Hydrophobic treatments for stone conservation - Influence of the application method on penetration, distribution and efficency

The performance of a water-repellent treatment applied to a stone surface is generally evaluated without considering the depth of penetration and uniformity of distribution of the active product in the treated porous material. Magnetic resonance imaging (MRI), a non-destructive methodology, has recently made it possible to visualize the presence and distribution of different hydrophobic polymers in rocks, thanks to their water-repellent properties, The authors show, through the use of this technique, how the penetration depth and the distribution of a water-repellent material in a stone are affected, and therefore may to some extent be directed, by the application method. Two commercial hydrophobic polymers (Paraloid B-72 and Silirain 50) frequently used in the restoration/conservation of stone artifacts have been tested on a biocalcarenite (pietra di Lecce).