The degradation and alteration of stone in buildings and monuments are often far advanced when it is decided to take action. To avoid complete disintegration, it is necessary to use pro-tective and consolidating treatments, even though they sometimes imply certain risks. Since water is the principal agent in the process of decay, protective techniques must be effective against water. The type of stone studied is a quartz-feldspar calcareous sandstone, particularly vulnerable to the effects of different weathering agents. Acrylic resin was selected for the treatment, because of its high transparency and good aging properties and it is appropriate for outdoor applications. -- AATA