The pathologies found on the facade they can affect the entire surface or just some parts.
The first distinction, depending on theextension And:
- punctual pathology, if referred only to particular or small superficial extensions;
- zonal pathology, if it repeats itself several times on the facade or on the same floor;
- diffuse pathology, if it completely affects one façade or a large area
of the same.
Facade pathologies: the position
When the part of the facade affected by the pathology is identified, it is important to document its position in reference to the height or floor, in order to be able to verify, over time, whether the restoration treatment performed has completely eliminated the pathology or whether it recurs.
Furthermore, if the pathology recurs, to understand the causes, it will be possible to perform periodic monitoring on that same surface.
Facade pathologies may involve:
- only the external surface of the plaster (e.g. paint),
- also affect the substrate (e.g. plaster),
- involve the entire support (e.g. the thickness of the wall).
Current technology provides diagnostic tools that allow us to observe what happens both outside and inside the walls. The investigation techniques can be non-destructive, semi-destructive or destructive towards the wall system under examination.
Facade pathologies: the investigations
They are investigations:
- non-destructive those applied to structures or surfaces that do not require demolition, do not alter the appearance or material of the masonry itself;
- destructive those that require the use of large samples, destroying or modifying the masonry system in a mostly irreversible way;
- semi-destructive those that do not cause destruction or irreversible changes, but are limited to using samples from small holes or very small samples.
Facade pathologies: when they can manifest themselves
There are pathologies that they are born already at the time of constructionusually due to design errors, called physiological errors. For example, an undersized load-bearing wall will be subject to subsidence and cracking, which will also affect the external surfaces.
Even the construction of an extension of the building with a new volume, carried out without particular precautions such as adequate wall fixing or, alternatively, the execution of a structural joint, without considering that it is much more important to respect the natural structural and expansion movements of the two different bodies, will lead to inevitable very evident cracks.
Most pathologies, however, manifest themselves during the life of the building; pathologies usually arise due to:
- natural aging of the building,
- lack of maintenance,
- incorrect maintenance and/or restoration,
- natural traumatic events (earthquakes, floods, fires, volcanic eruptions, etc.).
In the first two cases It should be noted that most of the damage is caused by water, or by elements contained and transported by the water itself: rainwater, water with an acid pH, water from condensation, water from splashes caused by road traffic, water that bounces off the cornices, nebulising and corroding, water in the form of frost, water from capillary rise, water in the form of aerosols and even salt mist, water from percolation of damaged sheet metal work, water as an activator of disintegrating chemical reactions, etc.
Together with water we frequently find the saltssolubilized and conveyed by the same, which cause chemical destruction through molecular transformations and physical destruction given by the enormous growth in volume when the salt passes from the ionic phase of the solute to the macroscopic crystalline phase.
Pathologies in historical facades
We list, in summary, the pathologies that occur most frequently in historic facades.
Some are macroscopicvery widespread and well known. Others are less obvious and more subtle, more difficult to recognize. Often they are present simultaneously in an integrated and combined way. We list them briefly:
- rising damp;
- water seepage from the roof, from overhangs such as balconies, from sheet metal works;
- problems due to concentrations of salts carried by water;
- attacks by plant organisms (molds, lichens, grass, bushes);
- degradation of lime plasters and calcareous stone elements, due to chemical aggressions such as acid rain or smog (the alkaline calcium carbonate transforms into gypsum, i.e. calcium sulphate, which is acidic);
- degradation of plaster due to physical erosion by the wind;
- cracks and crazing of various nature and size;
- washing away of colored finishes;
- incorrect and inappropriate use of materials or maintenance and restoration techniques (cement, paints and synthetic film-forming and non-breathable coatings, incorrect consolidations, etc.).
