PVA adhesive is useful in many scenarios in which you apply a certain coating to an existing surface. It helps the surface remain workable while you skim it for a longer time because the PVA adhesive prevents the coating over it from drying too quickly. PVA glue or adhesive also allows for a stronger and longer-lasting bond between the existing surface and the coating you apply. One such use is the preparation for the application of plaster on top of a skimmed mortar structure.
Mix two parts PVA glue with one part water in a bucket.
Dip a paint roller into your mixture and allow it to absorb some of the PVA mix.
Paint a coat of PVA glue mixture evenly on your applied mortar. Allow the mixture to dry. You know when PVA glue dries when it is no longer white.
Wash your paint roller in a tub or bucket of water. Do this repeatedly, replacing the water with a new batch of clean water every time until no more glue mixture dilutes away from your roller.