old factory wall internal, making good, old sand cement haggled and falling off wall, area 4 seperate patches of aprox 5 square meters by 50mm thick, i was going to use cement lime sand 1:2:9 and plastercisor, and finish off with multi finish plaster. wondering if i could use ready mixed white lime morter 4:1 and just add 1 ratio of cement, does this make sence ? then a week later plaster with multi finish :-\