The consolidation of porous stones using ethyl silicate has a long-term practice in thefield of conservation. In the present study three Neogene porous building stones (a limestone, a volcanictuff, and a calcareous sandstone) from Hungary were selected and consolidated with ethyl silicateusing a vacuum-circulation (VAC) method. Drilling core samples taken from the test blocks were investigatedby different microscopic methods, such as polarising microscopy, cathodoluminescence microscopy,and scanning electron microscopy. Based on the observations it can be stated that especiallythe cathodoluminescence and scanning electron microscopy are eligible for an exact and unambiguous2- and 3-dimensional visualisation of the amorphous solid consolidant in the pore space of the stone.The results have shown that the distribution of large gel fragments with shrinkage cracks is different,irregular, and mostly limited to the sub-surface zones in all three stone types. The results of the microscopicobservations were compared to drill resistance and ultrasound transmission velocity data, resultingfrom the measurements carried out before and after the consolidation. The preliminary comparisonhas not shown clear correlation between the optical observations and the values of mechanical measurements.The results thus suggest that changes in bulk mechanical properties after the treatment do notnecessarily correlate with the real places of precipitation and especially with the binding capacity of theconsolidant.

Key words: consolidant, visualisation, microscopic methods, porous stones, silica gel