Cast-in-place concrete typically has bug holes and voids on the surface as a result of pockets of air.  Plastermix is a cementitious parge coat applied in a thin coat to fill the voids and create a uniform surface.         

Mix 1 part K-88 Admix with 3 parts water to a slurry consistency.  Apply with a sponge float.  For a texture coat, apply with a trowel, allow to take up until thumbprint hard.  Apply a second coat with a trowel and finish with a sponge float.  Do not exceed 1/16".