Rising Damp and Penetrating Damp
This Page is Currently Under Construction
Rising Damp and Condensation
At Miller Preservation Limited our experianced staff will identify your damp issuses within a property whither they be as the result of condensation, rising damp, penetrating or laterally penetrating damp as well as other potential issuses such a salt contamination of plaster.
Rising Damp
True Rising Damp is ground water rising through a building material due to the porous nature of the material and the physical property of water surface tension; i.e. capillary flow or the meniscus effect. It is important to distinguish the difference between rising damp and other forms of damp readings which can affect buildings such as:
- rain water penetrating through the structure
- faulty rain water goods (gutters, down pipes)
- contamination of hygroscopic salts
- surface condensation of atmospheric moisture
- interstitial condensation
There are also a number of perquisites for rising damp to occur:
- a water supply or damp soil at the base of a wall
- a porous or capillary rich building material used in the construction of the wall
- the absence of a damp proof course in the construction of the wall
It should also be highlighted that rising damp can also be a seasonal effected potentially only directly affecting a property during certain periods of the year, though the likely salt contamination would remain.
A simple experiment that a client could carry out to illustrate rising damp would be in place a common house brick into a basin or dish with a modest amount of water in it, say no higher than around 6mm or quarter of an inch (if you prefer). Leave the brick for several hours or even overnight and when it is inspected you will clearly see the physical attributes that allow rising damp occur.
To explain capillary flow and the meniscus effect consider the following example. Fill a normal drinking glass with water. Now look at the edges of the glass where the water meets the sides, you should be able to see a slight upwards curl in the water. This is the surface tension of the water or the meniscus trying to creep up the side of the glass, it is the same force that makes a water droplet form on a flat surface. If you where to place a very very narrow tube into the water so that the two "slight upward curves" overlapped the creep force strength would be sufficient to allow the water to rise up within the tube until the force of gravity on the weight of the water and the force of the "creep" equalise. It should be highlighted that as building materials do not tend to contain perfectly straight capillaries which are open only at the top and bottom rather they tend to run in numerous directions and are open in a great many points which means that evaporation will also factor in limiting the height attained.
Penetrating Damp & Laterally Penetrating Damp
Penetrating damp can in broad terms be though of damp within a property which is not caused by either rising damp or condensation of atmospheric moisture. Buildings in the UK carry a principle requirement that the building design should shed rain. It should therefore a rare occurrence for a new property to be affected by penetrating damp. A older property can with the passage of time and wear and tear from the weather, develop defects which can allow penetrating damp to manifest. :
- wind (disrupting roof coverings, etc)
- frost (damage to masonry)
- heat (solar gain can crack masonry)
- poor building practice (e.g., poorly constructed or detailed extensions, garages, conservatories)
- poor maintenance (leaking gutters, defective roof coverings)
- even just general ignorance of construction (e.g. inappropriately raised flower beds, paths)
can all contribute to penetrating damp problems with a property.
A specific type of penetrating damp requires mentioned. That type is lateral penetrating damp or damp which occurs below the effective ground level or damp proof level of a property. This will typically affect basements, garden flats or similar areas.
Below ground water is subject to pressure created by the weight of the ground water itself. Every 300mm of depth increases that pressure by around 30 grams per square centimetre which would give a pressure of 3 metric tonnes by the depth of 3 metres. This effect is the result of what is technically hydrostatic pressure. Given this situation special measures must be taken. As a general point the installation of a chemical damp proof course would in itself be of little practical use, further more specialist works will be necessary.