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Bond Breakers - Review

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  1. #1
    Join Date
    Oct 2020
    Bowen Mountain

    Default Bond Breakers - Review

    Hello all,
    As per my other thread, I had become increasingly confused between my understanding of how bond breakers work and the feedback from tradies as to how they are applied in practice. Today I decided to ring Gripset for clarification and technical advice since they have many specialised products in this area. I had a good conversation with them from which I realised that some of the concepts that I held were not exactly correct, so I thought I'd share my current understanding here - feel free to correct / comment on anything:

    1. I was under the belief that bond breakers are designed to release from the membrane (does not adhere) in the event of joint movement; however this is not actually true. The bond breaker's job is to provide an extended area that the membrane can still adhere to, where the bond breaker may distort as a whole (eg. the cross-section of a fillet/cove) and distribute the joint movement over a larger area (allowing the membrane a longer distance over which to stretch, rather than the narrow intersection of the joint itself).

    2. I asked why my belief that polyurethane sealants (eg. 11fc) shouldn't be used as bond breakers was contradicted in practice by the people (tilers and specialised waterproofers) that I am seeking quotes from. This is partly answered by 1 above; 11fc can be used as a bond breaker provided that a solvent based membrane is used. However, tile glues (wall tiles) do not work well with solvent based membranes, and if you use water based membranes over solvent based fillers / bond breakers such as 11fc, the outgassing from the solvents causes the membrane to wrinkle/decouple. So therefore not recommended.

    3. If the membrane does decouple, it needs to be reinforced (tape/cloth) or it may fail as it shouldn't be left "loose".

    4. MS (Modified Silicon) sealants are good bond breakers because they are solvent free and do not outgas, and because water based membranes WILL adhere to them.

    5. I suppose that you could still use polyurethane sealants as bond breakers if you could wait a week or two for the outgassing to cease? Note that James Hardie Joint Sealant (recommended by Hardie to seal their scyon joints) is solvent based, but typically this has completed outgassing by the time the waterproofing is done and also it would be painted with primer prior to waterproofing.

    6. The tilers and specialised waterproofers I spoke to seem to prefer solvent based membranes for the floor and water based for the walls; this may be because the solvent based membranes used to be superior, but water based membranes are now class 3 so this shouldn't be the case now ... or perhaps just because the floor is more critical and the need for compatibility (solvent based membrane and solvent bond breaker if using 11fc, etc).

    7. Some of the information on the web may not be accurate as the AS3740 code is well overdue for an update.

    8. So in summary the general recommendations are:
    - Use the same (water based) membrane for walls and floors.
    - Use compatible bond breakers (MS sealants or the specialised rubber joint bands by Gripset, etc)
    - Probably best to stick with a set of products designed from the outset to be compatible from one manufacturer.

  2. #2
    Senior Member
    Join Date
    Jul 2015
    Mornington Peninsula, VIC


    According to the Masters Builders Australia Waterproofing Technical Committee the bond breaker performs 4 functions;

    1. Prevent adhesion of the membrane to the internal corner
    2. Provide a waterproof joint
    3. Accommodate movement at joints
    4. Maintain film thickness across joints

    Point 4 is the least often talked about but one of the most critical. Without a fillet, the membrane pools and you get an undesirable thickness of membrane.

    As for which product. Many waterproofers use PU for one reason only.....it's cheap. You can buy a 600ml sausage of PU for $7-8, a 300ml silicone cartridge is rarely less than $6.

    Silicone is perfect for most applications. PU suitable for some applications. Using manufacturers specialised tapes is ok but they can add undesirable thickness, for instance, an external corner can end up with three overlaps giving 3mm of extra thickness unless you use a pre-made corner (expensive).

    I've never heard of a waterproofer using a solvent membrane on the floor and water based on the wall. How would you join two incompatible membranes? Solvent based membranes for internal wet areas are unheard of these days.

    Here is a chart of what bond breakers you should use with each type of membrane.


  3. #3
    Join Date
    Oct 2020
    Bowen Mountain


    That's interesting info. I'm not sure then if it was a fluke that two of my three quotes stated that they use oil (solvent) based membranes on the floor and water based on the walls then? (I believe that one of them said they used Aldridge membranes who do sell both I believe) I did also wonder about joining the two - I just assumed that overlapping the water based over the oil based (on the walls) would probably give acceptable results.

    Looking at the table, it does support what they told me w.r.t. oil based membranes being superior for the floor (on the basis that PU appears to be the only fillet of choice for them). For the walls they told me that that Water Based membranes are superior for gluing the wall tiles to, and that was why they used both. It would seem to me that it would be simpler for them to just use neutral silicones as you say. Another waterproofer I called also stated over the phone that he used Sika 11FC for all corners. I did try discussing some of these concepts with them, but was told by one that I read too much

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