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Dampness in buildings can arise from a number of different sources and it is therefore essential that in order to control dampness we need to understand how the building has been constructed, this is particularly important when dealing with older houses or buildings of historic interest, although it should be noted that dampness be it rising damp or penetrating damp does not just affect older properties.

Rising Damp or Penetrating Damp?

Damp is of great concern to many property owners and features heavily in many building surveys, but it is often misunderstood resulting in inappropriate and ineffective damp proofing repair measures and treatments, particularly in older houses, which in some cases only deal with the symptoms of the dampness and not the true causes of the damp. However the problems of rising damp or penetrating damp should not be underestimated.

Moisture in any building can result in decorative spoiling, plaster staining, mould growth and unhealthy and uncomfortable living conditions for its occupants. Excess moisture can also lead to render and plaster damage, salt contamination, erosion of brick and stone work and more importantly is likely to lead to the development of wood rotting fungal decay ‘wet and dry rot’.

Rising Damp

Rising Damp is caused by moisture rising up through porous masonry from the ground and is usually found in older buildings constructed without a damp proof course or where an existing damp proof course has failed or has been bridged.

Moisture rising up through masonry (whether brick or stone) carries with it soluble ground salts, including nitrates and chlorides, which can be deposited within the masonry as damp evaporates. 

Long term rising damp can result in a concentration of salts left at the maximum height of dampness and the height to which rising damp will rise would be governed by several factors, including the walls material, thickness, pore diameter and structure, the supply of water, the presence of impervious rendering /plaster and the rate of moisture evaporation.

The effects of long term rising damp can take the form of low level decorative spoiling and staining of paintwork and wall papers (which can resulting a distinctive tide mark on a wall) plaster damage and salt contamination as well as the decay of timber skirting boards, joinery and structural floor timbers. Severe dampness may also result in plaster damage and contamination (by hygroscopic salts; chlorides and nitrates) and therefore re-plastering of the walls can sometimes be required to provide a ‘non-spoiling’ decorative finish.

Rising damp is the result of capillary moisture and will therefore never take the form of ‘free surface moisture’ or ‘water droplets’ on a wall.

Penetrating Damp

Penetrating Damp can normally be broken down into two categories these being; lateral penetrating dampness (below ground) and vertical penetrating dampness, caused by general building defects above ground.

Lateral penetrating dampness normally occurs on external walls where the external ground levels are at a higher level than the internal floors and as a consequence dampness within the soil bearing against these walls penetrates the walls fabric. A typical example of lateral dampness is in a basement where external walls are built against the external (subterranean) ground.

Other typical causes of lateral dampness can be due to raised gardens and soil levels, flower beds, abutting garden walls, paths and pavements. Methods of controlling penetrating dampness below ground would depend mainly on the proposed use and the level of dryness required.

Vertical penetrating dampness is caused by building defects and poor building maintenance. Roof defects, leaking, blocked guttering and down pipes, will contribute to the most common causes of dampness and are proven to be responsible for a high percentage of dry rot attacks caused in buildings.

Cracked rendering, defective pointing, external coatings and blocked cavities, along with inadequate window and door sealants are also responsible for moisture ingress and along with internal plumbing defects and poor external drainage.

By far the most common cause of vertical penetrating dampness is defective rain water goods, guttering can be overgrown and blocked, damaged or simply past its sell by date.

I you suspect you have a damp problem….damp wall, damp floor or damp ceiling, be it rising damp or penetrating damp your first point of call would be to organise a damp proofing survey to correctly establish the cause of dampness.  

Once this has been established suitable damp proofing treatments can then be recommended to eradicate your damp problems for good.