What Is Rising Damp?
Despite what many may think, rising damp is not the common form of dampness encountered within buildings, this is left to condensation. Many older buildings however are affected by rising damp to some degree.
Rising damp on buildings is commonly defined as the upward flow of moisture through a permeable wall structure. The moisture derived from ground water rises through the pores (capillaries) in the masonry by a process loosely referred to as capilarity, which in turn causes the masonry to act like wick.
Rising damp can vary in severity depending on a number factors, such as the level of groundwater, the pore structure of the masonry i.e. brick, stone mortar etc, together with the rate of evaporation away from the wall surface.
Rising damp can often require treatment due to the number of undesirable and unsightly consequential effects, such as;
- Decorative Spoiling Moisture and ground salts present due to rising damp can cause wallpaper to peel, plaster to deteriorate and paint to blister
- Erosion of Building Fabric Ground salts introduced into the wall as a result rising damp can attack and dissolve the binders in brick, stone and mortar, which in turn can cause them to lose their strength and structural integrity.
- Increased Heat Loss Dampness in porous building materials may cause a reduction of insulation properties as air in the pores is replaced by more conductive water. i.e. the thermal conductivity of a wet brick has been found to be twice that of a dry brick.
What Causes Rising Damp?
Rising damp commonly occurs when moisture from the ground is sucked into the porous building materials from which walls are constructed through a process known as capillarity.
The potential height, to which moisture can rise in a masonry wall, largely depends on the absorbency of the components from which the wall is constructed. The pore structure of certain types of materials such as lime mortars can result in a high degree of absorbency and therefore are likely to be more susceptible to rising damp.
The flow rate of water through the structure is largely dependent on the pore size, shape and connectivity. The pore size in brick/mortar can be as small as 0.001mm radius, which in turn provides us a theoretical height of rise of around 1.5m high. Therefore rising damp can be found to have risen well in excess of 1.0m, the height commonly claimed to be the maximum.
Rising damp is inextricably linked with other forms of dampness, such as hygroscopic damp.
Subsequently, due to rising damp hygroscopic (moisture attracting) salts, such as Chloride and Nitrate contaminate the plasterwork. Once present in the fabric of the building they can result in dampness by attracting and absorbing moisture from the atmosphere.
When hygroscopic damp affects a wall it becomes a cause of dampness in its own right and can continue to be a persistent problem even in the event that rising damp has been successfully rectified i.e. by installing a new chemical damp proof course (DPC). This is why it’s imperative to carry out specialist replastering as part of the treatment process.
What’s The Cure?
For successful treatment and eradication of rising damp you must first stop the source of dampness. This is commonly achieved by introducing a new chemical damp proof course into the base of the wall. Following the installation of the damp proof course, it will then be necessary to replace the existing damp affected plaster internally with a new specialist cement-based render which will be suitable for use in damp conditions and subsequently hold back any residual moisture and hygroscopic salts that remain present within the wall structure, and will also prevent slats from migrating through to the surface of the new plaster.
To successfully prevent the progress of rising damp through a wall structure, it is necessary to have a suitable and effective damp proof course. A damp proof course is a horizontal barrier located at the base of the wall which in turn prevents the upward flow of moisture. Many older buildings were constructed with a physical damp proof course; however the materials which were utilised in early 20th century, such a pitch and bitumen were very thin and overtime would become brittle and deteriorate which in turn would lead to ineffective barrier against rising damp.
Installing a new physical damp proof course into existing walls can be hazardous, expensive and not to mention impractical. Today the most practical and effective way to eliminate rising damp is to install a chemical damp proof course, commonly achieved by injecting thixotropic creams into the wall, which subsequently turns the existing mortar bed into a waterproof barrier.
The new chemical damp proof course should be installed no less than 150mm above external ground level in order alleviate the risk of splash back from the external surfaces which in turn could potentially lead to bridging of the damp proof course and subsequent low level penetrating damp.
When installing a new chemical damp proof course it is imperative that treatment is carried out in strict accordance with BS8215: 1991 Code of Practice for Design and Installation of Damp-Proof Courses in Masonry Construction.
Biocraft South West is an established damp proofing company, with extensive knowledge in the diagnosis and successful remedial measures proven to eliminate rising damp.
To arrange a survey of your property or for further information regarding remedial damp proofing, contact us today. We cover Andover, Bath, Bristol, Chippenham, Devizes, Marlborough, Oxford, Salisbury, Swindon, Trowbridge and Warminster.