Fully-Bonded Pre-Applied Waterproofing Membrane

Self-adhering sheet waterproofing can be either pre- or post-applied, meaning it is installed either before or after concrete placement. For an example of post-applied self-adhering sheet waterproofing, see the Foundation Waterproofing Sheet Membrane CP. Pre-applied waterproofing can be either bonded or not. Bonded pre-applied waterproofing can utilize either a mechanical bond (via nonwoven fabrics where the concrete interlocks with the fibers) or a chemical/adhesive bond (where the concrete establishes a chemical bond with the adhesive), or both. Some also utilize swellable sealing layers like bentonite - see the Bentonite Sheet Waterproofing CP for an example. The advantage of chemical bonds over mechanical bonds is that they stop horizontal water migration between the membranes and the surface of the concrete. Chemical/adhesive bonded membranes are further distinguished as either modified bitumen or other synthetic adhesives. This CP is focused on fully bonded, pre-applied waterproofing membranes that are composed of a polymeric film and a non-bitumen synthetic adhesive that chemical bonds to concrete. These products can be used in both horizontal and vertical applications. For vertical applications, the membrane is attached to the concrete form or lagging with the adhesive portion facing toward the cavity in which the concrete will be poured. For horizontal applications, the product is applied to compacted soil or gravel or to a concrete slab, with the adhesive portion facing upward, and concrete is cast against the membrane. In order to prevent sticking while on the roll, and so that the membranes can be walked on, there is typically a topcoat applied to the adhesive. The topcoat is at least partially soluble at the high pH levels found in concrete, allowing bonding with the adhesive layer. Alternatively, a release liner may be applied across the adhesive surface and must then be removed prior to installation of the concrete.