Waste outlet (wet area)
A waste outlet is the wet-area drain point the membrane is dressed into and the floor falls toward, sealed under AS 3740 and connected under AS 3500.
Ask Chalkline about this →A waste outlet is the wet-area drain point that the waterproofing membrane is dressed into and the floor falls toward. It is the construction junction where the floor waste fixture, the membrane, the screed, and the tile bed all meet, and it is the single most-failure-prone detail in any wet area.
How it differs from a floor waste
The two terms get used interchangeably on site, but they describe different things:
| Term | What it is |
|---|---|
| Floor waste | The plumbing fixture (grate + drain body) installed by the plumber |
| Waste outlet | The constructed junction where the membrane is sealed to that fixture |
A floor waste is a product you buy and install. A waste outlet is a detail you build correctly or fail.
What AS 3740 requires
Under AS 3740:2021, the waste outlet must be sealed so water cannot pass between the membrane and the drain body. The standard route uses a puddle flange (a flat horizontal collar around the drain body) onto which the membrane is bonded, with a reinforcing strip or bandage capping the junction. The membrane must be returned down into the drain body, not just stopped at the rim.
Key requirements:
- Membrane continuous to the outlet: no gap between floor membrane and outlet seal
- Reinforcing strip: bandage or reinforcing fabric over the puddle flange / membrane junction
- Substrate dry and clean before bonding the membrane to the flange
- Falls met: the surrounding floor must fall to the outlet at minimum 1:80 in showers, 1:100 elsewhere
- No reverse fall anywhere within the catchment
Connection under AS 3500
The drain body below the outlet is plumber scope, connected under AS/NZS 3500.3. Minimum drain sizes: 65 mm (showers, bathrooms) or 80 mm (laundries with washing-machine discharge). The plumber sets the outlet rim height; the tiler builds the screed and falls to suit; the waterproofer dresses the membrane in. Three trades, one detail, and the sequencing is fixed.
Sequence
- Plumber roughs in the drain body and sets the outlet rim at the correct height
- Concretor / tiler screeds the floor with falls to the outlet
- Waterproofer primes, applies membrane, dresses it into the puddle flange, applies reinforcing strip
- Waterproofer flood-tests the completed membrane
- Tiler lays tiles over the cured membrane, maintaining falls
A late-add penetration, a wrong rim height, or a missed reinforcing strip at any stage breaks the chain.
Common defects
- Membrane stopped at the flange edge instead of dressed down into the drain body. Water passes under the membrane.
- No reinforcing strip at the membrane-to-flange junction. The most common shower leak.
- Outlet rim set too high for the screed depth. Water ponds rather than draining.
- Outlet rim set too low: tile installs flush to grate but membrane below is exposed in the drain throat.
- Reverse fall around the outlet from sloppy screed work. Water pools instead of draining.
- Puddle flange not flat to substrate: gaps under the flange that the membrane bridges but doesn’t seal.
Most of these are only discovered when water appears on the ceiling below.
For a builder
- The detail is not the fixture. Get the plumber’s outlet selected, set, and sealed before the waterproofer arrives.
- Specify puddle-flange compatibility: not every floor waste comes with a flange suited to membrane bonding. Confirm at order.
- Flood-test every outlet: 24-hour ponded test before tiling is the only way to know the seal works.
- Photograph the detail before tiling. Rectification later requires evidence of how it was built.
Related
See also
Last updated: 2026-05-26. Verified: 2026-05-26. Quarterly review for currency.