Waterproof vs Water-Resistant: The AS 3740:2021 Materials Lists and the Compatibility Chain
AS 3740:2021 sorts every material in a wet area into one of two groups: waterproof, or water-resistant. The list is short and it is in Clause 3.3. Most failures happen not because a material is on the wrong list but because two compliant materials were never checked against each other. This article reproduces the lists as a working reference and walks the compatibility chain in Appendix E.
1. The distinction, and why it decides the build-up
A waterproof material is deemed to stop water on its own. A water-resistant material does not degrade when wet, but it does not stop water; wherever the NCC requires an element to be waterproof, a water-resistant material needs a waterproof layer somewhere in the assembly. Tiles, plasterboard and fibre cement are all water-resistant. None of them is a waterproofing system.
Which elements must be waterproof and which merely water-resistant is decided by the NCC, not the standard: Housing Provisions Clauses 10.2.2 to 10.2.5 for a Class 1 house (shower walls waterproof to 1 800 mm, shower floors waterproof, timber floors outside the shower waterproof, concrete floors outside the shower water-resistant, and so on), and Specification 26 of Volume One for Class 2 to 9 buildings. AS 3740 then tells you which materials satisfy each label.
2. Materials deemed waterproof (Clause 3.3.1)
| Material | Condition in the standard | Typical use |
|---|---|---|
| Stainless steel | None stated | Preformed trays, linear drain channels |
| Copper | Not less than 99.9% copper, designation 110 or 122 to AS 1566 | Sheet trays and flashings |
| Flexible waterproof sheet flooring | Sealed and welded joints, meeting AS/NZS 4858 | Continuous vinyl floors; no waterstop needed at the room doorway (Note 1 to 3.3.1) |
| Wet-area membranes | Meeting AS/NZS 4858 | Liquid-applied and sheet membranes, the usual system |
| Glass | Meeting AS 1288 | Shower screens and panels |
| PVC | Meeting AS 3500.2 | Drainage components |
Two traps in that list. Glass and PVC are "waterproof" as materials, which is why a screen or a waste is not itself a weak point; the junctions around them are, and those are governed by Clauses 4.8 to 4.12. And Clause 4.16 is explicit that welded resilient flooring which does not meet AS/NZS 4858 is water-resistant, not waterproof, so a vinyl floor is only a waterproof floor if the product and the welding both meet the standard.
3. Water-resistant substrates (Clause 3.3.2)
| Location | Substrate | Standard |
|---|---|---|
| Walls | Concrete | AS 3600 |
| Walls | Cement render | No product standard; preparation to Clause 4.4.5 |
| Walls | Fibre cement sheeting | AS/NZS 2908.2 |
| Walls | Water-resistant plasterboard | AS/NZS 2588 |
| Walls | Masonry | AS 3700 |
| Walls and floors | Structural plywood | AS/NZS 2269 series, installed to AS 1684.2, .3 or .4 |
| Floors | Concrete | AS 3600 and AS 2870 |
| Floors | Compressed fibre cement sheeting | AS/NZS 2908.2 |
| Floors | Fibre cement sheeting on a structural floor | AS 2908.2 |
The closing sentence of Clause 3.3.2 is the one that matters: the substrate material must not degrade when exposed to moisture. Standard plasterboard fails that test, which is why it is not on the list.
Figure 4.6.2 — Membrane termination at shower with hob
4. Water-resistant surface materials (Clause 3.3.3)
| Location | Surface material | Condition |
|---|---|---|
| Walls | Thermosetting laminated sheet | AS/NZS 2924.1 |
| Walls | Pre-decorated fibre cement | AS/NZS 2908.2 |
| Walls | Ceramic and stone tiles | On a Clause 3.3.2 substrate |
| Walls | Flexible sheet wall material with sealed joints (sheet vinyl) | On a Clause 3.3.2 substrate |
| Walls | Sanitary-grade acrylic or polymer linings | None stated |
| Walls | Glass | AS 1288 |
| Floors | Ceramic and stone tiles | On a Clause 3.3.2 substrate; porous tiles can discolour from water migration |
| Floors | Flexible sheet flooring with sealed joints (sheet vinyl) | Installed to AS 1884 (the installation standard for resilient flooring) |
| Floors | Concrete | None stated |
5. Sealants, fastenings and adhesives (Clauses 3.5 to 3.7)
Sealants must be waterproof or water-resistant as the location demands, flexible, mould-resistant and compatible with the materials either side. Junction sealants are typed (Type 1, 2 and 3 in Clause 4.11.1) by where they are used.
Fastenings for sheet linings must be compatible with the sheet and spaced so they do not compromise the membrane; fibre cement needs screws made for it.
Adhesives must be compatible with what they bond. The standard's own example: a tile adhesive must be water-resistant to bond tiles to a waterproof or water-resistant surface.
6. The compatibility chain (Clause 3.2 and Appendix E)
Clause 3.2 is one sentence: components throughout the entire waterproofing system shall be compatible. Appendix E explains what "entire" means and warns of the symptoms of getting it wrong: bubbling, blistering, retarded curing and delamination. Figure E.1 draws the chain. Read it as a checklist of interfaces, each of which needs a manufacturer's statement or a tested system behind it:
Figure E.1 — Compatibility chain
Substrate: must accept the primer and the membrane, and be dry enough (Appendix F for concrete and timber subfloors).
Substrate primer: chemically compatible with the membrane; porous and non-porous substrates may need different primers (E.2.2).
Junctions and connectors: membrane terminations, transitions and junction sealants compatible with each other (E.2.3).
Bond breakers and fillets: matched to the elasticity class of the membrane and chemically compatible with it (E.2.4; Table 4.10).
System components: waterstops, drainage control flanges, fittings and coves, compatible with the junction sealants or isolated by a primer that suits both.
Membrane: compatible with the substrate, the components and the finish above it.
Surface-finish primer or isolation underlay: where the membrane is not itself a suitable substrate for the finish.
Surface-finish adhesive: must not compromise the membrane or the drainage at membrane level; rated for wet areas.
Fillers, grouts and sealants: must not change the membrane's elasticity class or block sub-surface moisture movement.
Penetration sealants: compatible with the membrane and the fixture (Clause 4.12).
The practical rule that falls out of the chain: specify the membrane manufacturer's full system (primer, bond breaker, sealant, and the adhesive they have tested over it), or obtain written compatibility statements for every substitution. "Wet-area rated" on a tub of adhesive is not a compatibility statement.
7. The failures the chain predicts
| Failure | Broken link | Prevention |
|---|---|---|
| Membrane lifting from the substrate | Primer not matched to a non-porous substrate, or substrate too wet | Primer per substrate type; Appendix F moisture test |
| Cracked membrane at wall–floor junctions | Rigid fillet under a Class III membrane | Bond breaker to Table 4.10, matched to elasticity class |
| Tiles debonding months later | Adhesive attacking or not keying to the membrane | Adhesive from the tested system, or a written compatibility statement |
| Blistering under the membrane | Solvent-based product over a water-based one, or vice versa | Single-manufacturer system; check the data sheets for solvent compatibility |
| Leak at a waste or tap | Flange or penetration sealant not compatible with the membrane | Flanges and sealants from the system; Clauses 4.3 and 4.12 |
On timing: these defects usually surface within the first year or two. That is inside the statutory warranty period in every state (NSW: two years for general defects and six for major defects under the Home Building Act 1989; Queensland: 12 months non-structural and six years six months structural under the QBCC scheme; Victoria: the implied warranties in the Domestic Building Contracts Act 1995, with a 10-year limitation from the occupancy permit). A compatibility failure is a builder's problem before it is the owner's.
8. Worked selections
Standard bathroom, timber-framed house
Walls: water-resistant plasterboard (AS/NZS 2588) or fibre cement (AS/NZS 2908.2); floor: compressed fibre cement on joists, or structural plywood to AS/NZS 2269 installed to AS 1684. Timber floors outside the shower must be waterproof under Housing Provisions 10.2.3.
Membrane: liquid-applied to AS/NZS 4858, with the manufacturer's primer, bond breaker and flanges. Membrane up shower walls to 1 800 mm (Clause 4.6.3).
Finish: ceramic tiles on the tested adhesive; flexible sealant at all junctions.
Sheet vinyl laundry or accessible bathroom
Substrate: compressed fibre cement or concrete, surface profile prepared to Clause 4.4 (AS 1884 Appendix E for concrete surface profile).
Flooring: welded sheet vinyl meeting AS/NZS 4858, so the floor itself is the waterproof layer and no doorway waterstop is needed; installed to Clause 4.16 (overlap, welded or push-in waste methods, Figures 4.16(A) to (C)).
If the vinyl does not meet AS/NZS 4858, an AS/NZS 4858 membrane goes under it wherever the NCC requires waterproofing.
Figure 4.16(A) — Vinyl installation — Overlap method
Figure 4.16(C) — Vinyl installation — Push-in vinyl sheet waste
Check it against the source
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Sources: AS 3740:2021 Section 3, Clauses 4.10 to 4.16 and Appendices E and F (Standards Australia); ABCB Housing Provisions Part 10.2. Figures reproduced for review and commentary. Part 1 of this series: AS 3740:2021 explained. First published 1 September 2026; rebuilt around the standard's own tables 2 September 2026.