We have had some mold appear on the surface of a few areas of walls using fat plaster. After completely drying, it easily brushed off, never to appear again. It was probably due to a lack of ventilation during the curing process. Since the presence of the organic fiber makes the plaster most susceptible to mold, the fiber can be omitted from the second coat application and used only in the first lath chinking coat. For walls that you intend to cover with milk paint, the finish will be smoother if the final surface is fiber-free. For the second stage cover coat, consider using a low-fat or fat-free plaster.
Omit any fiber and increase the sand ratio until the plaster dries without cracking. Experiment with the amount of flour paste, too. A fiber-free sand-rich earthen plaster is less apt to have mold problems. The mix works best when it is firm yet malleable and a little sticky. If there is adequate sand mixed with a stable, low-shrinking clay, even a thick fiber-free plaster will dry without cracking. Well-graded coarse, sharp sand is a prerequisite for success.
15.5: Fiber-free plaster goes on quickly, and deeply fills all the voids between the rows of bags until the plaster comes flush with the wire.
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