Hi Karla
An expanded mesh fixed to 6mm plywood is very good basis for small frescoes (Up to about 60cm x 60cm). Apply 1cm thick browncoat and after two days (local Weather) apply 2nd coat of about 1/2cm thick. The next day go ahead with Intonaco and pigments. You maight not get the typical glazed film over your dried up work but you will have all the rest: beautiful piece of buon fresco, true feeling of working with lime-sand-pigments and a simple way of doing it. For exercises you can work also with only two coats, browncoat and Intonaco. If you keep your mortar free of cement you can store it "forever" in aplastic bag + mix it with newly made mortar when ever needed. Good luck.

Yoram