The Problem 

Rising damp can be described as dampness resulting from water in the ground rising up through masonry by capillary flow. In order for this to happen there must be either no damp course or a failed damp course in place. Once in the wall, the moisture then evaporates out internally due to heating etc. It is at this stage that the evaporating moisture can cause the plaster to 'blow' and damage internal wall coverings such as paint and wallpaper. A further problem is caused by the damp containing soluble salts, as detailed below.


Hygroscopic salt migration

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. 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 re-plastering is such an important aspect of rising damp treatment.


The solution

In areas where rising damp is diagnosed all 'infected' plaster should be hacked off taking the walls back to the original brickwork (this is usually only up to about one metre high due to evaporation and atmospheric pressure). A chemical damp course will then be injected, forming a waterproof barrier and thus preventing any further moisture rising up the wall. The chemical used by Three counties damp is called Dryzone and is one of the market leaders in rising damp control. For more information visit www.dryzone.eu

Walls should then be treated with an anti-sulphate solution in order to neutralize any salts contained in masonry, and coated with an SBR slurry to form a barrier and give improved adhesion for the plaster. All re-plastering works carried out following the installation of a new damp course are done using Tarmac Limelite renovating plaster. This has numerous benefits over normal plaster such as inhibiting mould growth, providing a salt barrier and allowing the brick wall to dry naturally.

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