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Weathering and air pollution compromise the preservation of historic buildings made of stone. The concept of the consolidation of materials is introduced to overcome this problem, or at least to reduce its severity. The consolidation consists of introducing a chemical substance into damaged stone for restoring its original mechanical properties, or into undamaged stone for preserving it. Silicon compounds, such as tetraethoxysilane, are frequently used for this purpose. Here, we present a time domain study of the sol-gel process using Dynasylan 40 with the addition of the nanoparticles of SiO2, Al2O3, TiO2 and CaCO3.

Compared to the traditional inorganic binders based on mortar or plaster, cementing clefts and cracks with polymer fl exible binders is effective in terms of better adhesion and fl exibility. Nevertheless, in order to be applicable in restoration practice they must comply with the condition of a minimum impact on the substrate, which frequently is a porous material. Silicon-based binders, synthetic rubber and hybrid binders based on silicone modifi ed with polyurethane and polyether were tested in this study. The binders were artifi cially aged under various conditions. At the same time, the study also focused on the extent of infl uencing of the porous cement substrate by the application of binders. The silicone binders showed the best resistance to artifi cial aging, however, the originally hydrophilic substrate became hydrophobic. Hybrid binders showed better resistance to moist rather than dry atmosphere. Testing in the QUV panel caused cracking and incoherence of all hybrid bonders. Various categories of binders showed similar properties in terms of resistance to aging and the extent of infl uencing of the porous substrate. The porous cement substrate was reported to be substantially infl uenced by all tested binders. Therefore, none of the tested binders can be unambiguously recommended for application in restoration practice.

Consolidants based on silica gel have been widely used for the consolidation of decaying monuments. Consolidants reinforce building materials by replacing cement that has decayed. However, silica gels are formed by polycondensation, during which process they shrink and may crack from the internal tension. Therefore, their lifetime is limited and the building materials have to be treated time and time again. In this study, we investigate whether silica nanoparticles are able to absorb the internal stress caused by gel solidification and, thereby, prevent crack propagation. We carried out a time domain study of the sol-gel process under a stable laboratory conditions.