When we formed BBR Roofing in the early 1990’s options for waterproofing complex details on bitumen felt roofs were fairly limited.
Some of the high performance felts of the time were very thick and heavy such as the HT350 and subsequently popular 350 elastomerics. These membranes were not only thick, but their elastic memory made them difficult to apply to three dimensional details. Thinner ‘Detailing’ membranes were provided by the manufacturers, which allowed for more effective simple detailing such as upstands and drips, but still difficult to apply effectively to more complex details.
For pipe penetrations a variety of collars formed from various metals and/or rubbers & plastics are available, but these are really only successful where pipes are clearly separated from other features. Pipes adjacent to walls or in combination with other pipes present more of a waterproofing challenge.
Traditional methods of waterproofing these complex details have often relied on forming some sort of timber boxing around the detail, which can then be waterproofed with the bitumen material. This often leaves a weak point where the bitumen membrane terminates.
Other roof furniture and penetrations often present difficult waterproofing situations, such as HAV plant and structural beams and columns.
The development of liquid applied waterproofing over the past 20 or more years has now allowed an additional resource for waterproofing complex details on bituminous membrane roofs. Previously roofing systems manufacturers took a single-minded approach to their products – roofs had to be completely bituminous or completely liquid applied. In addition, bitumen felt manufacturers would limit their guarantee to only their own materials. Today, most roofing membrane system suppliers offer a liquid applied waterproofing product to be used in combination with their membranes, as part of a whole-system approach.
Liquids have the advantage that they can bond to substrate materials such as metals, plastics and masonry/concrete to form a waterproof seal, whereas bituminous membranes rely on adhering to the substrate but need some form of mechanical termination to prevent capillary water ingress behind the membrane.
When given the aesthetic finish of a mineral matching the membrane, applied while the liquid is still wet, a subtle blend of membrane and liquid is achieved.
The process is as follows;
o The bitumen membrane is dressed as far as practical up to and around the detail.
o The substrate material is then cleaned. Metals should be abraded back to clean metal.
o For an aesthetic finish extent of the liquid waterproofing area can be finished with masking tape.
o Appropriate primers should be applied to the substrate material, as provided by the system supplier.
o The liquid system is applied such as to overlap sufficiently onto both the detail substrate and onto the bitumen membrane. There are different types of liquid products available, but in principal they will usually be applied in two or three coats, with a reinforcement fabric such as glass-fibre or polyester fleece inlaid to cover the termination of the membrane.
o While the liquid waterproofing is still wet a layer of loose mineral, as supplied by the membrane manufacturer, is ‘thrown’ at the liquid surface to create a finish consistent with the rest of the roof covering.
The adoption of combination membrane-liquid detailing by bituminous system suppliers has led to far more flexibility in treating complex detailing, providing more efficient longer term waterproofing security for bituminous flat roof coverings.