If you have done any waterproofing coating of RCC then you need to protect it. So, hacking (tancha) is not a good option. You may go for some type of bonding agent (to be applied just before plaster).
In market lots of bonding agents are available i.e. latex based.
I have used one type of bonding agent when we were doing Gypsum Plaster (I have forgot the type & brand name, but u can search in market). That bonding agent comes with some coarser sand which sticks on the surface when you apply bonding agent on RCC surface, it also helps to give mechanical bonding.