What is Rising Damp?
Rising damp occurs when moisture from the ground is "sucked" into porous building materials from which walls are constructed. It does this through a process called "Capillarity".
What are the symptoms of Rising Dampness?
Rising Dampness can cause:
Does the plasterwork on the wall affected need to be removed?
When rising damp occurs in a wall it can carry salts into the wall fabric/plasterwork as the moisture evaporates at the wall surface. Two salts which are common with rising damp are chlorides and nitrates (Hygroscopic Salts). These salts are capable of attracting and absorbing moisture from the atmosphere when the relative humidity is high. This means that even if a damp-proof course is successfully installed the plaster may remain damp.
It is for this reason that wall plaster affected by rising damp should normally renewed in conjunction with the installation of a new damp proof course. Re-plastering should always be carried out to a minimum height of 1 metre.
Removal of Contaminated Plaster and Damp Proof Course Injection
Rising damp treatments may require the removal of salt contaminated plaster to the affected areas in accordance with British Standard 6576:2005.
A new damp proof course can be injected using Dryzone or Dyrods.
Once a damp proof course has been inserted, the moisture in the wall from the previous rising damp will start to dry out. As a general guide, the drying rate is given as 1 month for every 25mm of wall thickness (BRE Digest 163). This means a 230mm wall will take approximately 9 months to dry.
It is important therefore that the walls are allowed to "breathe" and wallpaper or other barriers to evaporation are not applied until the walls are dry.
Floor/wall junctions (solid concrete floors) may need to be sealed with Drybase liquid applied damp proof membrane.
A number of methods are available for re-plastering following the insertion of a damp proof course. A survey of your property will help decide which method is most suitable.
A few examples are:
Please note the above is a guide only and does not apply to every job undertaken.
Salt contamination is not only caused by Rising dampness.
Other sources of salt contamination of masonry and plaster are:
As these salts are often hygroscopic (Moisture Attracting), patches of dampness may appear and disappear depending on the weather. This can sometimes be confused with a leak occuring. This is why it is important to have a qualified surveyor investigate.
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