Such permeable structures allow water vapor to be transmitted, but also allow liquid water to penetrate. Liquid water or moisture can penetrate permeable masonry building materials due to natural capillary absorption.
Water is the main cause of deterioration of masonry building materials.
Problems such as rising damp, moisture penetration, dampness through shower or bathroom walls, efflorescence on external walls, stains, fungi or algae growth, concrete corrosion, and loss of thermal insulation are all due to water penetration. Surface coating or membranes can stop water penetration by forming a continuous film to block the open capillaries of the masonry materials. However, surface coatings or membranes are not an ideal method to protect masonry from penetrating damp. This is because surface coatings may stop water vapor transmission resulting in wet walls due to condensation of water vapor within the capillaries. Water may still penetrate into the masonry through hairline cracks in the coating film.