Noun
intonaco (plural intonacos or intonacoes or intonaci)
The final, very thin layer of plaster on which a fresco is painted.
Coordinate term: arriccio
Once a giornata is dried, no more buon fresco can be done, and the unpainted intonaco must be removed with a tool before starting again the next day. Source: Internet
If mistakes have been made, it may also be necessary to remove the whole intonaco for that area—or to change them later, a secco. Source: Internet