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Rising Dampness and its Control 

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Rising Dampness

 


Moisture rises as a result of capillary action where moisture from the ground can rise up within the walls and mortar beds up to approximately one metre above ground level, and the symptoms of which can be a problem in both dry and wet conditions which is the condition known as 'Rising Damp'.  One or more of several symptoms which identifies rising damp are stained decoration, lifting wallpaper, softening plaster, mould or fungi in timber and wall surfaces. Concrete floors can also suffer from rising damp.

All modern buildings are now constructed with a damp-proof course (DPC) installed. A DPC is a layer of waterproof material or membrane that is introduced during construction which forms a barrier between the rising moisture. The DPC for brickwork consist of a reinforced indestructible plastic the width of the brick or block which is rolled out onto the new brickwork 150 mm above the outside ground level before the remainder of the wall is built onto it, which effectively creates a continues horizontal moisture barrier at this level throughout the building. Though a DPC can exist in older properties from the 1900, the materials used was not very durable and over time would eventually break down due to being brittle, or becoming so. In older properties a DPC may not exist at all.

Different types of Dampness

Rising damp can be treated in a number of ways, but before selecting and commencing a cure an inspection should be made as dampness may occur internally as a result of other faults, and may not be what is classed as rising damp at all. These other causes could be due to condensation or defects in the vertical DPC at window and doorframe opening or adjoining walls. Another less obvious cause is where the DPC has been bridged within the cavity of the wall by the buid-up of falling debris. This problem can also exist externally, where soil or debris is piled up against an exterior wall, or even as a result of concrete, flags or other finishing materials being laid higher than the DPC onto the external wall. In which case, removing the material to 150mm below the DPC will cure the problem. If the bridging is within the cavity, the bricks would need to be removed, usually from the external leaf of the wall, and the cavity cleared to a few inches below the DPC.

 


Treatments


Rising damp can be prevented by one of several methods. These involve inserting a new DPC membrane of a physical nature, or by using electro-osmotic or chemical systems.

Physical Damp-proof Courses

Faulty or non-existent DPC were at one time replaced by removing a 1m run of brickwork, into which the plastic DPC was rolled out. This section of the brickwork course was then replaced, except for the space where the roll was positioned. A further section of brickwork was then removed, allowing the roll to be further rolled out, with the brickwork replaced behind. More recently, developments have been made in cutting equipment, which allows the cutting of a narrow slit using a tungsten tipped chain saw or grinding disc along a mortar joint, into which the plastic DPC is inserted. Due to the weight and loading of the wall, it is only possible to work small section at one time, usually about 1m runs; and the cut is finally packed and held with slate and grouted with mortar before moving on.

Electro-Osmotic Process


This system involves the introduction of a very small and perfectly safe electric current into the wall just above ground level through a series of copper anodes inserted into the brickwork. The charge repels the rising moisture molecules and forces them down the walls and back into the ground. As long as this tiny positive charge is maintained, the protected walls remain dry and totally free of damp. 

Chemical Injection Method


This method is installed by a contractor, or could be successfully attempted by a reasonably competent property owner, but it should be pointed out that contractors are approved to do this type of work, and only they can provide a guarantee for the installation, which will probably be required by the bank or building society.
Basically, a silicone water-repellent is injected under pressure or by gravity, into a series of holes drilled into the wall at specified intervals. The solution spreads outwards left and right from each injection, which creates a horizontal damp proof course at the base of the wall. The chemical injection of walls should be carried out on both sides of the wall, unless there is a specific reason why this cannot not be done internally.

Refinishing Walls and Woodwork

Internally, rising dampness causes damage to the plasterwork and skirting boards, which should be removed and renewed. In the case of the injection system, the walls should be rendered with a sand and cement mix, up to a height of 1m, and the mix should contain a waterproofing additive. Skirting boards should also be renewed, and treated with wood preservative on the back.

 

 


 

 

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