The reason that fresco is so difficult today is that the skills needed have been split by our modern world - plasterers are tradespeople, artists are usually painters. Fresco requires both. I would like now suggest there is another trade you have to know - lathing!

Lath is the secret to strong plaster and stucco cement. The old day walls were built thicker and thicker for strength, but this does not work, the Sistine Chapel proved that. Some sort of mesh, whether it is wood saplings and reeds, or high tech graphite fibre mesh, drastically improves the strength of the piece.

For fresco practise, I have been using expanded galvanized metal mesh lath, with 3/8" ribs running every four inches. It is called "Hy-Rib" and will be available from any stucco/plaster supplier. It may be difficult to get home, it is usually in 27" x 96" size, it can only roll up lengthwise. Cut out your panel sizes using tin snips, make sure you wear work gloves when cutting and handling. Place the pieces, "pointy side down" on a plastic covered table, do not worry too much if they twist and bend, the weight of the mortar should hold them down. Now fill the mesh with the mortar. I recommend adding white cement to the mortar for this "scratch coat" it is the backbone of the piece, you want it good and stiff for the next coats, and you cannot wait the long time that a 100% lime mortar will take to cure for "portable" panels. Still use lime putty as a "plasticizer"(to help work in the coarse sand with less water), and to improve "suction" (the ability of the piece to "pull" water through from the final coat and therefore working time). For small painting surfaces, like you describe, I add white cement at all coats, in lesser and lesser amounts, because I do not need the working time and I want to make absolutely sure the piece will stand up in a garden environment (up here in the Pacific Rainforest). I think my frescos could go in a swimming pool!

Just slightly "overfill" the lath by about 1/8",no metal should be showing, the plastic will stop it sticking to the table. Brush the surface to make it rough. If you are doing this
indoors, place a plastic bag over the piece(s)and wait a couple of days. You are now ready for the "brown coat" which is smooth with coarse sand (finer than scratch coat) and the "finishing coat" - in our case intonaco 100% lime putty and fine marble sand/dust. The nice thing about this technique is that you can prepare a whole bunch of mesh boards at once, wet them down the night before the brown coat, etc.

Once you get used to the lath technique, you can also make curves, or hang the lath on walls, ceilings, etc. The skilled plasterers apply the scratch coat to the lath using just enough pressure that the plaster "keys" through the back of the mesh. Whole rooms and whole buildings are constructed in this way and it has proven the test of time. Plasterers usually have the lathers come in ahead of time to do this work - so can a fresco artist if he/she is experienced with the plastering.

I hope this helps - it is not THE answer, you will find your own way with the materials and skills you have available in your area. If it seems like a lot of work, calculate how much $ per sq ft painting area you are getting compared to gesso canvas or watercolor paper and that fresco is beautiful interior or exterior.