Rising damp can be defined as the upwards flow of moisture through a permeable wall structure. Almost all building materials are, to a certain extent, permeable and moisture is drawn from groundwater and transported via tiny pores â€“ termed â€˜capillariesâ€™.
A number of factors will influence this, changing the severity of the effect. These include
- pore structure of the masonry
- level of the groundwater
- rate of evaporation from the surface (influenced by ambient temperature and ventilation)
In modern homes, a damp-proof course is inserted around 150mm above ground level to physically stop the passage of moisture, but many older homes have no such luxury. Some have more primitive versions, like a layer of slate built into the wall, but most exist without additional protection.
The results can be:
- damaging erosion of the wall surface by salts carried in the groundwater
- compromised thermal qualities of the wall, resulting in greater heat loss due to the conductivity properties of water
- decorative damage, including blistering paintwork, peeling wallpaper and flaking plaster
- a stuffy, moist internal environment which is unpleasant to live or work in and can cause health issues
In particular, certain building materials (which happen to be prevalent in older structures) are more absorbent. Lime mortar, which is often recommended by building professionals for solid wall structures to allow a level of breathability, is particularly absorbent. Compounding this, the level of evaporation from a large, solid walled structure is significantly less than a thinner wall â€“ as the surface area to volume ratio is lower.
Old buildings are comfortably the most susceptible to this phenomenon, therefore, and any readers with a property built pre-1950 should be extra vigilant.
Solutions to rising damp can take a number of forms, some focused on addressing the underlying issues â€“ some focused on simply barring the moistureâ€™s progress.
Ventilation and heating
Background heating to increase the ambient temperature of the structure, combined with increased ventilation, will promote greater levels of evaporation. Even when more drastic solutions like those discussed below are taken, this step is important to allow the wall to dry out.
Introducing a damp-proof course (DPC)
A number of proprietary systems exist to do this, though it is beyond the scope of this article to recommend one. Suffice to say, DPCs can be injected, introduced with a damp-proofing â€˜creamâ€™ or installed utilising damp-proofing rods. Systems of electrolysis have also historically been utilised, though the true effectiveness of this is under debate.
Be sure to choose a reputable firm, should you wish to explore this option. Poorly installed solutions could leave gaps that would only exacerbate and localise the problem.
Re-plastering with a damp resistant system
Once a solution has been applied, contaminated plaster can be removed and replaced with a water resistant variant. Whilst this may hold off future problems for a period, it should also be noted that solid walls need to be able to â€˜breatheâ€™ to allow internal moisture to escape. Water-proof plaster products may not be permeable in this way and advice from a surveyor is recommended to ensure you donâ€™t compromise the wallâ€™s future condition.
As with the insulation industry, DPC installers suffer from a poor image driven by the actions of a minority. Nevertheless, anyone considering such an installation should be very careful in their selection and should seek the advice of an independent professional before committing. That professional â€“ ideally a chartered surveyor â€“ can also monitor the installation as it takes place, ensuring the highest quality of work possible.
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