Clay poultices in salt extraction from ornamental stones: A statistical approach

The extraction of salts by layered (bentonite) and fibrous (sepiolite) clay poultices from stone materials currently used in Heritage buildings was st udied. Analyses were performed on stones affected by salts but not submitte d to humidity, and also on stones affected by salts and simultaneously subm itted to continuous or intermittent humidity during the salt-extraction pro cess. From the experimental results and the statistical analysis, the appli cation of two successive poultices is sufficient for an efficient extractio n of Cl- and NO3- in the absence of humidity. However, under humid conditio ns, the efficiency of the method is reduced considerably. For SO42-. the us e of hydrotalcites (anionic clays) is recommended for more effective extrac tion.