Once the components of a plaster mortar, and any criticality attributable to them, in order to determine the predisposing and triggering causes the phenomena of “pathological” degradation, which can undermine its integrity and physiological decay, it is necessary, as a next step, to analyze the factors that compete for support.
Even before proceeding with the creation of the plaster, the surfaces on which it must be applied (walls or ceilings) must fulfill specific prerogatives which, if neglected already in the design phase, can contribute to thetriggering degradation dynamics.
A thorough analysis, therefore, cannot ignore from the following areas of investigation:
- hygrometric state and degradation of the support and plaster;
- resistance of the support and crack pattern to damage the plaster;
- irregularities, out of plumb and plaster thicknesses.
Hygrometric state of the support
In order to carry out the correct diagnosis of the phenomena of “pathological” degradation regarding plasters it is necessary, first of all, to define the interactions between water (as an element, in its various forms: liquid, steam, ice, capable of triggering, by its nature, the premature decay of the covering) and the building envelope (walls and floors).
Humidity and the effects of degradation on plaster
The plasters, already at the time of their application (on walls or floors), are subjected to a incessant work by external forces (think, for example, of the force of gravity, meteoric events, movements of the support, etc.) which, over time, cause its decay.
The layer of petrified mortarapplied on the wall or on a floor, can be assimilated to a polyphase system (solid, gaseous (pores), and liquid (any water present in the pores)), characterized by a high bond strength, provided by the binder (lime, cement , etc.), whose thermodynamic equilibrium aims to reduce the total energy, bringing the mortar back to its primordial state (insubstantial sand) through irreversible dynamics of “intergranular disaggregation”.
When water comes into contact with building materials, it predominantly triggers i alteration phenomena (which often act synergistically: contributory causes), understood as the cause of the thermodynamic process which leads to an increase in entropy of the system due to the increase in the “degree of disorder” between and of the phases constituting the plaster matrix.
Water, and any substances conveyed by it (soluble salts, gaseous substances, particulates), is capable of triggering, as a chemical agent, the dynamics of transport, storage and contact between these substances and construction materials.
The actions of degradation, attributable to water, are essentially of “chemical” type And “physicomechanical”.
The effects of degradationon plasters, attributable to water, can be classified as:
- effect on resistance (reduction of cohesion and adhesion characteristics);
- hygrothermal effect (modification of thermal and hygrometric performance);
- hygienic effect (proliferation of spores and molds as well as pathogens in humid environments);
- aesthetic effect (crack patterns, stains, crusts, patinas, efflorescence, disintegration).
