Membrane mastic is a water-based modified asphalt mastic. It used to fill voids, tie holes, seam edges, overlaps and penetration details prior to waterproofing or dampproofing.
It is a component of foundation waterproofing membranes, systems and dampproofing.
Heavy bodied trowel grade material is waterproof. Use it on the exterior face of foundations to seal water out of the basement.