What must be waterproofed
Shower floor plus 150mm up all walls, shower walls to 1800mm, entire bathroom floor if the door step is less than 25mm above finished floor level, and the full perimeter to 150mm on walls behind vanities and baths.
The membrane system we install
Primer, then bond-breaker at internal corners, then two liquid coats — perpendicular to each other — of a certified membrane. Total dry film thickness is verified before tiling.
How to check a certificate is real
A legitimate AS3740 certificate names the individual applicator, lists the product used, includes photographic evidence, and is signed on the day of application — not backdated.
Common non-compliance we see
The failures we most often uncover behind a leaking Melbourne shower: single-coat membranes (spec is two), missing bond-breaker at internal corners, membrane skipped behind hob timbers, screed laid without falls to the drain, and 'topical' membranes painted over existing tiles as a supposed fix. All of these void insurance claims.
Substrate preparation before membrane
AS3740 compliance starts before the membrane goes on. Timber substrates need compressed fibre-cement sheeting or equivalent, screwed at 200mm centres. Concrete slabs need primer suited to the moisture content, verified with a hygrometer. Corners need 45mm cove-flashing where walls meet floor. Skip any of these and even the best membrane will delaminate within five years.
Warranty implications
In Victoria, waterproofing carries a statutory six-year warranty. Our own workmanship warranty is six years on the membrane and repair area, backed by our $20M public liability insurance. Insist on both — a builder unable to warrant six years is telling you something about their confidence in the installation.
AS 3740 wall heights, in millimetres
The numbers that get argued about on site, straight from the standard: shower walls waterproofed to 1800mm above the floor waste; shower floor plus 150mm up every enclosing wall; 150mm above the floor on all other bathroom walls; the full floor where the room has a step-down or the door threshold is under 25mm; 150mm above a bath's lip where the bath abuts a wall; and behind and under any vanity where the basin is fixed to the wall. Where a shower has no hob, waterproofing extends a minimum of 1500mm horizontally from the shower rose outlet.
How AS 3740-2021 changed from the 2010 edition
Four practical changes matter to homeowners. Shower-floor coverage is defined more strictly for hobless and level-entry showers. Membrane manufacturers' instructions are now explicitly binding, so a two-coat product cannot legally be applied in one pass. Bond-breakers at movement joints and internal corners are mandatory rather than recommended. And penetrations — floor wastes, tap bodies, shower rails — must be sealed with a compatible flange or collar, not just membrane painted over the hole.
Who is legally allowed to waterproof in Victoria
In Victoria, waterproofing of wet areas in domestic building work is registered work. Where the value of the waterproofing exceeds the statutory threshold, it must be carried out or supervised by a person registered with the VBA in the waterproofing class, and domestic building insurance applies. Our waterproofers are in-house and named on the certificate — which is what an insurer asks for if a claim is ever made, and what a subcontracted paper trail cannot provide.
What to ask before the tiler starts
Three questions, asked in this order, will tell you whether the membrane under your tiles is compliant: (1) which membrane product and how many coats, with the datasheet; (2) photographs of the primer, first coat and second coat, dated; (3) the cure time observed before tiling, which is normally 24–72 hours depending on product and humidity. If the answer to any of the three is vague, do not let the tiling start — once the tiles are down, verification means demolition.
