Metodologie di consolidamento di superfici architettoniche interessate da sali solubili. Il caso di studio delle fortificazioni maltesi : valutazione dell’efficacia dei trattamenti e criticita’

Abstract

Soft limestones used as building materials in marine environment undergo fast and peculiar deterioration processes that seriously damage the historical and architectural cultural heritage of Mediterranean cities. Presence of soluble salts in masonry is one of the most significant cause of degradation for highly porous stone and can limit the efficacy of adopted conservation treatments. Organic and inorganic consolidation methods, already evaluated in laboratory on Globigerina Limestone (the local limestone of the Maltese islands) quarry samples, were tested on deteriorated stone of local sea-side fortifications (Lower Barrakka Garden bastions). Evaluation of masonry salts content was performed by IC before treatments: chlorides, nitrates and sulphates were found into porosities of substrates. Barium hydroxide, Ba(OH)2·8H2O, ammonium oxalate, (NH4)2·(COO)2·H2O, and dispersion of calcium hydroxide, Ca(OH)2, in alcoholic medium were tested in comparison with ethyl silicate, acryl-siliconic resin and fluorinated products. Efficacy of consolidation treatments was investigated by means of colorimetric measurement, contact sponge method to asses water absorption by capillarity and tape test to study surface re-aggregating properties.