discussing sbr with another plasterer, he puts sbr in scratch coat mix as well as waterproofer,said he has had some problems with waterproofer not holding back enough and with sbr better all round, i emailed technical dept at cementone, and the reply was( waterproofer and sbr will entrain too much air and reduce density of mortar, could make the mortar weak and friable,thought i 'd pass the info on lads.