When realizing fresco, a true fresco is painted into wet plaster creating a chemical bond between the lime/pigment mixture and the plaster. This method requires incredible stamina and a significant discipline.
A cheat or a faux fresco, if you will, is painting on dry plaster. This method is Secco or Fresco secco or dry fresco. Mix dry crushed pigment with egg white or egg yolk, or animal glue ore, or adhesive like casein or gum arabic establishing a tempera type medium. Make certain that your medium is more on the thin side. Remember, in traditional fresco painting, we glaze layer upon layer of pigment to establish a more saturated image.
To begin with, your wall will have been plastered and cured for a few days to a week. You can continue with a couple of possibilities.
One method is to prime your wall and base coat with an acrylic base paint. Paint two coats. Allow the wall to cure over night. Next forming a glaze out of an oil base, rub with a cotton non-linting rag in a circular motion to create the ground for your mural. Fold your rag in your hand tucking all edges inside the ball of the rag. Dab a little bit of glaze onto your rag. In a circular motion, rub the glaze onto the wall. Work in sections approximately 3 to 4 feet square. Within these sections, randomly add glaze and continue to render in a circular motion. Blend the edges of one circle into the edges of another. Be light on the touch and patiently move across the wall section by section. The result will be a soft glowing effect resembling that of a soft color wash.... Allow the wall to cure then paint your images with the above medium (the tempura type mixture) or simply a variety of glazes. You always have the option to either varnish or wax the wall once it has fully cured. The last finish is to seal the work and offer a simulated finish as seen in traditional frescoes.
Remember, in faux finishing, there is no definitive method for doing anything. It is always an innovative approach for replicating the real.