Hi, can anyone pls suggest a suitable bonding agent to stick large marble travertine tiles (20mm thick) vertically to a pool wall lined with vinyl liner? The travertine will be supported from beneath by a concrete step taking much of the weight, so the glue / bonding agent will not need to support the (shear) weight of the marble...just needs to keep it attached to the wall. Pool is filled with chlorinated water and approx. 1/2 of the travertine will be below the water line. Grateful if anyone has any thoughts? I've added a photo showing the travertine patio and the vertical step with white & grey pool liner over which I want to stick the travertine. Thanks alot.