ilia, thank you for those very valuable tips.
I've red with attention the albuquerque fresco workshop "report" on your site, you insist on angular sand as opposed to round sand, it seems that the only sand I can get here is round, ocean sand but washed and sterilized, guarantied without salt, I'm wondering if this sand would allow me to do a decent plaster.
I am also wondering if the cement can be incorporated in the putty many days in advance, if is has the same capacity as lime, to remain moist and workable after a week in a air proof bucket.
In other words, is it possible to mix all the ingredients in advance includind Portland cement?