How much bathroom waterproofing costs in Melbourne
As a standalone job, waterproofing a main bathroom runs $1,400–$2,600 and an ensuite $900–$1,700. The variables are wet-zone area, whether walls are being waterproofed to 1800mm or only to 150mm, hob and threshold detailing, and substrate preparation — a timber floor needing compressed fibre-cement sheeting adds $450–$900 before the membrane is opened. Inside a full renovation, waterproofing is about 5% of contract value. If a quote prices it under $900 on a main bathroom, ask which membrane, how many coats, and who signs the certificate.
Which membrane we use for a bathroom, and why
We install a two-coat certified liquid-applied polyurethane or acrylic-modified membrane, selected against the substrate rather than by habit: polyurethane over concrete slabs and where movement is expected, acrylic-modified over compressed sheeting in dry internal rooms. Sheet membranes are used where a floor waste sits hard against a wall and a liquid system cannot achieve reliable film thickness. Every system we use is certified to AS 4858 and installed strictly to the manufacturer's datasheet — the coat count and cure time in that datasheet is legally binding under AS 3740-2021.
Waterproofing walls: how high, and where
Shower walls are waterproofed to 1800mm above the finished floor. All other bathroom walls get 150mm above floor level, taken to 150mm above a bath lip where the bath abuts a wall, and behind and under any wall-hung vanity. Hobless and level-entry showers extend a minimum of 1500mm horizontally from the shower outlet. Bond-breaker goes into every internal corner and movement joint before the first coat — skipping it is the single most common reason a membrane splits at the floor-to-wall junction within five years.
Waterproofing an existing bathroom without a full rebuild
A compliant membrane sits behind the tile bed, so re-waterproofing means removing tiles from the affected wet zone. Where the failure is contained to the shower, we strip the shower only — floor, hob and walls to 1800mm — reprime, re-membrane, re-screed to falls and retile to match. That is a $4,500–$8,500 job rather than a full renovation. Any product sold as a waterproof coating applied over existing tiles is a temporary surface seal, not an AS 3740 membrane, and will not support an insurance claim.
What you receive at completion
A signed AS 3740-2021 certificate naming the applicator who did the work, the membrane product and batch, dated photographs of the primer coat, first coat and second coat, the recorded cure time observed before tiling, and a six-year workmanship warranty on the membrane and repair area backed by $20M public liability insurance. That package is what insurers ask for years later — and what a subcontracted certificate usually cannot produce.
