GacoFlex S42 is a 96.5% solids silicone roof coating system supplied by Duratite as the exclusive UK distributor. It is engineered to waterproof and restore aged commercial roof substrates — including asphalt, EPDM, GRP, single-ply, asbestos cement and metal — under a 20-year manufacturer-backed product warranty.
Why specify GacoFlex S42 silicone roof coating
GacoFlex S42 is a 96.5% solids silicone roof coating (by weight; 95% by volume). It is manufactured by Amrize (formerly Holcim Building Envelope) and supplied in the UK exclusively through Duratite Building Products Limited. The 96.5% solids formulation delivers minimal shrinkage and high yield — a single 18.9 L pail covers approximately 32 m² at 0.43 mm wet-film thickness (10-year specification), or 16 m² at 0.86 mm WFT (20-year specification).
Independently confirmed performance data on the system includes tensile strength of 450 psi (ASTM D412), elongation at break of 169% at -18°C (ASTM D412), and initial solar reflectance of 0.88 (ASTM C1549). The white finish carries Cool Roof Rating Council (CRRC) listing and Energy Star listing. The system is UL Listed, holds a published Environmental Product Declaration (EPD), and tests to ASTM D6694 — the silicone roof coating standard.
GacoFlex S42 is fibre-reinforced — it does not require a separate fabric or mesh reinforcement layer. Service temperature range is -45°C to +150°C, covering the full UK ambient and surface-temperature range. VOC content is 37 g/L (EPA Method 24), compliant with UK and EU regulations.
Application and system specification
A typical UK GacoFlex S42 installation begins with a substrate adhesion test, followed by surface cleaning with GacoWash and high-pressure rinsing. Seams, penetrations, fasteners and cracks are detailed with GacoFlex SF42 silicone seam sealant or GacoPatch repair compound. On asphalt or modified-bitumen substrates, GacoFlex A4271 Bleed Trap Base Coat is applied first to prevent oil migration through the silicone topcoat.
GacoFlex S42 itself is applied at a minimum 2.25 gallons per 100 sq ft to achieve a 34-mil dry film thickness. For 10-year warranty specification this is delivered as a single coat at 0.43 mm WFT; for 20-year specification, a two-coat system at 0.86 mm WFT total. Different-coloured base and top coats (typically white then grey) verify total coverage visually and prevent sag on sloped surfaces.
Specification documents, datasheets and warranty schedules are supplied with every Duratite quote, alongside the project method statement and risk assessment. Duratite is the UK product authority — Duratite Building Products Limited issues manufacturer statements directly on its own letterhead for warranty and handover purposes.
Warranty and certification
GacoFlex S42 carries a 20-year manufacturer-backed product warranty when applied to the 0.86 mm two-coat specification. The warranty is issued by Duratite Building Products Limited (Co. No. 15897144; VAT 475375459). Where Duratite Projects Limited (Co. No. 09789966; VAT 232318243) performs the installation, a separate workmanship warranty is issued alongside.
The warranty is manufacturer-backed —. The product is supported by a published Environmental Product Declaration (EPD), UL Listed status, CRRC cool-roof listing, Energy Star listing, and ASTM D6694 test data (the silicone roof coating standard).
Pricing depends on substrate condition, access difficulty and total project area. Every project quote includes free site survey, substrate adhesion testing, and a fixed written specification. Call 01208 832 602 for a quote response or request a free survey online.
Frequently asked questions
Is GacoFlex S42 suitable for ponding water?
Yes. The silicone chemistry is engineered for ponding-water resistance. This is one of the primary reasons silicone is specified over acrylic systems on UK commercial roofs.
Can S42 be installed over existing asphalt, felt, metal or asbestos cement roofs?
Yes. The system is approved for application over aged Built-Up Asphalt, Modified Bitumen (SBS/APP), EPDM and TPO single-ply membranes, PVC and Hypalon, GRP / fibreglass, asbestos cement and fibre cement roof sheets, and corrugated or standing-seam metal roofs. Substrate suitability is confirmed by adhesion testing during the free survey.
What is the published solar reflectance value for the white S42?
Initial solar reflectance is 0.88 (ASTM C1549), placing the white finish in the Cool Roof Rating Council (CRRC) listed range.
What's the service temperature range?
-45°C to +150°C, covering the full UK ambient and surface-temperature range without softening or losing adhesion.
Is GacoFlex S42 BBA certified?
No. GacoFlex products are not BBA certified — they rely on UL Listed status, CRRC listing, Energy Star listing, ASTM D6694 test data, and a published EPD. (Our group company ThermoHoldings Ltd holds BBA Agrément Certificates 23/6963 and 23/6845, covering Enverge Nexseal LE and Sucraseal spray foam in domestic buildings — different products.)
How does the warranty work — what's covered and for how long?
The system carries a 20-year manufacturer-backed product warranty issued by Duratite Building Products Limited when applied at the 0.86 mm two-coat specification. Where Duratite Projects Limited performs the installation, a separate workmanship warranty is issued alongside.
Does S42 need a separate fabric or mesh reinforcement layer?
No. GacoFlex S42 is fibre-reinforced — it does not require a separate scrim or fleece. Detail-coats at seams, fasteners and penetrations use GacoFlex SF42 silicone seam sealant or GacoPatch repair compound.
How do I book a free survey?
Call 01208 832 602 or request a free site survey through duratite.co.uk. A trained Duratite specialist will visit the property, perform substrate adhesion testing, photograph the existing condition, and produce a written specification + fixed quote.
