Rising damp is caused by ground water moving up through a wall. Most walls are designed to allow some water in, however a protective physical horizontal barrier is usually installed at the base of walls as a damp-proof course to prevent water from rising further – averting damp as a result. Walls that do not have this damp-proof course may find that they will be susceptible to rising damp. This particular type of damp is found along the lower sections of walls, spoiling decoration and possibly leaving a characteristic tide mark effect on the surface, although it can also damage low level timbers too, such as floor joists, skirting boards, etc.
This is what everyone thinks of when they say they have a damp house. As the title says it the moisture from the ground rising in porous wall construction by means of capillary action, in the same way water would rise up causing a sponge in the sink. The way we know it is rising damp is the height is normally no more than 1.3 meters from the highest ground point, also there is normally a tide mark around this point. However, ground salts may go as high as 1.5 meters and can be seen as white staining on the walls.
The cure can be as simply as putting a chemical Damp Proof Course in place, but if the plaster has been compromised this will need to come off and be re instated using antisulphate products. This is in the form of a plastering system, which will hold back the salts. This is finished to a smooth finish ready to be re decorated thus allowing the wall to dry out at a rate of about 75mm a month in normal condition. Also, bridging of the Damp Proof Course can be a problem and this would need to be looked at to make sure this does not happen. Bridging can be the plaster is below the DPC to a new flower bed being installed against the outside wall .
Caused by water leaking through the walls, penetrating damp is usually caused by external defects in a building such as roof problems, faulty guttering, poor seals around frames and defective masonry walls or rendering/dashing for example. Homes with cavity walls are less likely to have penetrating damp issues, as the cavity provides ventilation and protection. However older buildings that have solid walls may find an increased risk of rainwater penetrating the building and leading to dampness. This type of damp can be identified through damp patches on internal surfaces such as floors, walls or ceilings. These patches can be seen to get worse when it rains, and can be normally found in the vicinity of an exterior defect(s).
Penetrating damp consists of moisture – usually rain, broken gutters occasionally floods penetrating the interior of the property from outside under wind or gravity. There are many things to think about with this ie roofs, walls, windows, doors, chimneys and so on each of which have their own problem areas Also, has the property had cavity wall insulation put in? This too can be a factor of penetrating damp.
We can tackle this problem from 2 ways. Firstly, the outside can in some situations be dealt with. As long as the outside has not been painted or rendered. This can be the easier of the options, and the cheapest however it will need to have a maintenance plan put in place for every 8/10 years. Secondly, we deal with this problem from the inside of the property, this is the long term solution to the problem, but can cause short term disruption to the home owners. This would involve the taking of of the plaster floor to ceiling, then using antisulphate to stop the salts then applying a tanking system re plastering using a antisulphate ready render. This will allow the walls to dry out at about 75mm a mouth in normal conditions.
We offer up to a 30 year guarantee for this type of works .
Ground Water and Hygroscopic Salts
Ground water contains soluble salts, the most significant of which are chlorides, nitrates and sulphates. When rising damp occurs, these pass with the water up the wall and are left behind when the water evaporates. Over many years of active rising dampness large quantities of these salts accumulate within the masonry and decorative surface, most becoming concentrated in a general ‘salt band’ towards the maximum height of rise as illustrated in the diagram on the left. Both chlorides and nitrates are usually hygroscopic, (i.e.they can absorb moisture from the surrounding environment) and, in general, the greater the amount of salts the greater the absorption of moisture – especially under humid conditions. Thus, even though rising dampness may have been controlled by the insertion of a remedial damp-proof course these salts alone can cause the wall and any contaminated decorations to remain damp. It is for this reason that specialist replastering is such an important aspect of rising damp treatment.
Further information on replastering as part of a rising damp treatment strategy can be found on our replastering as part of a rising damp treatment page. D&S Remedials offer a free no obligation estimate to cure your rising damp problems.
We offer up to a 30 year guarantee for this type of work.