I have just posted a link for the lime paint on the general fresco forum:
http://www.battersbyornamental.com/wallerlime.htmThe best binder for lime and lime proof pigments is silicate based. I am very impressed with potassium silicate paints on plaster, concrete and lime mortar. They are cheap to make yourself, very durable, allow the surface to breath, and dry absolutely flat - like true fresco. The acrylic resins are just not working out anywhere where moisture and heat expansion and road vibration/surface movement is a factor. The acrylics also 'gum up' any mixture, so instead of the sensation of troweling 'ball bearings' - you have the sensation of trowelling sticky glue.
The silicate binders work so well because one of the secrets we have not revealed about true fresco is that the lime partially dissolves the silica sand to form calcium silicate. So adding another type of silicate (other than sodium silicate for some odd reason)is a natural mix for strength.This is also why white cement, another silicate, works so well with lime and sand. For a smooth 'plastic' surface a proportion of the dolomite and marble sands are better - they are softer and form more of a putty, not so soft to fall apart, but soft enough to self heal. I tried an experiment three years ago, ultramarine silicate paint on fresh white cement, lime putty and silica/dolomite sand - and after three years of snow, constant sun, frost and rain - it is still as bright and strong as the day I painted it.
Good 'sharp' sand is more important to fresco than lime, pozzolans (or what the trade calls 'fly ash)' is another very fine, sharp sand. Magnesium in lime, like calcium carbonate in paint, forms a useless filler powder, with no strength, but this only becomes a factor in freeze/thaw cycles, or constant running water, and is compensated for with the use of good sands.
Lets also not forget the country with more square metres of outdoor fresco than any other is Mexico - and the lime used were NOT European or even near as pure as contemporary North American limes, yet they are weathering extremely well. Although many of the pigments of Mexican fresco in the 20th century were imported from France through a store in Mexico City. The mayans and the aztecs were also painting fine quality lime stucco and fresco well before the Europeans. They too were very careful about the sands and the water used, and Diego Rivera and his master plasterer sought out the Mayan sources of materials in creating their magnicent frescoes.
Since we in North America love the numbers game - Rivera's series of 124 frescoes in the patio of the Public Education Ministry cover 1,585 sq. meters, or over 17,000 sq. ft.: the equivalent of a a painting one foot tall and over three miles long. This is just one of the many frescoes in Mexico, and one of many in Rivera's short career.
