Prior to applying dampproofing, how thick must the portland cement parging be applied to the exterior of masonry walls?

The correct thickness for portland cement parging applied to the exterior of masonry walls prior to dampproofing is 3/8 inch. This specific thickness is crucial because it ensures that the parging layer adequately protects the masonry structure from moisture infiltration while also providing a surface to which the dampproofing can properly adhere.

Parging that is too thin may not offer sufficient protection or adequate bonding surface, potentially leading to moisture issues in the future. Conversely, if the parging is applied too thick, it may not cure properly or may develop cracks, compromising its integrity and effectiveness in moisture management. The 3/8 inch thickness strikes a balance, providing sufficient mass to resist moisture movement while minimizing risks associated with application and curing.