Fresco Plaster Coats
"Fresco Painting is only as good as the plaster it is put on. It is impossible to paint a buon fresco without clear understanding of plaster and it's properties.
Improper plaster will reject paint - there are NO shortcuts in fresco!"
Fresco Plaster Coats are made of high calcium
and "aggregate" which, most commonly is washed river sand, marble meal, volcanic tuff or the combination of it. The proportion of the mortar or plaster mix generally is:
1 part lime putty : 2 parts aggregate (sand)
5 parts lime putty : 8 parts aggregate (sand)
Washed River Sand is the best aggregate for making a fresco plaster, it is clean from impurities such as silica, dust, clay, organic particles, and the biggest enemy of all plasters - SALTs. This sand is also most likely to be of a right angular shape needed for "proper interlocking".
Traditionally there are five distinctive fresco plaster coats (from last to first):
1. Intonaco or Skim Coat - final plaster coat on wich the actual painting is done.
2. Arriccio or Brown Coat - smooth, sand finish coat on which intonaco is applied.
3. Float Coat - smooth plaster coat, base for arriccio coat. This coat is fine leveled and floated with darby and large wooden float. Usually this would be a "conventional" stucco finish installed by plastering contractor.
4. Rough Coat - rough plaster coat made with somewhat coarse sand. This coat is often combined with float coat by conventional plastering contractors.
5. Scratch Coat - the initial and one of the most important coats. This coat is applied directly to wire mash or wooden lath and then scratched with "tooth edged" trowel. Cement is often added to this coat for hard and fast setting.
Mortar for fresco plaster coats is mixed differently then for conventional plastering. In preparation of the mortar for fresco painting only high calcium lime putties and traditional mixing methods are used.
To be exact, conventional plastering has moved from calcium based lime putties to magnesium based hydrated limes in powder form which altered the technique of mixing mortar.
The main "alteration", difference is that traditionally, aggregate (sand) is added to lime putty and mixed together until the resulting mortar gains plasticity and no "dry" sand lumps are present.
In preparation of mortar for modern day outdoor stucco or interior plaster magnesium enhanced hydrated, dry, lime is mixed with sand and water added as needed in much larger amounts then it is suitable for fresco plaster. Excess of water makes mixing easier. Also due to high magnesium content resulting mortar sets much faster, which is very convinient for construction but absolutely futile for fresco painting.
"Buon Fresco Foundations" - Fresco Plaster DVD video introduces the student to foundational principles and techniques of the preparation and application of slaked lime plaster for True (Buon) Fresco Painting. Topics illustrated include the step-by-step process of plaster preparation filmed in real time without omissions. A student will be able to see exactly how long each step takes and what tools and methods each requires. iLia Anossov (fresco) guides the student by a thorough and clear demonstration of the foundations of calcium fresco plastering relevant to any size fresco.
Buon Fresco Foundations: FRESCO PLASTER
Copyright 2005++ iLia Anossov & Fresco School