This study investigates the dimensional response to environmental changes and the physical reasons for the development of deformations of modern paintings on fibre board supports. Dimensional changes were monitored with photogrammetry during humidification treatments. Thereby the penetration depth of moisture and the swelling of different organic polymer films can be related to the response of the support. It has been found that micropores and crazing, resulting from the first stage of the drying process of oil paint, can lead to visible cracks, because the moisture absorption of the paper based support is so rapid that the paint layers cannot accommodate the dimensional changes. Also, osmotic blistering can appear in young acrylic resin paint layers. This knowledge forces us to evaluate much more carefully the influence of moisture and its consequences on paint layers on board. The investigations clarify the dangers which can arise from humidification treatments, and suggest that a very slow and gradual increase of relative humidity in stages to a certain limit can reduce the risk of damage to the painting.