After presenting several methods to simulate the weathering of building stones in the open air, an attempt is made to compare the mode of action of artificial and natural weathering on lime plasters using a number of characteristics. Plasters of the same composition are used, some of which were exposed to urban atmospheric pollution in a weathering device. The other specimens were placed in chambers and were attacked there by air enriched with 15 ppm of SO₂. To determine the degree of weathering characteristics such as SO₃ content, sulphate/sulphite ratio and abrasion behavior showed themselves to be suitable. The greatly differing results, revealed in these tests demonstrates that, under the conditions selected for the artificial weathering, a greater correspondence in the behavior of naturally and artificially weathered plasters can be determined only in exceptional cases, because many continually changing parameters, such as the SO₂ emission or the climatic conditions, cannot be simulated completely during testing. In addition the time factor exerts a major influence. Although doubts about the usefulness of artificial weathering have been expressed by some authors, the test results obtained encourage one to state that artificial weathering methods permit a relative evaluation of the weathering behavior.