Granada ++ Alhambra ++ Mocárabe (ornamental desgin) was constructed in a variety of materials including wood and plaster. Under the Nasrid, mocárabe was originally carved into its medium. Later on, moulds were made to cast the designs with clay or plaster.
-from Wikipedia (http://en.wikipedia.org/wiki/Moc%C3%A1rabe)

Apparently these stuff really can stay on for long! From what I heard, the stuff they use to sustain these works are...applying egg white after putting them on the walls. On how they make these stuff, they make the negative of the design as a mould.