This report arises from a conservation intervention on two walls - one of mudbrick and one of fired brick - laid in clay. The work was carried out in situ during the excavation campaigns for the Crypta Balbi in Rome. To explain something of the background: the Crypta Balbi excavation involves an urban area in the center of Rome, in a zone that over the past two millennia has experienced a continuous superimposition of human activity. Thus today it presents an exceptionally interesting historical stratification.