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.