This study compares the consolidation efficiency and compatibility of three selected alkoxysilanes on two porous carbonate and silicate substrates. Emphasis was given to artificially induced microstructural defects and subsequent restoration of mechanical and physical properties. Two newly engineered formulations (1) a TiO₂ modified tetraethyl-orthosilicate in isopropanol with 70% active content and (2) a TiO₂ modified alkyl-trialkoxysilane in isopropanol with 75% active content were compared to a commercial product (3), a solvent free tetraethyl-orthosilicate with 99% active content. Treatments were evaluated by scanning electron microscopy, mercury intrusion porosimetry, colour impact and their effect on dynamic modulus of elasticity, splitting tensile- and flexural strengths, capillary water absorption and water vapour permeability. A key outcome was that mechanical strength gain induced by treatments is primarily governed by a stone’s texture and microstructure, and secondarily by the gel deposition rate of consolidants. Likewise, the kinetics of the gel-forming reaction during curing is dependent not only on the product but also on the substrate. Therefore, the moisture related properties and the visual impact develop during time. There is no general trend on how it evolves in time, which can lead to incorrect interpretations of treatment compatibility. The results prove that wide-ranging treatment performance is obtained when applying the same products on different substrates.

A nano-silica consolidant and nano-titania modified tetraethyl-orthosilicate were applied on two building stones, a carbonate and a silicate, by brush, poultice or capillary absorption. Neutron radiography was used to monitor capillary water absorption, and to analyse changes in physical properties caused by heat treatment of specimens for the purposes of artificially ageing and different treatment applications with stone consolidants. Moreover, ultrasonic pulse velocity and gravimetrically determined water absorption were analysed to cross-validate neutron radiography. The results reveal that reactive systems like tetraethyl-orthosilicates need an unknown period for polymerisation, which makes nano-silica consolidants more favourable for construction follow-up work. While polymerisation is incomplete, hydrophobic behaviour, water trapping and pore clogging are evident. Within the tetraethyl-orthosilicate treatment, poultice and brushing are strongly influenced by the applicant, which results in wide ranging amounts of water absorbed and anomalous water distributions and kinetics. The carbonate lithotype displays polymerisation initiated in the core of the specimen, while the lateral surfaces are still mostly hydrophobic. Reaction time differences can be attributed to the different amounts of consolidants applied, which is a result of the chosen application settings. Artificial ageing of stone specimens is a prerequisite when mechanical strength gain is studied, as demonstrated by sound speed propagation.

The interdisciplinary project Stone Monuments and Stone Quarrying in the Carnuntum - Vindobona Area aims to acquire new knowledge about Roman economic