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shop@flatroofingsystems.co.ukGacoFlex SF42 Silicone Seam Sealant – 18.9 Litres
Manufacturer/Brand: Gaco
SKU:SF4200-5
In stock
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Seal roof seams, laps, upstands and fixings with GacoFlex SF42, a fibre-reinforced silicone sealant designed for detailing work within the GacoFlex silicone roof system. Supplied in an 18.9 litre pail in White, it creates a waterproof, flexible seal before the roof is coated with GacoFlex S42.
Also known as GacoFlex SF4200 SeamSeal, SF42 combines a high-adhesion silicone sealant with built-in reinforcement. Routine seams and details can be treated without bedding in a separate scrim or mesh, simplifying preparation of these areas.
The solvent-free, single-component formulation moisture-cures to form a waterproof, elastomeric seal.
Key Features:
- Built-in fibre reinforcement – no separate scrim or mesh required for routine seams and details.
- Solvent-free and single-component – no separate hardener to mix.
- Moisture-curing silicone – forms a flexible, waterproof seal.
- Excellent system adhesion – adheres to GacoFlex silicone coatings and GacoFlex A4271 Bleed Trap base coat.
- Versatile detailing product – suitable for seams, laps, flashings, upstands and roof fixings.
- Durable finish – offers good colour stability and resistance to chalking.
Suitable Applications:
GacoFlex SF42 is used as a flashing material and joint and fastener sealant before applying the main GacoFlex S42 roof coating. Typical applications include:
- Seams and overlapping joints on metal roofs.
- Roof fasteners and fixings.
- Flashings and upstands.
- Localised repairs to compatible roof surfaces.
- Filling cracks in smooth built-up roofing.
Gaps wider than 6mm require embedded fabric reinforcement. Always follow the specified detail and current manufacturer’s application instructions.
Pail Size, Colour and Coverage
- Product - GacoFlex SF42 / SF4200 SeamSeal.
- Type - Fibre-reinforced silicone seam sealant.
- Pail size - 18.9 litres.
- Colour - White.
- Approximate coverage - 223 linear metres of seam per pail.
- Curing method - Moisture-curing.
Coverage is approximate and will vary depending on seam width, application thickness, surface condition and the complexity of the details being treated.
Preparation and Application
Surfaces must be sound, clean and suitably prepared before application. Apply SF42 to the required seams, laps, fasteners and details in accordance with the GacoFlex system specification before coating the roof with GacoFlex S42.
Check the current technical data sheet for substrate compatibility, preparation requirements, application conditions and curing times.
Order GacoFlex SF42 Silicone Seam Sealant from All Flat Roofing Supplies, with UK-wide delivery.
Additional Information for GacoFlex SF42 Silicone Seam Sealant – 18.9 Litres
Delivery Information
Delivery Information
Gaco roof coatings are delivered directly to your chosen address through our network of courier and pallet delivery services. Delivery typically takes 1–3 working days, although remote locations and busy periods may require slightly longer. Delivery times are estimates and cannot be guaranteed.
Please advise us before dispatch of any access restrictions, road closures or other circumstances that could prevent or delay delivery. Delivery vehicles may range from small vans to rigid and large articulated HGVs. We cannot control which vehicle is allocated to your order.
We strongly recommend that you do not schedule roofing works until your order has been received in full and checked.
Checking Your Delivery
Please inspect your order on arrival. Any visible damage should be recorded on the delivery paperwork, and any damaged items must be reported to our office within 48 hours of delivery. Photographs of the packaging and affected products will help us resolve the matter promptly.
Tins may occasionally become dented or distorted during transport. Cosmetic dents do not normally affect the contents or their suitability for use, provided the tin remains sealed and intact, we would not normally refund or exchange. If a tin is split, leaking, open or has a damaged seal, please report it as a damaged item.
Returns Information
Returns are accepted within 14 days of delivery. Please contact our office before returning any products so we can confirm the correct procedure and return address. The return address may differ from our operational depot.
Products must be unused, unopened and in their original condition. For change-of-mind returns, you are responsible for the return delivery costs and for ensuring the goods are securely packaged.
Returned goods remain your responsibility until they have been received and inspected by our customer service team. We recommend using a tracked delivery service with suitable cover for the value of the goods. We cannot refund items that are missing from the return or arrive damaged.
These conditions do not affect your statutory rights, including those relating to faulty, damaged or incorrectly supplied goods.
FAQ's
What is GacoFlex SF42 Seam Sealant used for?
GacoFlex SF42 is used to waterproof seams, laps, fixings, flashings and upstands before applying GacoFlex S42 Silicone Roof Coating. It is the detailing product within the GacoFlex silicone roof system.
Do I need to use reinforcing mesh with SF42?
SF42 contains built-in fibre reinforcement, so separate scrim or mesh is not required for routine seams and details. However, gaps wider than 6mm require embedded fabric reinforcement, in accordance with the manufacturer’s instructions.
Can SF42 be used instead of GacoFlex S42 roof coating?
SF42 is designed for sealing joints and roof details. GacoFlex S42 is the main waterproofing coating applied across the roof surface. The two products perform different roles within the system.
How much does one pail cover?
An 18.9 litre pail treats approximately 223 linear metres of seam. Actual coverage depends on the width and thickness of application, surface condition and the details being sealed.
Does GacoFlex SF42 need mixing with a hardener?
No. SF42 is a single-component, moisture-curing silicone sealant and does not require a separate hardener. Always follow the current technical data sheet for preparation and application instructions.