performance it will be obvious to one of skill in the art that while it is desirable to employ materials which afford low viscosity solutions usually associated with low molecular weight or non polymeric materials the materials so employed cannot be of such low molecular weight that they evaporate from the stone surface until the discovery of the method of the present invention all materials in the art employed for application to stone for the purpose of preservation have been polymeric it is further preferred that polar groups such as urethanes should be present in the coating material to promote adhesion of the coating material to the stone surface and decrease the tendency of the coating material to continually penetrate to the interior of the stone and reducing surface efficacy in terms of liquid water repellency esters amides and u2014 ch 2 cf 2 u2014 moieties are examples of other such adhesion promoting polar groups while according to the method of the present invention it is possible to apply the urethane to the stone in neat chemical form using methods such as are known in the art such as painting or spraying it is preferred to dissolve the urethane in a solvent which acts as a volatile diluent in the spraying operation to.