Mortar will generally fail to stick to non-porous, smooth, flexible, or contaminated surfaces such as plastic, glass, sheet metal, painted walls, wood, and heavily waxed or sealed stones. Because standard cement-based mortar relies on mechanical suction and porous absorption to anchor itself as it cures, slick surfaces provide no microscopic grip for the cement crystals. Additionally, mortar will not adhere well to dirty, dusty, oily, or frozen surfaces where debris or ice acts as a physical barrier between the mortar and the substrate, immediately causing the bond to fail under minimal stress or environmental vibration.
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