AS 3740:2021 Waterproofing of Domestic Wet Areas 4.4.1: 4.4.1 Surface preparation and substrate falls

Before membrane application the substrate must be smooth, with no protrusions, voids or formwork distortion, and it must be clean and dry with no dust or contaminants. It must be treated to prevent pin-holing from substrate degassing during curing and to secure adhesion. Substrate falls must follow 2.3.1 (Clause 4.4.2). Notes suggest a surface at least as smooth as a wood-floated or lightly broomed finish, a primer where the membrane requires it, and mechanical correction of irregularities.