An unusual limestone stela from the Egyptian Museum at Cairo was the case study of this research, the stela shows the lady Ta-waher adoring Harmakhis on right and Atum on left; the stela is 37cm in height and 27cm in width. Pharaonic mural paintings (support, mortar, plaster, pigments and paint media) are susceptible to many degradation agents especially in situ. The moisture and heat are the major factors affecting the durability of these substrates. Bio-deterioration is strongly linked to moisture and heat, fungi and bacteria might discolour the painting layer through their own pigments, they can also use the organic compounds from the paint layer as growth substrates.