There are two fundamental reasons paint tends to chip and flake off of plaster. First, because plaster takes a long time to cure, you must wait a specific period of time before you paint, or you will have no chance at paint adhesion. In addition, because plaster is so dry, it tends to absorb the water from paint, which can lead to a breakdown in the paint's adhesive qualities. You can sidestep each of these problems by using the proper preparation and application techniques.
Wait three months for the plaster to cure before applying any primer or paint.
Cover any areas you do not want painted with painter's tape. Cover flooring with plastic dust sheets. Lay heavy-duty fabric dust sheets on top of the plastic.
Dilute the latex primer by mixing in 1 cup of water to every 1 gallon of paint. Stir for five minutes using a wooden stir stick.
Apply the diluted primer to the plaster using a roller. Roll vertically, moving slowly to prevent splattering. Smooth any runs or drips with the roller. Allow the primer to dry for four full hours.
Clean all painting tools with water.
Dilute the latex paint just as you did the primer. Apply three coats of the diluted acrylic latex to the primed plaster in the same manner as you did the diluted primer. Allow three hours of dry time between each coat.
Apply thin coats. Do not attempt to cover the plaster in only one or two coats as this will lead to runs and drips. Thinned paint tends to flitter and spatter. Be sure to take your time and meticulously cover flooring and areas adjacent to the plaster, or you may end up with a mess.
Thinned paint will pool on plastic dust sheets and soak through fabric ones. Be sure to use the two types of dust sheets to prevent unnecessary messes.