Improves Adhesion: The main purpose is to create a strong, durable bond between the substrate and the waterproofing membrane. It seals the pores of porous surfaces like concrete, preventing a direct "pull" on the membrane and ensuring it adheres correctly.
Seals Pores: It fills in minor voids and seals the surface, creating a smooth and uniform base. This is crucial for the success of torch-applied membranes, as it prevents air pockets and ensures a seamless waterproof layer.
Protects the Substrate: It provides an initial layer of protection against moisture, especially on surfaces like concrete foundations and metal that are prone to corrosion.