Lewis & Short

albārĭus, a, um, adj. [albo], only in archit., pertaining to the whitening of walls.
Hence, albārĭum ŏpus, or absol. al-bārĭum, white stucco, a mortar composed of lime, gypsum, and a little fine river sand, with which walls were covered and made white, Vitr. 5, 2, 10; 7, 2, 3; Plin. 35, 16, 56, § 194; 36, 24, 59, § 183; also, with the form albāris, e: OPVS ALBARE, Inscr. Orell. 4239.albārĭus tector, a worker in stucco, a plasterer, Tert. Idol. 8; or absol. albārĭus, Cod. Th. 13, 4, 2, and Inscr. Orell. 4142.