Vicenza and Indiana limestones treated with an acrylic-silicone resin mixture were studied to determine the behavior of the impregnant. The specimens were studied before treatment, after treatment, and after simulated aging in the laboratory. Water imbibition and the water absorption coefficient decrease after the application of the treatment. The open porosity decreases somewhat, especially for the larger pores, but does not change significantly even after licone resin (which is aging. Scanning electron microscopy examination of the samples shows that the mixture provides a fairly uniform coating on the stone particles. After aging, the silicone resin (which is a prepolymerized methyl alkoxy silane) polymerizes further and forms a network that holds the covered particles together. See also AATA 14-479 for related study.