Mixing Sand, Cement and Bonding?

I've got an uneven wall surface one one side of a fireplace opening that I need to build up to tile on. In some places the difference must be 2-3 inches.

Its been suggested to me (by the stove installer) that I build this up using a mixture of sand, cement and bonding (to make it really sticky), before rendering, but I've never used these together before (i.e. only sand & cement or only bonding).

Can this be done and if so what mix should I use?

don't mix plaster with cement. the sulphates attack cement. moisture makes it expand and crack. you can add a little PVA to sand and cement to make it sticky (it will also stick permanently to your fingernails)

instructions s/b on the PVA tub.