A back-up apparatus for use with a surface treating apparatus can include a back-up plate having a pad attachment face and a back-up pad having a first pad face and a second pad face. The back-up apparatus can also include a porous interface layer. The interface layer can include an outer face. The back-up apparatus can also include a layer of a first adhesive on the outer face and extending into the interface layer, and a layer of a second adhesive provided on the layer of the first adhesive. The second adhesive can be selected to releasably adhesively bond to an abrasive sheet. The first and second adhesives can be selected such that the adhesive bond between the first adhesive and the second adhesive is stronger than the adhesive bond between the second adhesive and the abrasive sheet.