The Complete Guide to Silicone Roof Coatings in the UK
Your flat roof is one of the most exposed components of any building — and in the UK, it takes a constant battering from rain, wind, UV, and temperature swings. When the waterproofing starts to fail, the consequences are swift: leaks, damp, disrupted operations, and the very real prospect of a six-figure re-roofing bill. A high-performance silicone roof coating can stop that cycle before it starts — and in many cases, extend the life of an existing roof by 20 years or more.
This guide covers everything facility managers, building owners, and roofing contractors need to know about silicone roof coatings in the UK: how they work, when to use them, how they compare to alternatives, and what the application process looks like. Duratite is the UK's exclusive distributor of GacoFlex silicone roof systems by Amrize — including the flagship GacoFlex S42 and fibre-reinforced SF42.
What Is a Silicone Roof Coating?
A silicone roof coating is a liquid-applied waterproofing membrane that cures to form a seamless, permanently flexible, and fully bonded layer over your existing roof surface. Unlike sheet membranes or bituminous felt, there are no laps, seams, or joints — the areas where virtually all flat roof failures originate.
The chemistry is what sets silicone apart from other liquid roof coating technologies. Silicone polymers are inherently UV-stable, non-absorptive, and remain elastic across a wide temperature range. In the UK climate — freeze-thaw cycles in winter, intense UV in summer — that combination of properties makes silicone the most durable roof coating chemistry available.
GacoFlex silicone coatings from Amrize are moisture-cure systems: they react with atmospheric humidity to form a tough, rubber-like membrane that bonds permanently to the substrate. Once cured, the coating will not crack, chalk, or degrade — even after decades on the roof.
GacoFlex S42 and SF42 — Duratite's Flagship Systems
Duratite supplies two core silicone flat roof coating systems for the UK market:
GacoFlex S42 — Standard Silicone
GacoFlex S42 is a single-component, 100% silicone roof waterproofing coating. It achieves full waterproofing performance in a single coat — typically at 20 mils (0.5mm) DFT. Key performance characteristics:
- Permanent ponding water resistance — silicone does not absorb water and will not blister, soften, or delaminate under standing water. This is the critical differentiator on UK flat roofs, where adequate falls are not always achievable
- UV stability without chalk or fade — the silicone molecular backbone does not break down under UV exposure; the coating maintains its properties and appearance without cracking or chalking
- Remains flexible at sub-zero temperatures — accommodates thermal movement without splitting
- Bonds to most existing substrates without a primer — bitumen, asphalt, single-ply, felt, metal, concrete, and GRP all accept S42 direct
- 20-year warranty available — when applied by a Duratite-approved contractor to a prepared substrate
GacoFlex SF42 — Fibre-Reinforced Silicone
GacoFlex SF42 shares the same silicone chemistry as S42 but incorporates reinforcing fibres directly within the coating matrix. This is an important distinction: SF42 does not require a separate reinforcing fabric or mesh to be laid — the fibre reinforcement is integral to the product.
SF42 is the preferred specification for roofs with:
- Existing cracks, splits, or surface irregularities that need bridging
- Higher movement risk (large buildings, exposed locations, or roofs spanning wide structural bays)
- Aged bitumen or asphalt where surface condition is variable
- Any situation where additional tensile strength is specified by an engineer or surveyor
In practice, many commercial projects specify SF42 as the default, particularly for re-coating aged built-up roofing systems. The added reinforcement adds minimal cost but substantially increases confidence in long-term performance.
Silicone vs Alternatives — How Does It Compare?
The UK market offers several liquid applied roof coating technologies. Here is how silicone compares against the main alternatives:
| Property | Silicone (S42/SF42) | Acrylic | Polyurethane |
|---|---|---|---|
| Ponding water tolerance | Excellent — permanent | Poor — absorbs water, can delaminate | Good |
| UV resistance | Excellent — no chalk or fade | Good — some chalking over time | Moderate — can yellow and chalk |
| Flexibility at low temperatures | Excellent | Moderate | Good |
| Warranty period | Up to 20 years | 10–15 years | 10–15 years |
| Application coats | Single coat | Two coats typically | Two coats typically |
| Relative cost | Mid to premium | Lower | Higher |
For UK commercial roofs — where standing water is common due to inadequate falls or blocked drainage — silicone's superior ponding water tolerance makes it the technically correct specification in the majority of cases. Acrylic coatings, while cost-effective, are not suitable for any roof where water can collect.
Coating vs Full Replacement — How to Decide
One of the most common questions we receive is whether a roof needs to be coated or replaced entirely. The honest answer depends on the condition of the substrate beneath the existing weathering surface.
A silicone roof coating is appropriate when:
- The roof deck (concrete, steel, timber) is structurally sound
- The insulation layer is dry — confirmed by a moisture survey
- The existing surface has weathered, cracked, or begun to leak, but is broadly intact
- The building is operational and a full strip-out would cause disruption
Full replacement is necessary when:
- The insulation has become saturated (typically identified by thermal imaging or core sampling)
- The roof deck has structural damage, rot, or corrosion
- There is widespread delamination across the whole roof area
- The building specification requires a significant uplift in insulation performance
Duratite carries out no-obligation roof surveys to give you an accurate assessment. In our experience, the majority of commercial flat roofs presenting with leaks are suitable for coating — not replacement. The existing roof stays in place — no tear-off, no waste to landfill, and no disruption to the building below — with comparable longevity.
The Application Process
A GacoFlex silicone roof coating project follows a consistent process whether the roof is 200 m² or 20,000 m²:
- Survey and specification — Duratite surveys the roof, identifies any structural or moisture issues, and specifies the correct product and application rate
- Surface preparation — the existing surface is pressure-washed clean. Any loose material, moss, algae, or contamination is removed. Splits, blisters, and open joints are repaired with compatible sealant or reinforcing tape
- Priming (where required) — most substrates accept S42 or SF42 direct, but certain surfaces (galvanised metal, some single-ply membranes) require a compatible primer coat first
- Coating application — GacoFlex S42 is applied at the specified mil thickness by brush, roller, or spray. SF42 is applied in the same way — no separate reinforcing step required. For most commercial projects, this is a single coat to the full specification rate
- Inspection and sign-off — wet film thickness is checked during application; dry film thickness is confirmed on completion. Warranty documentation is issued on approval
For most commercial buildings, the entire process — from survey to completion — is carried out without the building needing to close or vacate. Works are typically completed within 1–5 days depending on roof size.
Warranty Options
GacoFlex silicone systems are available with manufacturer-backed warranties of up to 20 years when applied by a Duratite-approved contractor. Warranty options are typically structured as:
- 10-year material warranty — covers defects in the coating material itself
- 15-year system warranty — covers material and workmanship when applied by an approved installer
- 20-year full system warranty — covers material, workmanship, and watertight performance; requires a pre-application survey and post-application inspection sign-off
For facilities managers and building owners responsible for long-term asset maintenance, the 20-year warranted system provides a clear and auditable record of roof performance obligations — important for both insurance and lease compliance purposes.
Frequently Asked Questions
How long does a silicone roof coating last in the UK?
GacoFlex silicone roof coatings are warranted for up to 20 years when correctly applied to a properly prepared substrate. Silicone does not degrade under UV exposure and will not crack, chalk, or peel over time. With periodic inspection and minor maintenance, coated roofs routinely outlast the warranty period.
Can silicone roof coating be applied over an existing flat roof?
Yes. GacoFlex S42 and SF42 bond directly to most existing roof substrates — including aged bitumen, asphalt, single-ply membranes, felt, metal, concrete, and GRP — without stripping the existing surface. The roof must be structurally sound, clean, and dry. Minor repairs to splits and blisters are carried out before coating.
What is the difference between GacoFlex S42 and SF42?
GacoFlex S42 is a 100% silicone coating applied as a single coat. GacoFlex SF42 is a fibre-reinforced variant of the same chemistry — the fibres are integral to the coating itself, so no separate reinforcing fabric or mesh is required. SF42 is preferred for roofs with cracks, surface irregularities, or higher movement risk.
When should I coat my roof rather than replace it?
A coating is the right choice when the existing substrate is structurally sound but showing weathering, minor cracking, or early leaks. If the insulation is saturated or the deck is structurally compromised, replacement is necessary. A Duratite survey will give you an honest assessment — call 01208 832602 to arrange one.
How much does silicone roof coating cost in the UK?
Supply-and-fit costs for GacoFlex silicone typically range from £40 to £60 per m², depending on roof size, condition, access, and specification. The existing roof stays in place — no tear-off and no waste to landfill — and the system carries a 20-year manufacturer-backed product warranty. Supply-only pricing for approved contractors is available on request.
Speak to the Duratite Technical Team
Duratite is the UK's exclusive distributor of GacoFlex silicone roof coatings by Amrize. We supply nationwide and operate an approved installer network across the UK — which means you can source the product, the expertise, and the warranty under one roof.
Whether you are a facilities manager assessing your options, a building owner planning a maintenance programme, or a roofing contractor looking for a reliable supply and technical partner, we can help.
Call us on 01208 832602 to speak with a member of the technical team, or visit duratite.co.uk/contact to request a survey or supply enquiry.
