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About Waterproofing

Helpful information about Waterproofing…

Waterproofing of structures above or below the ground, where high ground levels are in-contact with the building or structure, is primarily carried out in four ways. Here we outline Rendering, Cavity Drain Membrane systems and cementitious coatings.

Multi-Coat Renders…

This design of waterproofing uses renders and screeds modified with chemical additives and are applied by conventional rendering and screeding techniques in multiple layers. The number of layers required is dependent on the conditions likely to be experienced and are normally specified by the material manufacturer.

Cementitious Coatings…

This design of waterproofing uses pre-mixed compounds comprising of cement, graded aggregates and chemical additives. They are supplied in powdered form and mixed with water and are applied by brush, trowel or spray techniques to form a coating of between 1mm and 3mm thick.

Liquid Applied Membranes…

This design of waterproofing uses various materials such as bitumen notably RIW Liquid Asphaltic Composition, elastomeric urethanes and epoxy.

Most liquid applied membranes require a loading coat to keep them in place although epoxy systems can be applied directly onto the substrate provided it is sound.

These cavity drain membrane systems tend to be vapour barriers and thus commonly used over floors as they perform as both a vapour check and as a wearing coat.

Cavity Drained Membranes…

This design of waterproofing uses high density polyethylene sheet materials over the walls, floors and arched or sloping ceilings but not flat ceilings because of the risk of water ponding/pooling. Extruded moulded studs on the reverse of the sheet material serve to hold the product away from the substrate allowing an air gap behind the system in which water and water vapour can move unhindered in all directions thus achieving ‘damp pressure equalisation’. Water entering the structure behind the membrane is collected within a drainage conduit at the base of the wall and taken to a sump chamber where a sump pump will dispose of it in a controlled way.

The weakest point of any below ground structure is deemed to be the floor/wall joint (the juncture where the floor abuts the wall) and thus the most susceptible to water ingress. Here-to water pressure is equalised and controlled by the installation of the drainage conduit.


All of the above designs, systems and materials have a place in the modern world to ensure a dry habitable environment however consideration of failure for numerous reasons must always form part of a competent surveyors waterproofing design.

The problem with all systems, except Cavity Drained Membranes systems, is the substrate over which they are applied must be suitable for adhesion and bonding. This is rarely the case, resulting in the need for expensive preparatory works. Furthermore, the significant risk of puncturing by something as simple as hanging a picture is a major factor of consideration. The risk of atmospheric condensation, which is a health hazard, is exacerbated because of cold dense surfaces.

Within B.S.8102 it is documented that Cavity Drained Membrane systems are the least likely to fail. The membrane is not designed to do any more than provide a dry liner skin to separate the wet substrate and dry interior.