Hi Carlos
This is one area that I can help in
Your plaster mixture if you are looking for the historical mixture is 3 shovels of sand and 1 of slacked lime. You would use this for the scratch coat (first coat) also if you do not have hair to mix into the mixture as a binder, you can use hemp just take manila rope on a wooden horse and and axe and cut short pieces 1 to 2 inches long it will resemble hair in the mixture, and will provide the keys with strength.
The next layer would be the above mixture without the binding agent, and this layer was usually the levelling layer and would begin the process of smoothing up the wall and removing any irregularities. Please scratch the surface very lightly only
The third and final layer is usually just a thin layer of the putty lime mixture, (sometimes a hardening agent is introduced) This layer is trowelled with a steel trowel and should ring out like a bell and be smooth enough to be shiny after hardening.
We sometimes used just river sand for the sand part of the mixture free from organic contamination or pebbles or stones.
I hope this helps you out. the whole thing isnt as easy as I make it out to be, but if you are handy with a trowel and a float you can master it. Another idea is to make a small mockup of wall complete with wood lath and experiment before going to a larger surface
good luck
NH
