Wall humidity – Part 1/2

Umidità - VimarkOne of the most degrading diseases plaguing housing is definitely damp in walls.

A problem that many buildings have especially old buildings. Moisture inside the walls over time causes a progressive deterioration of the materials, stains and mould on the walls, which have an adverse effect on the environmental microclimatic conditions and on health.

The strong presence of moisture in walls decreases significantly the degree of isolation of the wall/home to the point that, according to studies, environmental heat dispersion may increase up to 65%, causing discomfort and increasing heating costs.

The preliminary diagnostic phase is important and essential in order to proceed correctly with the wall restoration using the most suitable technique.
Humidity in masonry can manifest itself in many ways, due mostly to the different causes.

Structural water, humidity balance, construction humidity, accidental humidity, meteoric humidity, condensation humidity, rising damp or capillary action.

Umidità - VimarkL’acqua di strutturaStructural water, also called hydration water or crystallization and is made up of the percentage of water that is chemically bound with the building materials. The structural water is therefore closely related to the material and has no relevance to the degradation.

The humidity balance is the content of moisture in materials in thermodynamic equilibrium with the environment. The surface of materials absorb moisture in the form of water vapour directly from the environment in which they find themselves exposed and depending on the porosity of the materials. The greater the percentage of small pores, the greater the hygroscopicity of the material will be. Obviously within an environment where the relative humidity is high, the greater the equilibrium moisture content of the material will be. In addition, the environmental temperatures and the presence of hygroscopic salts will affect the parameters, which can affect the behaviour of the material considerably increasing the humidity.

Construction humidity is caused by the water used during mortar, plaster and concrete preparation. The excess water tends to evaporate during the hardening phase, bringing the structures moisture to physiological values. This type of moisture only occurs during the construction phase of building or at the end of renovation and restoration, disappearing gradually over time.
Accidental moisture normally originates from the breakage or malfunction of plumbing and heating systems, structural roofing, external doors or rainwater. This humidity is normally easily identifiable, it appears in the areas of the building placed in direct contact with the leak, and is generally easy and fast to fix.

Atmospheric humidity is a direct effect linked to atmospheric precipitation. It is more common on the external surfaces of buildings and can also appear on limited portions such as on ledges or windowsills. It mostly depends on wind direction and the porosity of the building’s materials. The facade plaster plays a primary role as its main function is to limit the infiltration of rainwater that finds a way to the internal surface exclusively via crack penetration passing through the walls. Atmospheric humidity is a therefore superficial and decreases within hours after the precipitation as a result of evaporation.

Condensation humidity is due to the increase in surface and interstitial density in the masonry caused by the passage of vapour present within an environment from a gaseous state to a liquid state. The condensation appears in the form of small water drops on waterproof coatings and in the form of dark spots on porous materials, especially in places with strong vapour production. This phenomenon occurs on cold surfaces, to be more precise, where surface temperatures are lower than dew point, referring of course to the type of environment in which it appears. For example, the problem is often evident in correspondence with poor thermal insulation due to the presence of structural thermal bridges such as corners, columns, beams, slabs, etc.

Interstitial condensation instead is related to the diffusion of water vapour penetrating the walls that divide environment temperatures and differnt humidity and occurs in the inner layers of the wall when they are not made correctly. Condensation humidity is therefore linked to the amount of water vapour present in the environment, to a poor thermal insulation, to weather conditions at the time, insufficient permeability to water vapour and technical errors in the succession of the wall layers. Being so directly tied to thermal and hygrometric dynamicsm of the environment, those both external and internal, it must last for long periods before causing a significant increase in moisture in the masonry enough to enhance the evidence and the extent of damp area.

Rising damp or capillary action occurs when water from the ground rises up through the bricks and mortar of a building by capillary action. The phenomenon has more or less evident factors depending on multiple factors such as the amount of water present in the ground, the size of the capillaries of the wall materials, the presence of waterproofing in the masonry and the evaporation capacity of the external and internal surfaces of the masonry.

Water-soluble salts are generally associated with rising damp, as well as sulfates, nitrates and chlorides, which, upon reaching the surface, crystallize due to the water evaporation. Capillary rising damp is easily diagnosed by observing the presence of obvious water stains (tide-marks) on the walls from the floor upwards, often accompanied by the presence of whitish efflorescence due to surface deposit of water soluble salts.
Wall humidity is therefore the main cause of degradation with a consequent reduction in living comfort.
These conditions of degradation can be:
chemical: hydrolysis, chemical attack from pollutants;
physical: chalking, peeling and blistering of the coating, plaster and finishing, crystallization of salts with the formation of saline efflorescence;
hygienic and sanitary: hygrothermal variation of the environment resulting in a decrease of the insulating capacity of the wall;
Biodeterioration: formation of mould, fungus and other organisms.