Intonaco is an Italian term for the final, very thin layer of plaster

Plaster

Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...

 on which a fresco

Fresco

Fresco is any of several related mural painting types, executed on plaster on walls or ceilings. The word fresco comes from the Greek word affresca which derives from the Latin word for "fresh". Frescoes first developed in the ancient world and continued to be popular through the Renaissance...

 is painted. The plaster is painted while still wet, in order to allow the pigment to penetrate into the intonaco itself. An earlier layer, called arriccio, is laid slightly coarsely to provide a key for the intonaco, and must be allowed to dry, usually for some days, before the final very thin layer is applied and painted on. In Italian the term intonaco is also used much more generally for normal plaster or mortar wall-coatings in buildings.

Intonaco is traditionally a mixture of sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

 (with granular dimensions less than two millimeters) and a binding substance.

Types of intonaco

Different types of intonaco are classified based on the binding material used:

• Intonaco based on lime
  Lime (mineral)
  Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...
  
  , where the only binding substance is hydrated lime
• Intonaco lime/cement, where the binding element is a mixture of hydrated lime with Portland cement
  Portland cement
  Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
  
  , with a majority of lime
• Intonaco cement/lime, where the binding element is a mixture of hydrated lime, and Portland cement, with a majority of Portland cement
• Intonaco with a plaster base, where the binding element is exclusively plaster

The sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

 utilized in the intonaco can be limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 or silicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

, taken from a natural source such as a river or from sand that is pulverized.

Types of stabilizers

Intonaco can be stabilized using:

• Lime
• plaster
• Calcium-sulfate based plaster
• Terracotta-based cement