POLYMER TREATMENTS FOR STONE CONSERVATION: METHODS FOR EVALUATING PENETRATION DEPTH
FRANCESCA CASADIO, & LUCIA TONIOLO
2.1 STONE SPECIMENS
The project focused on lithotypes of varying porosity, widely occurring in historic architecture and monuments in Italy. In particular, results are reported regarding substrates listed below:
- Noto stone, a highly porous calcareous stone with total open porosity ranging from 25% to 35%, widely present in the historic architecture of the famous baroque town of Noto, near Syracuse, Sicily.
- Yellow Angera stone, a Triassic dolomitic sedimentary rock containing trace amounts of clay and iron hydroxide (responsible for the yellow color), characterized by 11.5% total open porosity, widely present in structures in Lombardy.
- Candoglia marble, a metamorphic, compact calcareous stone characterized on average by 1% total open porosity, largely employed in building and sculpture: it is the construction material of the Cathedral of Milan (14th‐19th century).
2.2 POLYMER TREATMENTS
The resins used for treatment of the stone specimens were:
- Paraloid B-72 (Rohm & Haas), ethylmethacrylate/methylacrylate copolymer
- TFEMA/MA, a partially fluorinated, experimental, 2,2,2 trifluoroethylmethacrylate/methylacry-late copolymer (Ciardelli et al. 2000), basically a fluorinated homologue of Paraloid B-72;
- Wacker 290 (Wacker Chemie), a water repellent based on oligomeric alkylalkoxysiloxanes.
Details concerning these polymers' characteristics (including molecular weights and glass transition temperatures [Tg]), efficacy, and UV resistance are reported elsewhere (De Witte et al. 1993; Melo et al. 1999; Chiantore and Lazzari 2000; Alessandrini et al. 2000a, 2000b).