Introduction

Damp walls are an inconvenience often found in buildings. A wall is "pathologically damp" when the water content that characterises it, expressed as a percentage, exceeds 3%. The situation becomes critical when there is a large quantity of water and the wall cannot dispose of it, in the presence of significant quantities of salts, during bad weather conditions.

The deriving effects are the degradation of the walls and the plaster, the loss of thermo-insulating capacity, detached wallpaper and paint, the rise of efflorescence, the appearance and growth of mould, algae, bacteria, etc, with series repercussions for the health of those living in the home.

The functioning principle of the macro-porous, dehumidifying plaster is found in the very high surface evaporation determined by its characteristic macro-porous structure. Traditional plaster withholds humidity and doesn't allow it to evaporate. This causes water and hygroscopic salts to dynamically accumulate in the wall and cause its degradation. On the contrary, the macro-porous structure of the dehumidifying plaster ensures its convenient hygrometric equilibrium.

In other words, the macro-porous and dehumidifying plaster absorbs water from the wall and encourages evaporation outwards. This characteristics, which is similar in equal measure to that of a sponge, is a fundamental element which should be taken into account, which could cause some problems if not considered.

Plaster Breathability

The processes mentioned introduce the concept of permeability to water vapour and its influence on phenomena governing hygrometric equilibrium in walls. The elements to consider are defined by the "coefficient of resistance to vapour passage (μ)”, a scientific measure of the capacity of a material to counter the crossing of water vapour (the lower the coefficient the greater breathability of the material, air is μ = 1). Here are a few examples of the breathability coefficients:

All the materials composing the SANATIGH dehumidifying cycle have a coefficient between 9 and 11, to ensure the parts composing the entire "plaster system" are consistent with one another and together can provide a very healthy living environment.

It is interesting to also note that in the presence of surfaces characterised by a normal evaporation level, the height of the rising damp is normally between 2 and 5 times the thickness of the wall, while in the presence of poorly breathable surfaces or with coatings preventing evaporation (plaster and paint with poor breathability), the height of the rising damp can reach and exceed levels between 10 and 12 times the thickness!!

Some useful tips

The macro-porosity and permeability of dehumidifying plaster is obviously also efficient against liquid elements in contact with them. In fact, the macro-porous plaster, if placed in direct contact with rainwater stagnation, for example near footpaths (especially if not sloped), quickly soaks up the water. Before applying the plaster, you must therefore check that the slopes of the footpaths enable a rapid outflow of rainwater. You are also advised to create the skirting (10-15 cm) of the outer facade with a different material, which is less absorbent and that acts as an isolating layer from the footpath surface.

The macro-porous plaster pushes the water in the wall outwards regardless of the coating completing the dehumidifying system. If the final layer (putty coat, paint, etc.) is not adequately breathable the effects can be disastrous (Figure 3). The putty coat, paint or finish of a dehumidifying, macro-porous system must have permeability characteristics to vapour consistent with those of the dehumidifying system. For example, on plaster such as SANATIGH, SANAWARME, CALEOSANA, the value m, of the finish, should not exceed 11.