L. BINDA*, G. BARONIO*. *Politecnico di Milano
L. ANTI** and A. ANZANI** **Architects, Milan

Weathering of masonry materials in ancient buildings, occurs in ail European countries. It may be accelerated by pollution, but it is also frequently caused by lack of maintenance. Instead of replacement synthetic products may be used to impregnate the decayed material.
The efficacy and durability of the treatment depends on the physical and chemical properties of the product itself and of the masonry materials (porosity, strength, deformabitity). It is also expensive.
In laboratory tests the rates of deterioration of treated and untreated materials was measured by the loss of untreated material during repeated crystallization in sodium sulphate solution. The results showed that in some cases treatments can give adverse effects on durability. The procedure can be applied in-situ to measure the degradation connected with the loss of the material from external surfaces of walls.