Read our blog post by our CSRT Surveyor - Dampness in Buildings - The Common Causes
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:
Solving damp issues can also involve undertaking external works to a building.
There are numerous external defects which can result in dampness affecting the structure of a building. It is very important that when diagnosing a dampness issue internally that an external inspection of the property take place. This quite simple procedure if often missed by most damp proofing companies and this can result in dampness issue persisting after remedial works have been undertaken internally.
Below are examples of typical problems which we encounter that cause dampness issues to buildings.
Typical external works include:
Lowering Ground Levels
High external ground levels built up against a wall can result in the damp proof course being bridged. This means that moisture from the ground can bypass the damp proof course and rise up the wall. High ground levels can also allow rainwater to splash over the damp proof course and penetrate the wall.
The ideal solution is to lower the external ground levels so that they are below the internal floor level and to also ensure that the damp proof course is always a minimum of 150mm above the external ground level. By simply undertaking the above, the evaporation from the base of the wall will vastly be improved and this should reduce dampness. In most cases only a small amount of ground needs to be removed from the base of the walls.
Removing External Render
Blown, cracked and damaged render will often need to be removed or repaired if it is allowing moisture to penetrate the fabric of the building. On older buildings it is particulary important that lime is used for any repairs/renewal.
Re-Pointing of Walls
Poor pointing will allow moisture to penetrate the fabric of a wall. It is therefore important that this is kept in good condition. When it is in poor condition then re-pointing should take place. On older buildings it is particulary important that lime is used in the re-pointing mix. If the walls are particulary prone to rain penetration then consideration may also need to be given to the use of an external breathable water repellent.
Sub Floor Ventilation Improvement
Poor sub floor ventilation or a complete lack of it can result in dampness ocuring under an internal suspended timber floor. This can then result in large amounts of moisture accumulating on the base of the walls. There is also a risk of fungal decay and attack by wood boring insects.
Ventilation should be improved by increasing the amount of vents or replacing/cleaning out existing vents.
Rainwater Goods & Drains
Defective rainwater goods and drains are also other possible sources of dampness externally. These should be kept clean and any repairs/renewals undertaken when required. This is not a service that our company offers.