The use of a PE vapour barrier on a cementitious substrate is generally not recommended. Cement-based surfaces are porous and often still contain construction moisture at the start of roofing works. In many cases, a PE vapour barrier does not provide sufficient protection against exposure to high moisture levels within the roof build-up.
Only bituminous vapour barriers offer adequate resistance to construction moisture and ensure the long-term durability of the roofing system in such conditions.
