Challenging transient flooding effects on dampness in brick masonry in Venice by a new technique: the narthex in St. Marco Basilica

St. Marck\u2019s Basilica has always shown peculiar dampness problems, particularly caused by water seepage and rising moisture: this leads to continuous decay of the ancient brick masonries due to soluble salt migration and crystallisation in the pores of the material, efflorescence formation, freeze and thaw effects, chemical and biological attack, exterior erosion and so on. Considering the uniqueness of the internal wall and ceiling finishings (frescoes, mosaics, etc.), only non damaging and non disfiguring reclamation methods can be applied, which lead to the search for newer and newer anti-dampness materials and techniques. Furthermore, any anti-dampness system is required to be reversible, i. e. to be removed when desired. Since 1998 some brick masonry of the narthex of St. Marco in Venice has been subject to experimentation to reduce/eliminate rising dampness. This has included a new, simple and fully reversible technique based on spontaneous and automatic governing of the electrokinetic phenomena arising from water migration in porous building brickworks. This method does not require any external energy supply or controlling apparatus and has been successfully tested in several ancient buildings against rising dampness (e. g., San Luca baroque Porticoes in Bologna, XIX Cent. Church of Blessed Crucifix of the monumental Cemetery of Ravenna (Italy), baroque Church of St. Caterina of Italy in La Valletta (Malta), and others). Experimental with the self-polarising method based upon the insertion of conducting (steel) bars (if properly configured and placed) showed to be very helpful, ensuring at the same time reversibility, self-regulation operation without any external power supply, possible structural reinforcement of the brick masonry (when needed) and absence of the architectural image changes and/or losses