The second most common recurring problem, after poor surface preparation, is the failure to prime the respective parts and surfaces before the application of the waterproofing membrane. Failure of the waterproofing membrane bond to substrates is a recurring and consistent problem often associated with poor subsurface drainage and saturation of tiling or topping screeds.

Every manufacturer of a sealant or a waterproofing membrane specifies priming of surfaces. There are primers available for a large range of materials to enhance adhesive bond strength of both sealants and membranes. Most membranes currently on the market will not form a chemical waterproof bond to Polyvinyl Chloride (PVC) products.

In the case of flashing angles and waterstop angles, PVC should not be used and aluminium angles used wherever possible. Where PVC is located at drainage wastes and drainage flanges the PVC must be primed to adhere the sealant or waterproofing membrane.

Surface priming for CFC, concrete, mortar screeds and plywood substrates should always be carried out with the manufacturers specified primers. Surface priming will reduce porosity, dusting, air entrapment (pin holing) and high residual moisture in the substrate which will cause blistering of the membrane after curing.


Not all primers are the same. Some primers, single part solvent or water based, are used primarily to seal the surface and improve adhesion of the membrane. Two part water based epoxies work in the same manner but can also seal off high residual moisture in the substrate.

Membrane application must be completed within a limited time frame before the epoxy is cured beyond 24 hours. Epoxy primers for residual moisture are described as Moisture Suppressant Coatings (MSC) and the product must have a certified test result according to American Society for Testing and Materials (ASTM) E96 Standard test methods for Water Vapour Transmission of Materials.

NEXT TIME: Substrate Moisture