Marble is a material for which until now no convincing solution for surface protection has been found. To protect a marble object from weathering, it is necessary to analyze the causes of decay in order to elaborate conservation techniques which counteract most of the destructive forces. The action of bacteria or the growth of lichens can be stopped, constructive failures can be repaired. But a convincing consolidation of a decaying marble is hindered by its low porosity and the danger of the formation of superficial crusts, when impregnated with less fluid consolidants. The use of solutions of acrylic resins by brushing or by vacuum impregnation competes with the use of ethyl silicate and observation over a long period will reveal which method is the safest. A suitable and repeated hydrophobing of the surface in any case is necessary to prevent an attack by humidity.