Creation of the chemical barrier
The realization of a chemical barrier involves the creation of blind holes (pre-drilled holes) with diameters of 14-16mm using an electro-pneumatic roto-percussion drill. The injection is carried out using equipment consisting of a pumping unit, equipped with pressure gauges to keep the pressure constant, which varies from 0.5 to 0.8 atmospheres, according to the porosity of the masonry and other parameters, after which it is passed to the use of non-toxic and ecological formulations (siloxane resins) aqueous solution.
The preparation operations of the facing and the holes, together with the injection modalities, will have to be carefully planned and only after having carried out a preliminary inspection on the global situation and case by itself, since too many parameters influence the type of technological approach.
The resins, used to prevent the capillary rise of water, are non-toxic and totally safe both for the operators and for the inhabitants of the building. The substances used are organic derivatives of silicon, such as silanes and siloxanes. The two formulations that Dar.De.Ca. privileges in dehumidification works, they consist of a liquid silicizing concentrate that acts in depth, on a water basis and injected with a low pressure pump; the other product is a special silane / siloxane-based cream in an emulsion form that acts more slowly and from the surface, injected with a hand pump.
To complete the construction of the chemical barrier carried out, at least four finishing stages are required, necessarily carried out in this order:
closure of the holes used for the injection of the formulation;
flaking of dilapidated plaster;
cleaning and desalination of wall parameters;
restoration of plasters and paints.
The water-repellent action of the barrier chemical compounds starts already after a few hours, but in some cases it takes longer, due to the completion of all the chemical reactions essential for the complete cross-linking of the formulation. After this time, the injection holes can be closed with an anti-shrinkage mortar or resin (i.e. with low elastic modulus), compatible with the type of masonry and with the formulation used.
The complete dehumidification of the structure, above the chemical barrier, takes place in very long times: as an order of magnitude we can consider and estimate one centimeter of thickness per month. Even with good ventilation, almost continuous insolation and not very thick, the time required to dispose of the residual humidity can be several months, and during this period it is desirable (for a good result of the intervention) that on the vestments saline efflorescences appear (called “bleeding”).