The Importance of Bond Breakers

What is a bond breaker and why would you use one? A bond breaker, as stated in Australian Standard 3740 is a “system that prevents the membrane bonding to the substrate, bedding or lining”. A bond breaker, literally breaks the bond between the substrate and waterproofing membrane to create an elastic ‘bridge’ that can stretch as buildings flex and move. The bond breaker is applied in joints where walls meet floors or two walls meet in a corner. They are also used over movement joints. These are points that are most likely to experience flex and movement and the hardest to get a proper seal with the membrane without a bond breaker. Normally a bond breaker would be either a silicone applied by caulking gun, tape – either applied by placement under the waterproofing membrane, or a self adhesive tape. If gaps are large then backing rods are available in a range of sizes. Once the bond breaker has been applied and allowed to cure, the waterproofing membrane can be added over top.

Using a bond breaker is one of the most crucial components of waterproofing and is often overlooked, undermining the whole purpose of a waterproofing membrane. If bond breakers aren’t used as part of a waterproofing system, there is a high chance the membrane will tear, creating holes which would allow moisture onto the substrate below, rendering the membrane pointless.

It is important that the correct bond breaker is applied in each situation. For example, the compatibility between bond breaker and the covering membrane needs to be considered depending on the elongation properties of the selected waterproofing membrane. If a membrane is Class I it requires a 75mm bond breaker, Class II membranes require 35mm and lastly a Class III membrane will require a 12mm bond breaker. Keeping this in mind will help understand if a silicone or backing rod is more applicable for the required joint. 

The other consideration is whether a neutral cure silicone is more suitable than a PU. Many installers like to us a PU but these take longer to dry and must be fully cured to ensure there is no gassing off that happens below any water-based membrane. Both PU and Silicone must be suitably cured to ensure the membrane does not stick which negates the use of the bond breaker in the first place.

Bostik bond breaker systems

Depending on the waterproofing membrane that will be applied from the Dampfix range, Bostik has neutral cure silicones such as Bostik V70 or Bostik 6S, Bostik Bandage which is a tape applied under the first layer of wet membrane or Bostik Seal N Flex Advance which is a polyurethane available in sausage or cartridge formats for easy application.

While they might seem like a small and insignificant part of the job, bond breakers are important to the overall integrity of a waterproofing job. 

Refer to the Technical Data Sheet of your chosen membrane for the appropriate bond breaker to be used.

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