properties when water prevention materials fail or are missing altogether. The most traditional materials to prevent rising damp in structures are damp proof courses or damp proof membranes. The combination of ageing, building movements or ground movements can cause damp proof course to crack allowing water to enter the structure.
Damp proof course can also fail due to careless construction and in particular when new extensions to building are added or thermal insulation is carried out. The most frequent causes are raised ground level, external rendering or internal plastering.
Another common problem are wall ties, which should have a central drip to stop water crossing the wall cavity.
Although not very frequent but nevertheless occurring failure is accumulation of construction debris at the bottom of the cavity wall. Mortar accumulated at the bottom of the wall cavity can bypass the installed damp proof course causing rising damp.
Traditional solution to rising damp problem would include installation of a new damp proof course of various type, which will however require stripping of the walls of plaster. Less demanding solution is the reduction of the problem rather the complete elimination. This could be achieved by construction of water drains around the property to lower the water table, clearing of the drains making sure they are not constantly soaked in water and to replace moisture and mineral loaded finishes with more moisture tolerant materials.
The most permanent solution is physical insertion of a new damp proffer course. Unfortunately it is a labour intensive and time consuming process which makes this permanents solution quite expensive. Damp proof course can be also reinstated by chemical injection of water resistant solutions (silicon or aluminium stearates) into the wall material or by installation of so called electrical damp proof course which involves positive electrical charges to counteract capillary action.
Damp proofing is often followed by “tanking” or treatment of wall surfaces with a layer of water impervious either bitumen or rubber based materials.