Rising damp in building may be defined as the vertical flow of water up through a permeable wall structure, the water being derived from ground water. The water rises through the pores (capillaries) in the masonry by a process loosely termed ‘capillarity’. In other words, the masonry acts like a wick. Warmwall offer a range of specialist rising damp treatment solutions to prevent this problem.
The height to which the water will rise depends on several factors including pore structure and rate of evaporation. Masonry containing a high proportion of fine pores will allow the water to rise higher than a coarse pored material; basically the water is carried up the wall in the finer pores and not those of large diameter. The average size of pores in masonry gives a theoretical rise of around 1.5 meters but where evaporation is severely retarded, for example by the use of impervious membranes, moisture can sometimes rise in excess of 2 meters.
The major paths through which the water rises are the mortar beds. For water to rise through the bricks then it must cross a mortar bed. In effect the mortar beds form the only continuous pathways for water rising through the wall. If a house is built from impervious bricks then water can still rise through the mortar bed but if an impervious mortar is used then no water will rise even if the bricks are very porous. The mortar beds will form an important part in the chemical treatment for rising dampness.
Ground water contains small amounts of soluble salts, the most significant of which are chlorides, nitrates and sulphates. 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 bond’ towards the maximum height of rise. Frequently, the concentrations of these salts are very low towards the base of the wall.
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. Warmwall offers a two step process of rising damp treatment:
To provide a ‘dry’ wall and a suitable surface to take new decoration, the Warmwall Damp Master System involves two fundamental processes:
- The insertion of the chemical damp-proof course.
- Removal of old contaminated plaster-work and decorations, and replacing with specialist replastering to prevent the passage of any residual moisture and contaminant salts from pass to the new surfaces from the underlying masonry.