In two videos on YouTube, Tamar guides viewers through 1: the making of natural plaster and 2: application of a natural plaster to a light straw-clay wall.

Her mix, in order, is:

• 3 parts sand
• 1 part manure
• 2 parts slaked clay (thick wet clay slurry)
• 0.5 part wheat paste (flour and water heated slowly until translucent, and then mixed in a blender with more water
• Mix, then add 1 part chopped straw at the end. I would add: Let the final mixture sit a while, covered, to let moisture to permeate the chopped straw.

She says the benefits of manure from grass-fed cattle are:

• lots of tiny undigested grass fibres, great for tensile strength
• enzymes, makes the plaster more durable, weather-resistant, reduces dusting of the sand on the plaster surface

Benefits of the wheat paste are:

• like manure, makes it more durable
• makes the plaster a little harder when dry

The more we can learn about the properties of these additives, the better. At best all we seem to have is anecdotal evidence of the properties that additives like manure, wheat paste, fermented yeast, and fermented straw, contribute to a plaster.