Fillers

And to prevent the lime from shrinking and cracking, filler should be added.

Sand

• Fossil - has various impurities: clay, clays, iron salts - undesirable components in the fresco technique.
• River sand - is washed, the grains are clean, suitable for use. However, these grains are too smooth, which reduces their binding force with lime and gives the mortar a certain porosity.

Fossil sand is not round and therefore binds better. It just needs to be washed well.
Oily lime requires more sand (1 : 3.5), lean sand less (1 : 2).
Gravel, coarse and fine sand and marble flour are used for plaster mortar. In Italy, volcanic tuff.

Tart brick

Filling material known as early as the Middle Ages. It binds brilliantly with lime and forms to some extent a hydraulic mortar (similar to volcanic tuff).

Marble flour

The best from white Canary Island marble. It is used for the last layer of plaster. It binds perfectly with lime.
Mortar for fresco work should be made at least a week before use, stirring daily with a shovel.
By introducing oxygen from the air, we cause calcium carbonate to form in the plaster itself, which reduces efflorescence on its surface.
Plaster prepared for fresco and tempera consists of at least three layers. The lower layers contain a smaller amount of lime, are more lean, the filling material - coarse-grained.
Monumental painting techniques can be divided into two categories:

• Clogging the pores of the plaster - oil technique, oil and wax, resin painting and oily tempera.
• Allowing the plaster to "breathe" - skinny tempera, fresco, glue paint, stereochrome.