The Rathgen Research Laboratory in Berlin is engaged in the restoration of monuments in two tropical countries, Sri Lanka, and Honduras. Both sites suffer from rapidly progressing stone decay, due to the chemical action of rain and the growth of microorganisms. Preservation techniques must stress protection against humidity. To that effect, coating walls with water-repellent materials must be considered as well as constructive interventions such as the installation of roofs. See also <i>AATA</i><b> 21-2111, 22-1267</b> and * 323-1552*1. -- AATA