The present paper addresses the development, application and in situ behaviour monitoring of a number of restoration materials. This are designed for treatment of gaps of the mural painting support of the monuments situated in wet climate as well as exposed to capillary humidity. The materials are required to have low content in SO₃ and soluble salts, and good strength and freeze-thaw resistance. Such materials have been applied on both interior and exterior surfaces in the Sfinţii Arhangheli Mihail, Gavriil şi Rafael Church (19^th century AD) in the Sfântul Grigorie Decapolitul cave of the Bistriţa Monastery, Vâlcea County, Romania. The behaviour of the composite materials was monitored over two years.