Read our blog post by our CSRT Surveyor - Dampness in Buildings - The Common Causes
Rising damp is a prevalent issue in older buildings, arising from the upward movement of moisture through their walls due to inadequate damp-proofing measures. This phenomenon can lead to various detrimental effects, impacting the building's structural integrity and aesthetics.
Symptoms of rising dampness include visible signs such as peeling wallpaper, blistering paint, and deteriorated plasterwork, which are indicative of decorative spoiling. Additionally, hygroscopic salts, notably chlorides and nitrates, may be carried into the wall fabric and plasterwork, resulting in salt patches and persistent dampness even after installing a new damp-proof course. The continuous exposure to moisture can cause erosion of the building fabric, leading to spalling brickwork, and damaging mortar, brick, and stonework. Furthermore, rising dampness diminishes the insulation properties of porous building materials, contributing to increased heat loss and a higher likelihood of condensation settling on the surfaces.
Timber elements in close contact with damp areas are also at risk of fungal decay and woodboring insect attacks, further compounding the overall structural issues.
To address rising damp, it is essential to undertake comprehensive remediation measures. Installing a new damp-proof course is a key step in preventing moisture from rising through the walls. However, due to the potential presence of hygroscopic salts in the affected plasterwork, it is recommended to remove and renew the plaster to a minimum height of 1 meter. This approach ensures the elimination of contaminated plaster and helps maintain the integrity of the newly applied plaster, thereby mitigating the risks of ongoing moisture-related problems and salt damage.
In summary, rising damp demands thorough attention and professional treatment to safeguard the building's longevity, structural soundness, and aesthetic appeal.
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:
Render Systems -Most companies use sand and cement render but we only use Dryzone Damp Resistant Plaster due to its excellent breathability properties. Dryzone Damp Resistant Plaster is applied as the base coat to the wall.
This is a breathable plaster (More breathable than lime plaster) but will not allow the passage of salts through to the surface. It has excellent thermal qualities. A finish coat of Thistle Multi Finish plaster is then applied to a smooth finish.
Older and traditional constructed buildings may require Lime re-plastering to meet conservation/listing requirements.
Plastic Polypropylene Membranes (Plaster Membranes AKA Cavity Drainage Membranes) or Drybase Flex Membrane are a useful way of isolating plasterboards and renders from salt contaminated surfaces. A plaster skim finish is usually applied on top of the plasterboard or render.
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.