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For tiled wet areas, kitchens, and bathrooms where a reflective gloss bead would disrupt the design, Matt Seal S-350 Sanitary Silicone Sealant provides a clean, matte finish that resists fungal growth in hot and humid environments. This neutral-curing silicone accommodates high joint movement while protecting joints from mould, making it suitable for both residential bathrooms and demanding commercial installations.
Matt Seal S-350 is a neutral (oxime) curing silicone formulated with an added fungicide to inhibit mould and biological growth. On exposure to atmospheric humidity, it cures to form a permanently flexible, dustproof, and waterproof joint seal. It is non-corrosive to galvanised steel, zinc-coated steel, and concrete. Because the cured rubber maintains excellent UV stability and colour fastness, it can be used for internal and external seals, including areas under permanent UV exposure.
Matt Seal S-350 forms a bond across common building substrates, including:
It is suitable for joints in shower walls and floors, commercial kitchens, laundries, steam and spa rooms, plumbing and roofing seals, shopfitting, vehicle fabrication, and marine applications. Once cured, it is suitable for below-waterline applications in marine environments.
For optimal movement performance, design joints to a 2:1 width-to-depth ratio. Internal joints require a minimum width and depth of 5mm. External joints require a minimum width of 10mm. The maximum joint width is 30mm, and the maximum depth is 15mm. Use a closed-cell backing rod 25% larger than the joint width for joints deeper than 10mm to prevent three-sided adhesion.
Apply the sealant at temperatures between 5°C and 40°C on clean, dry substrates. Ensure concrete has cured for at least 28 days to prevent moisture-driven delamination or mould growth. Use a two-wipe process with Acetone or 100% White Spirits on non-porous surfaces. Tool the bead with a moistened spatula within 15 minutes before the skin forms, and remove any masking tape while the sealant is still wet.
Matt Seal S-350 provides a low-sheen finish that integrates with common grout lines in tiled wet areas. Its anti-fungal properties actively inhibit mould and biological growth, preventing common failures and callbacks in bathrooms, kitchens, and laundries.
Matt Seal S-350 is not recommended for all stone without prior stain testing due to potential discolouration. It is also not paintable; ensure masking is used to keep application clean. For adhering mirrors or structural glazing, Adheseal offers alternative specialised products.
For internal joints, maintain a minimum width and depth of 5mm. External joints require a minimum of 10mm width and depth. Always aim for a 2:1 width-to-depth ratio and use a backing rod for depths over 10mm to ensure proper movement capability and prevent three-sided adhesion.
| Application | Key benefit | Primary trades |
|---|---|---|
| Joint sealing in shower walls and floors, commercial kitchens and laundries, steam and spa rooms | Actively inhibits mould and biological growth with added fungicide. Maintains a waterproof, flexible seal in hot, humid environments. The matt finish blends with tiled surfaces. | Tilers, Plumbers, Bathroom Renovators |
| Construction joints, air conditioning, general plumbing and roofing sealing, shopfitting | Offers ±25% movement capability, maintaining seal integrity against building movement. UV stable and colour fast for exterior exposure. Neutral (oxime) cure protects sensitive metals like galvanised steel. | Builders, Plumbers, Roofers, Shopfitters, HVAC Installers |
| Marine and boat building, vehicle fabrication, sealing electrical installations | Once cured, it is suitable for below-waterline applications. High permanent flexibility handles dynamic movement. Low odour and non-corrosive to common metals. | Marine Fabricators, Vehicle Manufacturers, Electricians |
Ensure ventilation is adequate to maintain air concentrations below exposure standards. Use only in well-ventilated areas.
Store in a cool, dry, well-ventilated place, out of direct sunlight and away from foodstuffs or incompatible materials. Keep containers closed and upright. Dispose of cured rubber according to local regulations.
Good adhesion is critical for long-term performance. Proper surface preparation ensures the sealant bonds correctly and performs as expected.
Surface prep: Surfaces must be structurally sound, dry, and clean. Remove all dust, oils, grease, and other contaminants. For impervious surfaces, use the two-wipe process with Acetone or 100% White Spirits, changing cloths frequently.
Primer: Not required for most applications. For optimal adhesion in highly stressed joints, priming with 50A surface prep is advised for non-porous surfaces.
Surface prep: Surfaces must be sound, dry, and clean, free of dust, oils, grease, or contaminants. Concrete must be allowed to cure for at least 28 days to prevent mould growth and ensure adhesion.
Primer: Not required for most applications. For optimal adhesion on porous surfaces in highly stressed joints, Supaprime primer is advised.
Surface prep: Surfaces must be sound, dry, and clean, free of dust, oils, grease, or contaminants. For impervious surfaces, use the two-wipe process with Acetone or 100% White Spirits. This neutral cure silicone will not corrode galvanised or zinc-coated steel.
Primer: Not required for most applications. For optimal adhesion in highly stressed joints, priming with 50A surface prep is advised for non-porous surfaces.
| Property | Value |
|---|---|
| Product Type | Polysiloxanes |
| Curing System | Oxime (Neutral Cure) |
| Specific Gravity (23°C) | 1.45 |
| Shore A Hardness | 20 |
| Elongation at Break | 300% |
| Elastic Recovery | >90% |
| Movement Capability | ±25% |
| Application Temperature | +5°C to +35°C |
| Temperature Resistance | -50°C to +150°C |
| Skin Time | Approximately 15-20 minutes |
| Cure Rate | 2mm per day (at 25°C & 50% RH) |
| VOC Content | 30 g/Litre |
| Flash Point | >93°C |
Here are some common examples on where Matt Seal S-350 Sanitary Silicone Sealant used by our customers.
