Answer: hydrophobic coating called TECNADIS
According to gizmag.com, TECNADIS is made by suspending nanoparticles in a liquid carrier (the identity of those particles is a trade secret). When applied to such materials as concrete, ceramic, brick, stone or wood, the coating causes any liquid subsequently applied to them to bead up and roll off instead of soaking in. Because it doesn’t completely seal their pores, air can still pass in and out, which minimizes moisture retention-related problems like mold.
