Constraints of the durability of inorganic and organic consolidants for marble

In the present study, 5 different consolidants were tested on 5 different marble varieties preliminarily subjected to artificial weathering, to evaluate their consolidating effectiveness and thermal behavior after consolidation, in terms of residual strain after heating–cooling cycles in dry and wet condition and tendency to bowing. Treatments based on ethyl silicate, with and without a coupling agent to improve the performance on calcitic substrates, exhibited modest increases in cohesion after consolidation, as well as an increase in the thermal expansion coefficient and some residual strain at the end of the cycles. Paraloid B72 caused minor alterations in the pore system and limited increases in ultrasonic velocity, while the so-called “acrylic total impregnation” method led to an almost complete pore filling and significant improvements in cohesion. While the latter samples apparently resisted well to heating–cooling cycles, samples impregnated with Paraloid B72 exhibited progressive collapse of the fabric, likely due to the low glass transition temperature of Paraloid B72. Ammonium phosphate proved to be able to significantly improve marble cohesion and led to lower residual strain after heating–cooling cycles, compared to untreated marble. The DAP-treatment also exhibited a significant ability to slow down further bowing of already bowed slabs and to prevent bowing of initially planar slabs.