To extend the lifetime of wall-paintings in the Mogao Grottoes, various kinds of conservation materials (for example, PVA, acrylic acid and B72) and techniques (for example, adhesion, consolidation and surface coating) have been used in the past decades. However, as a basic concern, it still remains obscured how the deterioration mechanism of wall-paintings changes after conservation materials are applied. In this contribution, an assumption was advanced to clarify this mechanism. Different layers in the wall-paintings have different physical properties, such as thermal and moisture expansions, which may be altered after the conservation materials penetrate into the paintings. The differences of these properties may cause stress between the layers in the paintings with the change of environmental factors, which will finally lead to deterioration of wall-paintings. A series of experiments were performed to determine thermal and moisture expansion properties of consolidated wall-painting plasters. The impact of the conservation materials on the expansion properties of wall-painting plasters was quantified, in order to evaluate these materials. Consistency of experimental conclusions and conservation experience validated this hypothetical mechanism.
