If im honest i prefur to use polymer based bonding agents, the wickes one can be skimmed in two hours where BGs thistle bond it have to be left 24 hours before skimming , money does allways come into the picture with most customers and bonding agents cost a lot more than pva but i allways offer the costomer a choice , if you do go down the bonding agent route seal the walls first with artex stablex then go over again with wba you dont have to wait for the stablex to dry fully . WBA cost about £13 and will do 11-15 sqm per tub , bond it cost around £35 for 10ltrs not sure what the coverage is on that ?