Understanding Sub-Tile Moisture Migration
Sub-tile moisture migration is a phrase used in the industry, but often not really understood until the issue becomes obvious.
As we all know, there is always the potential for moisture to migrate from the tile surface to the membrane layer. This is why a waterproof membrane is applied prior to the installation of tiles in a tiled shower. The membrane layer protects building elements that can be affected by moisture and, through the design of falls in the shower floor, water is directed to the waste flange beneath the tile surface.
Waterproofing Requirements for Internal Wet Areas
The application of a membrane must follow the IWAM Code of Practice and the requirements of AS3740-2021. So what are the requirements for membrane application?
The IWAM Code of Practice requires that all internal wet areas have a membrane layer applied to protect building elements that are likely to be damaged when exposed to moisture. AS3740-2021 specifies the same requirement.
If the membrane is applied to protect building surfaces, how is moisture contained within a wet area?
The Importance of Waterstops
Both the IWAM Code of Practice and AS3740 state that membrane installation must include the installation of a waterstop.
What Is a Waterstop?
AS3740-2021 defines a waterstop in Section 1.3.42 as:
“A vertical extension of the waterproofing system forming a barrier to prevent the passage of moisture in the floor or vertically in a wall.”
Waterstops Are a Mandatory Part of the Waterproofing System
AS3740-2021 further states:
AS3740-2021 Clause 4.8 – Waterstops
4.8.1 General
“Waterstops shall be installed to retain water within the shower area or wet area. Waterstops are an integral part of the waterproofing system and shall conform with Clauses 4.8 and 4.9.”
The standard clearly states that waterstops are an integral part of the waterproofing system.
The Cambridge Dictionary defines integral as:
“An essential or indispensable component required to make a whole complete.”
The use of the word shall within AS3740-2021 indicates a mandatory requirement.
Where Should Waterstops Be Installed?
AS3740-2021 and the IWAM Code of Practice require waterstops to be installed at critical transition points where moisture migration could occur.
Typical Waterstop Locations
Waterstops should be installed:
- At the transition point separating the shower area from the bathroom floor.
- On walls adjacent to doorways where moisture containment is required.
- Behind shower glazing channels where direct water exposure is expected (recommended by TANZ).
- At the doorway of a wet area to prevent moisture migration into adjacent spaces.
Correct installation of waterstops is essential to ensure the waterproofing system performs as intended and complies with both AS3740-2021 and the IWAM Code of Practice.
Want to learn more? – Contact TANZ