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Bond Breakers in NSW Houses: Does the 12 mm Rule Apply?

Written by Kevin Ly

A bond breaker is the tape or sealant at a wet-area junction that stops the membrane bonding across the corner. On site, arguments about it usually come down to one number, 12 mm. Some people treat that as the rule for every bathroom. In a house it may not apply at all, depending on which route the plans follow. Either way, where the membrane is bonded at the junction, a bond breaker is still required.

The short answer

These are the Deemed-to-Satisfy routes, the ones that follow the standard details. A performance solution is a separate path and isn't covered here.

Why there is a bond breaker at all

Where a wall meets a floor, or two walls meet, the two surfaces move separately. If the membrane is stuck hard to both sides right into the corner, any movement is concentrated on a very small strip of membrane. The bond breaker gives the membrane room to cope. The Housing Provisions' explanatory notes describe it by membrane type: a low-stretch membrane gets room to flex, a medium-stretch membrane gets room to stretch, and a high-stretch membrane keeps an even thickness through the corner.

That is why both routes tie the bond breaker to the membrane's flexibility class. The class comes from how far the membrane stretches before it breaks, and the product's data sheet should state it.

Two routes for a house

For a Class 1 house, NCC 2022 Volume Two gives two Deemed-to-Satisfy routes for wet areas (H4D2 and H4D3):

On both routes, which parts of the room have to be waterproof or water resistant comes from Housing Provisions 10.2.1 to 10.2.6. NSW has no variation to these clauses.

What each route says about bond breakers

The Housing Provisions (10.2.27) say that bond breakers must be installed at all wall/wall, wall/floor and hob/wall junctions, and at movement joints, where the membrane is bonded to the substrate. They must be a type that suits the flexibility class of the membrane. No minimum width is set.

AS 3740 (cl 4.10) asks for a fillet or a bond breaker at every change of plane or material, and at movement joints, where the membrane is bonded. Its Table 4.10 then sets a minimum bond breaker or tape width for each membrane class. For Class III, the high-stretch membranes, the minimum is 12 mm. The less stretchy classes need wider bond breakers.

So on the Housing Provisions route, the NCC sets no minimum width. It still asks for a bond breaker at those junctions where the membrane is bonded, of a type that suits the membrane's class. Whether a particular junction meets that is your certifier's decision.

Apartments

For Class 2 and 3 buildings, NCC 2022 Volume One (F2D2) requires wet areas to meet Specification 26 and AS 3740. Specification 26 sets which surfaces must be waterproof and doesn't deal with bond breakers. There is no Housing Provisions route, so AS 3740's minimum widths apply.

Before you argue about the 12 mm

  1. Which route do the plans and specification name? AS 3740, or the Housing Provisions? For an apartment, it is AS 3740.
  2. What class is the membrane? Check the data sheet for the product that was actually used, in the version current when it went on.
  3. What does the data sheet show at the junction? Manufacturers sometimes set their own junction detail, and some say which tapes or sealants can be used with their membrane. That is the manufacturer's instruction, separate from the NCC.

When it can be checked

A bond breaker can be checked until the junction is covered. Its width can still be measured after the membrane goes over it. Once the junction is tiled, or covered with screed, it can't be seen or measured at all. The time to check is before tiling or screeding, or with photos taken before then.

What we record

At a pre-tile inspection we record the route the plans and specification name, the membrane and its class as stated on the data sheet, and each junction: whether a bond breaker is there, what type it is, and its width where it can be seen and measured. Photos are taken with the tape or rule in the frame. We record what is there against the route the documents name. Whether the work complies is your certifier's decision.

See what a pre-tile inspection covers, or email us your plans, the membrane's data sheet and where the job is up to.

Send your waterproofing query

What's changing

NSW adopts NCC 2025 on 1 May 2027. The clause numbers on this page are from NCC 2022, which applies in NSW until then. We will update this page when that changes.

This page is general information for NSW as at November 2026, not advice about a particular building.

Sources