A short step-by-step for portable fresco painting:
Portable frescoes can be completed on any rigid surface containing enough texture to hold plaster. In this case I used 3/4" plywood. The black roll is roofing paper used to protect the wood from the wet plaster.
Plaster will not stick to wooden or smooth surfaces so I have fastened expanded metal lath to give it a suitable "grip".
Application of the "scratch coat" mixed from one part lime putty, one part grey portland cement and 2.5 parts of coarse sand aggregate.
"Scratches" are added at the end when the plaster is somewhat firm. Similar to the expanded metal lath, this provides a proper tooth for the subsequent middle layer.
Wetting the dried scratch coat before applying the next layer is needed to keep the top layer's moisture from wicking out to the bottom layer. This prevents cracking and also makes spreading much easier.
This image shows the third and final coat of plaster commonly called the intonaco. It is made up of 3/4 part lime putty to one part fine marbled dust.
Note: The second coat was not photographed but contained a layer made from one part lime putty and two parts medium sized sand. Although only one layer of plaster is needed to paint a fresco (not uncommon) additional layers help increase the strength of the plaster, helping to reduce cracking. Three coats have proven to be stronger then two etc etc.
Before painting begins and as soon as the intonaco is firm enough to withstand impressions from a finger tip, the surface is polished with a clean damp trowel. This helps smooth the plaster if desired and the compression brings lime to the surface.
A finished buon fresco (3'x2') "Michelle Affresco"
A brief history of fresco painting: (coming soon!)
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