Posted by Frank Moebus on Mar 15, 2021
While the principle of bond breaking is not new and applies to waterproofing and other industries such as joint sealing, there is still disagreement on what a bond breaker is, what it does and how it applies to the application of a waterproofing membrane. The debate continues, especially over the correct bond breaker for Class III liquid applied membranes. Should you use a polyurethane sealant? Neutral cure silicone? No more Gaps? Or one of those new hybrid sealants?
The short answer to the above is:
“Follow the manufacturer’s instructions.”
If the membrane manufacturer recommends the use of neutral cure silicone, then that’s what you should use. Similarly, if the manufacturer recommends the use of polyurethane sealants or hybrid sealants, then you should use those. I am yet to see a manufacturer recommend the use of “No more Gaps”, so those type of products should probably be off the table.
There are also Class III liquid applied systems, where the manufacturer does not recommend a sealant bond breaker at all. These manufacturers generally recommend the use of a transitioning bandage or bond breaker tape, which usually incorporates a rubber component in the bandage to accommodate the expected movement. Membrane manufacturers generally also recommend these transitioning tapes for Class II and Class I membranes. It goes without saying, that these recommendations should also be followed.
AS3740 - Interpretation of Internal Wet Area Waterproofing
“But AS 3740 states that the membrane can’t bond to the bond breaker, therefore you can only use neutral cure silicone!!!”
Well, that’s actually not the case, so let’s have a look at what the Standard says and doesn’t say. Firstly, AS 3740 does not mention neutral cure silicone anywhere, nor does it mention any other types of sealants or bond breakers.
The definition of a bond breaker according to AS 3740 is:
“A system that prevents the membrane bonding to the substrate, bedding or lining.”
This is often misinterpreted to mean that the membrane must not bond to the bond breaker. By “Substrate” the Standard refers to structural floor and/or wall lining to which a membrane is applied. The bond breaker itself, does not become a substrate. This is illustrated in Fig. 3.7 TYPICAL BOND BREAKER DETAILS. The bond breaker simply forms a separating layer between the substrate and the membrane. There is no reason why the membrane can’t stick to the bond breaker, provided the bond breaker material is capable of accommodating movement.
In the case of Class III membranes, Figure 3.7(c) in the Standard doesn’t require a bond breaker at all. This figure shows that a flexible sealant or fillet is required. Note that the substrates are the areas outside the fillet.
The Standard goes on to say in Note 3 to Table 3.2 that:
“Bond breakers for Class III membranes (high extensibility) allow the membrane to have even thickness.”
Bond Breakers in Waterproofing Systems
It does not say that the membrane must release from the bond breaker and if it is done with the correct sealant as recommended by the membrane manufacturer, the movement will be accommodated as shown in the following illustration.
The membrane and the bond breaker/fillet move together, which has the added benefit that membrane is always supported and therefore more difficult to puncture.
As a matter of interest, the Standard also does not require the membrane to release from the bond breaker for a Class II membrane, provided the tape has elastic properties similar to the membrane:
“Bond breakers for Class II membranes (medium extensibility) allow the membrane to stretch. If a tape is used as a bond breaker, either the membrane will not bond to the tape or the tape will have elastic properties similar to the membrane”.
So, with Class II membranes, there is also no requirement for the membrane to release from the bond breaker.
One other aspect that is rarely considered is that when using moisture cured polyurethane membranes, adhesion between the bond breaker and the membrane virtually guaranteed. Neutral cure silicone or hybrid sealants cannot be used, because the chemistries are not compatible and polyurethane sealants need to be used. The membrane will bond to these sealants. So, if adhesion to the bond breaker is OK for polyurethane membranes, why wouldn’t it be ok for water-based membranes?
It is also important to understand that, when it comes to external waterproofing, there is no difference in bond breaker requirements for different membrane classes in AS 4654.2. This Standard requires a 15mm bond breaker/fillet for all classes of liquid applied membranes. AS 4654.2 does not require the use of tapes for Class I or Class II membranes.
This article tries to dispel some of the myths around bond breakers, especially when used with Class III liquid applied membranes. Whatever bond breaker material might be chosen by the applicator, the most important consideration remains that:
The membrane manufacturer’s recommendations must be followed.