Silicone sealants: neutral cure vs acetoxy, wet area vs glazing grade

TL;DR

Silicone sealants are the go-to for wet-area tile joints, glazing perimeter seals, and kitchen splashbacks: they outlast polyurethane by roughly three times under UV exposure and stay flexible from -40°C to +150°C. The critical selection call is neutral cure vs acetoxy. Neutral cure (no acetic acid byproduct) is required on natural stone, copper, brass, and most waterproofing membranes; acetoxy is faster-curing and cheaper but attacks these materials. Neither type is paintable once cured, which is the most common site mistake. For any seal in contact with drinking water (kitchen bench, plumbing fixture), confirm AS/NZS 4020:2018 approval on the product data sheet before applying.

What it is

A silicone sealant is a one-component elastomeric sealant based on polydimethylsiloxane chemistry. It cures by reacting with atmospheric moisture to form a flexible, waterproof rubber bead that accommodates joint movement without cracking.

Two cure systems dominate the residential market:

Acetoxy cure: releases acetic acid (vinegar smell) during cure. Faster skin time (typically 5-13 minutes), cheaper, and well suited to glass-to-glass and glass-to-aluminium glazing joints. Not suitable on natural stone, copper, brass, bituminous waterproofing materials, or most cement-based substrates.
Neutral cure: releases alcohol instead of acid. Slower to skin (10-40 minutes depending on colour), slightly higher cost, suitable on the full range of building substrates including stone, metals, and waterproofing membranes. The standard choice for wet-area tile joints and exterior seals.

Common brand examples verified on manufacturer data sheets:

Selleys Wet Area Silicone: 100% neutral cure, mould resistant, wet areas (Selleys Australia, verified 2026-05-11)
Sika Sikasil-702: neutral cure, AS/NZS 4020:2018 approved, internal and external (Sika Australia, verified 2026-05-11)
SikaSeal Kitchen and Bathroom: neutral cure, AS/NZS 4020:2018 compliant, wet areas (Sika Australia, verified 2026-05-11)
Sika Sikasil GP (acetoxy): general-purpose acetoxy cure, glazing and general building joints (available through trade hardware)
Soudal Glass and Glazing Silicone: neutral cure, glazing and window frames (Soudal Australia, verified 2026-05-11)

Properties

Property	Neutral cure (typical)	Acetoxy cure (typical)
Cure chemistry	Alcohol-release	Acetic acid-release
Skin time	10 to 40 min (colour-dependent)	5 to 13 min
Cure rate	~2 to 4 mm per 24 h at 23°C	~2 to 4 mm per 24 h at 23°C
Movement accommodation	±25% (standard), up to ±50% (premium grades)	±25%
Service temperature	-40°C to +150°C	-60°C to +175°C
Shore A hardness	~20 to 30	~20
Elongation at break	~200 to 500%	~500%
Paintable	No	No
Odour during cure	Low	Distinct (vinegar)
VOC	Low (GBCA compliant grades available)	Low to moderate

Grades and variants

Grade	Cure type	Where to use	Where NOT to use
Wet-area / sanitary	Neutral	Bathroom and kitchen tile joints, shower screen surrounds, bath and basin perimeters, splashbacks, plumbing penetrations	Permanent submersion; surfaces requiring paint finish
Glazing grade	Neutral or acetoxy	Window and door frame perimeter seals, structural glazing per AS 1288:2021	Natural stone surrounds (acetoxy only); copper or brass hardware adjacent joints
General purpose (GP)	Acetoxy	Glass-to-glass and glass-to-aluminium joints, general interior glazing, non-sensitive substrates	Natural stone, copper, brass, bituminous waterproof membranes, polypropylene, PTFE
Mould-resistant wet area	Neutral	Bathrooms, laundries, high-humidity kitchens	Same as wet-area grade; not a substitute for waterproofing membrane under tiles
AS 4020-rated	Neutral	Any joint in contact with potable water: kitchen bench to splashback, plumbing fixture surrounds	Refer to individual product TDS for exposure limits
Pool and spa	Neutral	Pool surrounds, spa shells, outdoor wet areas with permanent UV and chemical exposure	Not for use in drinking water lines without specific AS 4020 product approval

Where to use

Wet-area tile plane termination joints: the perimeter joint where tiled floor meets tiled wall, or wall tiles meet a bath or shower screen frame. Under AS 3740:2021 waterproofing requirements, these joints must accommodate movement without cracking the waterproof line. Neutral cure silicone is the compliant material in these locations.
Glazing perimeter seals: the joint between a window or door frame and the adjacent wall lining, and the glazing bead seat between glass and aluminium frame. AS 1288:2021 specifies structural silicone compliance for structural glazing applications.
Kitchen splashback perimeter: the joint at the top of a tile splashback where it meets the underside of overhead cabinetry, and at penetrations for electrical outlets. Where the joint is adjacent to a sink with potable water contact, use an AS/NZS 4020:2018-rated product.
Plumbing fixture surrounds: around basins, baths, shower bases, and toilet pedestal bases. Neutral cure only; confirm AS 4020 rating for potable water contact zones.
External window and door frame seals: joint between aluminium or timber frame and rendered or clad wall. Neutral cure for durability and UV resistance.

Where NOT to use

Over an existing bead: silicone does not bond reliably to cured silicone without full removal and primer. Tooling a new bead over an old one is a defect.
On natural stone with acetoxy cure: acetic acid etches marble, travertine, limestone, and similar calcite-based stone. Use neutral cure on all stone substrates.
On copper or brass adjacent surfaces: acetoxy cure corrodes copper and brass fittings. Neutral cure is required where fittings or adjacent hardware are copper-based.
On bituminous or coal-tar waterproofing membranes: acetic acid causes membrane bleeding and degradation. Neutral cure only on modified bitumen or asphaltic membranes.
In permanently submerged joints: no standard silicone sealant is rated for permanent water immersion. Use a purpose-rated pool or hydraulic sealant for below-waterline applications.
Where a painted finish is required: silicone sealants, both neutral and acetoxy, are not paintable once cured. For painted joint lines (skirting to wall, cornice, interior gaps), use a paintable MS polymer or acrylic sealant.
On PTFE, polyethylene, or polypropylene: silicone does not bond to these plastics without primer, and adhesion is unreliable even with primer.

Fixing and installation

Surface preparation

Clean, dry, and contaminant-free surfaces are mandatory. Remove any existing sealant fully with a sealant remover tool and solvent wipe. Tile grout must be fully cured (minimum 24 hours for cement grout, 72 hours for epoxy grout) before applying silicone adjacent to it. Dust, oils, soap residue, and form-release agents all cause adhesion failure.

Backing rod and joint sizing

For joints wider than 8 mm, install a closed-cell polyethylene backing rod to control bead depth. The standard joint geometry is width-to-depth ratio of 2:1. A 10 mm wide joint should have the sealant bead 5 mm deep. Oversized beads cure slower and can crack.

Application

Apply at 5 to 35°C. Cut the cartridge nozzle at 45 degrees to a diameter slightly smaller than the joint width. Apply in a single continuous pass, moving the gun at constant speed. Tool immediately with a wet finger or purpose tool within the skin time. Do not disturb curing bead after tooling.

Cure and protection

Do not wet the joint or expose to sustained moisture until the bead is fully cured (typically 24 to 48 hours for 10 mm bead at 23°C, 50% RH; slower in cold or low-humidity conditions). In a wet area, do not grout until the waterproofing membrane and any adjacent silicone joints have fully cured.

Tolerances and acceptance

Per current HIA Guide to Materials and Workmanship and the relevant state Guide to Standards and Tolerances. Verified numerical values for silicone sealant joint workmanship tolerances (acceptable bead width variance, tooling defects, adhesion failure criteria) in finished residential applications are pending HIA member access. [HIA-159]

Visual acceptance criteria for completed silicone joints:

Joint bead is continuous with no voids, gaps, or air pockets
Bead is smooth, concave-tooled, with clean edges at both substrates
No adhesion failure at either edge (lifting, peeling, or separation)
No sealant contamination on tile faces, glass, or frames (excess tooled off during application)
No discolouration or mould growth on fresh installation (mould resistant grade with fungicide)
Joint width consistent with design: deviation of more than 20% from specified width is a redo, not a patch

Working with other trades

Tiler: applies silicone at plane-change tile joints and perimeter joints in wet areas. Confirm grade (neutral cure mould resistant) and wait for membrane cure before sealing. Acetoxy near natural stone surrounds is a redo.
Glazier: selects glazing grade silicone to suit frame material and substrate. Structural glazing applications must use a silicone complying with AS 1288:2021 requirements.
Plumber: seals fixture surrounds and plumbing penetrations. AS/NZS 4020:2018 rated product required at any joint in contact with drinking water.
Builder / site manager: confirm the correct grade is on the work order before trades purchase product. Wrong grade on stone or copper, or unpaintable silicone used where a painted finish is expected, are PCI defects with a rework cost.

Health and safety

Acetic acid fumes (acetoxy cure)

Acetoxy silicone releases acetic acid vapour during cure. In enclosed bathrooms, shower enclosures, or internal glazing applications, ventilate with open windows or mechanical exhaust. Avoid prolonged inhalation. Workplace exposure standard for acetic acid (8-hour TWA): 10 ppm per Safe Work Australia (safeworkaustralia.gov.au, verified 2026-05-11).

Skin and eye contact

Uncured silicone sealant can cause skin irritation. Wear nitrile gloves. Eye protection for overhead or spray-adjacent applications. Uncured product in the eye requires immediate water flushing and medical attention. Once cured, silicone is chemically inert.

Solvents in surface preparation

Solvent wipes (acetone, isopropanol) used for substrate cleaning are flammable. Store away from ignition sources. Use in ventilated spaces. Dispose of solvent-soaked rags in a sealed metal bin.

Suppliers

Selleys (selleys.com.au): Wet Area Silicone (neutral cure, mould resistant), Pro-Trade Wet Area Silicone (neutral cure, low VOC, GBCA). Available at Bunnings, Mitre 10, trade merchants nationally.
Sika Australia (aus.sika.com): Sikasil-702 (neutral cure, AS 4020 rated, 15 colours), SikaSeal Kitchen and Bathroom (neutral cure, AS 4020 compliant), Sikasil-GP (acetoxy, general purpose). Available at Bunnings and trade suppliers.
Soudal Australia (soudal.com.au): Glass and Glazing Silicone (neutral cure), range of sanitary and exterior grades. Available through trade hardware.
Davco (distributed via Sika): Davco N Silicone (neutral cure sanitary grade). Available through tile and trade suppliers.

[Sponsor / preferred installer slot. ACCC disclosure required.]

What can go wrong

Applying over existing sealant: silicone does not bond to cured silicone. The new bead peels at the edges within months. Full removal is the only fix.
Acetoxy on stone or copper: irreversible acid etch on marble, travertine, or limestone; corrosion on brass and copper hardware. Wrong product choice costs a full substrate refinish or fitting replacement.
Using silicone where paint is required: silicone is not paintable. A painted line over silicone peels off the sealant within weeks. Specify an acrylic or MS polymer sealant for any joint that will be painted.
Skipping backing rod on wide joints: a too-deep bead of silicone cures slowly through its centre, leaving a soft core that splits under movement. Joint design matters.
Sealing grout joints instead of movement joints: applying silicone in grout joints mid-tile is not a substitute for the dedicated plane-change movement joints. Movement will crack both the grout and the tile.
Applying in cold or dry conditions without allowance for extended cure: at 10°C and low humidity, a 10 mm bead can take 3 to 4 days to cure through. Wetting the joint (shower use) before full cure causes adhesion failure and early mould growth.
Mould before cure: silicone mould resistance is effective once cured. Applying in a humid environment without adequate ventilation before cure allows mould spores to embed in the uncured bead.

References

Selleys Australia, Wet Area Silicone product page (selleys.com.au) (verified 2026-05-11)
Selleys Australia, Pro Trade Wet Area Silicone product page (selleys.com.au) (verified 2026-05-11)
Sika Australia, Sikasil-702 product page, AS/NZS 4020:2018 compliance confirmed (aus.sika.com) (verified 2026-05-11)
Sika Australia, SikaSeal Kitchen and Bathroom product data sheet (aus.sika.com) (verified 2026-05-11)
Soudal Australia, Glass and Glazing Silicone product page (soudal.com.au) (verified 2026-05-11)
Quality Seal Australia, Acetoxy vs Neutral Cure Silicone (qualitysealaustralia.com.au) (verified 2026-05-11)
Sealem Solutions Australia, Silicone vs Polyurethane Sealants (sealemsolutions.com.au) (verified 2026-05-11)
AS/NZS 4020:2018, Testing of products for use in contact with drinking water, Standards Australia
AS 1288:2021, Glass in buildings: selection and installation, Standards Australia
AS 3740:2021, Waterproofing of domestic wet areas, Standards Australia
Safe Work Australia, Workplace exposure standards for airborne contaminants (safeworkaustralia.gov.au) (verified 2026-05-11)