Rising damp is a type of moisture problem that occurs in buildings when groundwater is able to rise up through porous building materials like masonry or concrete. This happens when there is a lack of an effective damp proof course (DPC) or when the DPC is damaged or bridged by high ground levels.
When rising damp occurs, moisture from the ground is drawn up by capillary action and into the walls of the building. This can cause damage to the internal and external walls, including staining, peeling paint, plaster damage, and decay by wet and sometimes dry rot, to built-in floor timbers, not to mention mould, mildew growth and the health risks associated with damp conditions.
Photo Courtesy of Advanced Damp
How Common is It?
Rising damp is not very common in damp properties. According to some sources, it affects between 5% and 10% of damp properties, while others estimate it at less than 5%. Note that these percentages are based on the number of damp properties, not the total number of properties in the UK. There are many other possible causes of dampness in walls that are often mistaken for rising damp such as leaks, condensation, and penetrating dampness that can also cause similar symptoms and should be properly diagnosed to determine the appropriate course of action.
The Cure
There are several ways to prevent or treat rising damp, including installing a new damp proof course, applying waterproof coatings to walls, if the walls are below ground level, and it is important to address rising damp promptly to prevent further damage to the building.
The most effective cure for rising damp is to install a new damp proof course (DPC). A damp proof course is a layer of waterproof material that is inserted into the walls at a height of at least 150mm above ground level, which creates a barrier to prevent moisture from rising up through the walls.
There are several methods for installing a new damp proof course, including chemical injection, physical insertion, and electro-osmosis, which is now outdated. The best method will depend on the specific circumstances of the building, such as the type of construction, the severity of the rising damp, and the accessibility of the affected areas.
In addition to installing a new damp proof course, wall plaster will need to be replaced with a special renovating wall plaster.
It is important to note that rising damp should be properly diagnosed by a qualified professional, as misdiagnosis or incorrect treatment can lead to further damage to the building.
Courtesy of Safeguard
Previous Methods
Porcelain tubes
Porcelain tubes are a type of damp proofing method that involves drilling holes into the wall and inserting porous ceramic siphons that are supposed to absorb damp and evaporate it from each tube. The theory behind this method is that the fine pores of the ceramic clay would draw dampness out of brick and stone by capillary action, and the angle at which the tubes were installed into the wall would cause the moist air to flow away by gravity. However, this method has many drawbacks and is not widely used or recommended by experts. Some of the problems with porcelain tubes are:
Salt accumulation in tubes may increase moisture
Air-flow sometimes inadequate
Tubes commonly set in hard cement mortar
Unsightly appearance
Therefore, porcelain tubes are not a reliable or effective way of curing rising damp.
Electro-osmosis
Electro-osmosis is an important phenomenon in many applications, such as chemical separation techniques (notably capillary electrophoresis), microfluidics, nanofluidics, soil remediation, and some years ago, for damp proofing. In damp proofing, electro-osmosis can be used to create a water-repellent barrier in a wall by applying an electric potential across electrodes inserted into the wall. The electric field causes the water in the wall to move away from the cathode (negative electrode) and towards the anode (positive electrode), thus preventing rising damp. This method was used extensively back in the 1970's with varying success and has now been superseded by chemical injection.
Author: Tony Waring is a Chartered Building Engineer (C.Build E MCAB), an Associate of the Royal Institute of Chartered Surveyors (AssocRICS) and a member of the Faculty of Party Wall Surveyors (MFPWS). He has over 30 years of surveying experience and 20 years as an engineer.
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