A new portable technique to evaluate the compatibility of protective treatments applied on monumental stones

An efficient protection implies an optimal condition not only against the water inlet but also for the water outlet through evaporation. The compatibility of a treatment involves three main aspects: aesthetical, physical and chemical. In the paper the physical aspect was mainly considered, focusing on the characterization of one compatibility parameter: the Water Vapour Permeability (WVP). This parameter is determined in laboratory with the "cup method" in agreement with UNI EN 15803:2010, while does not exist a correspondent on site technique. In the paper is proposed a new metodology: "Contact Bag" (CB), for the estimation of the WVP both in lab and on site. The CB allows to easily determine the amount in weight of the water evaporated by a stone surface in 24 hours. The special plastic bag, containing a known amount of silica gel, is applied on a stone surface with an adhesive and sealing material for different time intervals. The silica gel forces and traps the water vapour present into the stone. The most reliable results have been obtained with a contact time of 24 h. The method has been validated in laboratory on Lecce limestone specimens, comparing the CB values with those obtained with the standard dry cup method (UNI EN 15803:2010). The experimental results, using the new methodology, are in agreement with the standard method. The compatibility of the protective treatment made with Fluoline HY has been evaluated either on Lecce limestone and on specimen of Gioia marble, Portland limestone, Monte Senario sandstone and Portland Cement 42.5R.