The most important results of a large number of tests looking at external plastering on brick masonry are presented. The tests confirmed that not only present-day standard external walling bricks but also thermally optimised bricks with lightweight plaster undercoats according to DIN 18550-4 can be used for simple, safe and economical plastering. Characteristic properties of the bricks are described, including cross-section, plane parallelism, bulk density (brick and ceramic body), perforation volume, compressive strength, tensile strength and elastic modulus of the ceramic body, and shear strength. The production of the lightweight plasters and selected material properties are also described. 8 refs.