Advanced mortar coatings for cultural heritage protection. Durability towards prolonged UV and outdoor exposure

Abstract

In the present work, two kinds of hybrid polymeric-inorganic coatings containing TiO or SiO particles and prepared starting from two commercial resins (Alpha®SI30 and Bluesil®BP9710) were developed and applied to two kinds of mortars (an air-hardening calcic lime mortar [ALM] and a natural hydraulic lime mortar [HLM]) to achieve better performances in terms of water repellence and consequently damage resistance. The two pure commercial resins were also applied for comparison purposes. Properties of the coated materials and their performance were studied using different techniques such as contact angle measurements, capillary absorption test, mercury intrusion porosimetry, surface free energy, colorimetric measurements and water vapour permeability tests. Tests were also performed to determine the weathering effects on both the commercial and the hybrid coatings in order to study their durability. Thus, exposures to UV radiation, to UV radiation/condensed water cycles and to a real polluted atmospheric environment have been performed. The effectiveness of the hybrid SiO based coating was demonstrated, especially in the case of the HLM mortar.

Superhydrophobic Coatings Based on Siloxane Resin and Calcium Hydroxide Nanoparticles for Marble Protection

“…The latter is responsible for the extreme wetting properties, which are discussed in the next paragraphs. The scenario revealed in Figure 2 for the siloxane+Ca(OH)2 coatings follows the results reported previously for the effect of SiO2 nanoparticles on the surface structure of siloxanebased composite coatings [6][7][8][9][10][11][12][13][14][15][16][17]. Surface structures reported for siloxane+SiO2 coatings on marble [6][7][8][9][10][11][12][13][14][15][16][17] are similar to those shown in Figure 2 for the siloxane+Ca(OH) 2 coatings.…”

“…In these early works, silica (SiO 2 ) nanoparticles were used as additives to roughen the surface of siloxane, acrylic, and perfluorinated polymer coatings [6][7][8]. Since then, SiO 2 nanoparticles have become the standard additives for the production of superhydrophobic polymer+nanoparticle composite coatings for natural stone protection [9][10][11][12][13][14][15][16][17]. Other nanoparticles, selected for the same purpose, are aluminum oxide (Al 2 O 3 ) [8] and tin oxide (SnO 2 ) [8], as well as photo-catalytic and biocidal nanomaterials, such as titanium oxide (TiO 2 ) [8,13,[18][19][20][21], zinc oxide (ZnO) [12,19], and silver (Ag) [22].…”

“…Nanoparticles of Ca(OH) 2 are produced, characterized, mixed with a siloxane-based precursor in various concentrations, and sprayed onto marble specimens to evaluate the wettabilities of the produced composite coatings. For comparative purposes, other composite coatings were prepared using the standard SiO 2 nanoparticles that were utilized in the past to achieve extreme wetting properties [6][7][8][9][10][11][12][13][14][15][16][17].…”

Performances and Coating Morphology of a Siloxane-Based Hydrophobic Product Applied in Different Concentrations on a Highly Porous Stone

“…After the application of the WR solutions, reductions were measured for all the water vapour transport parameters (Table 3). The obtained results are comparable to those reported in the literature for siloxane-based coatings on stone materials [15,34,[47][48][49]. The permeability decrease, RVP, remained below the threshold of 20%, usually accepted as tolerable [50] (p. 540), only for the T 2.5 samples.…”

“…These materials most often are obtained from acrylic, fluorinated, and silicon-based monomers. Among them, polysiloxanes, and their precursors, the silanes, have been frequently used [6][7][8][9][10] and have also recently been proposed as nano-composites by introducing nano-particles of inorganic oxides into hybrid siloxane or silicone polymers [11][12][13][14][15].…”