The Rathgen Research Laboratory has conserved historical buildings in several countries with tropical or desert climates. In the tropical climate, weathering is due to an intense growth of vegetation, to a chemical decomposition of the stone and to the condensation of water in the interior of buildings. In arid climates the action of salts and the influence of changing temperatures contribute most to the decay of stone. In both regions much decay is due to theuse of the monuments for religious purposes or as a tourist attraction. -- AATA