priming

Howdy All, I'm doing a remodel on an apartment building with concrete ceilings. I am looking for a product that I can prime the concrete with and then use hot mud to level out the ceiling. Any advice would be appreciated.

Client has a concrete balcony coated with Vulkem 350, a waterproof, wear resistant product that dries to a flexible rubbery finish. The balcony faces south in Raleigh, NC, and I imagine that anything I try to put on it will crack from the thermal stress, if it sticks at all. The ultimate goal...