In general the answer is yes, although there are some instances where priming is not necessary as explained below.
Priming of absorbent floors reduces the absorbency. This will increase the open time of the adhesive thus reducing the possibility of late placing. In addition, it will reduce the possibility of pin holing that can occur when smoothing compound is applied.
Priming of non absorbent subfloors with a suitable primer such as undiluted Stopgap P131 will act as an adhesive promoter for the smoothing compound.
Priming is not generally necessary when applying reactive adhesives such as polyurethane of epoxy systems.
Thursday, March 24, 2016