Stone consolidation

Keywords Preservation of Historical Monuments / Stone Consolidants / Hydro-phobation / (3-Alkoxypropyl)triethoxysilanes / (3-AJkoxypropyl)-diethoxymethylsilanes... 

Summary In this paper, (3-alkoxypropyl)triethoxy- and (3-alkoxypropyl)diethoxy-methylsilanes are introduced as a possible basis for hydrophilic, elastic stone consolidants. The preparation of these compounds is described. Addition of (3-alkoxypropyl)diethoxymethylsilanes to commercial stone consolidants reduces the number of shrinking fissures of the resulting Si02-gel. Application of (3-alkoxypropyl)triethoxysilanes without any additives even offers the opportunity to produce hydrophilic, elastic consolidants for natural stones. 

We have investigated the application of ether-substituted triethoxy- and diethoxysilanes ((3-alkoxypropyl)triethoxy- (3-alkoxypropyl)diethoxymethylsilanes) for the preparation of hydrophilic, elastic stone consolidants. 

Fig. 1. Photographs of stone consolidants after polycondensation (a) unmodified stone consolidant (b) modified stone consolidant, elastificated with (3-methoxypropyl)diethoxymethylsilane (c) (3-methoxypropyl)triethoxysilane.

To investigate the elastic properties resulting from ether-functionalized silylester condensates, the diethoxymethyl derivatives were used in 1 1-mixtures with the commercial stone consolidant F510 of Remmers Bauchemie to prepare thick siloxane films in Petri dishes. Fig. lb shows a photograph of the polycondensate obtained from F510 modified with (3-methoxypropyl)diethoxymethylsilane. In comparison with the film produced by hydrolysis and condensation of the unmodified consolidant (Fig. la), considerably less shrinking fissures are observed. 

The ether-substituted triethoxysilanes were brought to polycondensation without addition of stone consolidants yielding films like the one shown in Fig. Ic for the polycondensate of (3-methoxypropyl)triethoxysilane which contains almost no shrinking fissures and therefore is very probably well suited as an elastic, nonhydrophobic consolidant. 

CaC03 in the form of calcite. Although biomineralisation has been observed for many years, the potential for its use in stone consolidation has only been explored relatively recently. Biocalcifying bacteria have been used to successfully promote carbonatogenesis on the surface of limestone buildings, statuary and monuments. This newly-formed carbonate is often resistant to mechanical stress, possibly due to the incorporation into crystals of organic molecules, produced as a result of bacterial metabolism. 

TABLE 13.4 Silane Stone Consolidation Products continued... 

Molecular aUcoxysilanes have also been used extensively in conservation and stone consolidation (Wheeler, 1992 Amoroso, 1983). They have been shown to suitably impregnate stone to significant depths (Price, 1975). Marschner reported (Marschner, 1978) that alkoxysilanes improved the resistance of sandstone to sodium sulfate crystallization. Some alkoxysilanes have been used in a treatment strategy combining the use of calcite coupling molecules to passivate the surfaces against new weathering (Drinker, 1998). 

Saka S. Wood-inorganic composites as prepared by the sol-gel process. In Wood and Cellulosic Chemistry, 2nd edition. New York Marcel Dekker, 2001, pp. 781-794 Satlla- L., Schuh H. Chronological development of stone consolidation on silicic acid ester base. Bautenschutz + Bausanierung, 1995 18(1) 77-81... 

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