Services / GRP Roofing

    GRP Flat Roof Alternative

    Considering GRP fibreglass? We install the Ultraflex cold-liquid system instead. It bonds seamlessly over GRP and most other substrates, cures rapidly, eliminates fire risk on site and comes with a 20-year guarantee. It's the best-kept secret in flat roofing.

    • Cracks and crazing
    • Leaks at joints and edges
    • UV and weather damage
    • Costly repairs
    Instant Estimate
    Common problems

    The problems with GRP flat roofs

    GRP fibreglass looks great on day one, but it's a rigid, multi-layered system that doesn't move with your building, and once it fails, repairs rarely hold.

    • Cracks and crazes over time

      GRP is brittle. Thermal movement, foot traffic and building shift cause hairline cracks, star fractures and crazing, especially around edge trims and detailing.

    • Multi-layer system with weak points

      Topcoat, matting, resin and trims are all separate layers. A single failure in a bond, trim or seam lets water through to the deck below.

    • Weather and UV degradation

      UV slowly breaks down the topcoat, causing colour loss, chalking and surface erosion. Standing water accelerates the damage.

    • Poor flexibility on complex details

      Upstands, pipes, rooflights and corners are GRP's weakest points. Rigid laminate struggles to wrap detailing cleanly, leading to leaks.

    • Difficult, costly repairs

      Once GRP fails it usually means cutting out and re-laminating sections, or a full strip and re-lay. Patch repairs rarely last.

    Cracked, crazed GRP fibreglass flat roof showing weather damage
    GRP vs Perlini System

    Why we install our waterproofing system over GRP

    GRP is rigid, prone to cracking around detailing, and once it fails, it usually means a full re-lay. Our waterproofing system is a flexible, cold-applied liquid membrane that moves with the building, wraps complex details without joints, and can even be installed straight over an existing GRP roof, backed by a 20-year guarantee.

    Same roof overlaid with seamless Ultraflex membrane
    Close-up of a GRP fibreglass flat roof with edge trim
    BeforeAfter
    Powered by Ultraflex

    One of the best flat roof waterproofing systems on the market

    Whatever flat roof job you have (installation, repair, replacement, or an asphalt, GRP, EPDM or torch-on felt overlay), we install the Ultraflex cold-liquid waterproofing system. It's the most durable, cost-effective, and reliable flat-roof solution available.

    By overlaying your existing roof with Ultraflex, we save you the cost and disruption of a full strip-out while delivering a fully bonded, seamless waterproof layer backed by a 20-year guarantee. We go in, repair your existing roof and seal it for decades of protection. If needed, we can apply bespoke finishes and solutions post-waterproofing.

    Ultraflex flat roof installation

    Why we install Ultraflex on every job

    Faster installation

    Fast-curing and rainproof in as little as 30 minutes.

    Up to 50% cost savings

    Overlay your existing roof and avoid strip-out costs.

    20-year guarantee

    Proven waterproofing built for long-lasting protection.

    100% Compatible

    Torch-on felt, asphalt, GRP, timber, concrete, and virtually any roof surface.

    Safer installation

    Cold-liquid application, eliminating fire risk.

    Seamless waterproofing

    No joints or laps, just one fully bonded waterproof layer.

    How we work

    1. 1

      Instant Estimate

      Fill out our cost estimate tool to receive a fast, ballpark price based on your project details. It's a quick way to understand likely costs before moving forward.

    2. 2

      Site Visit + Detailed Quote

      We carry out a site visit where needed to assess your roof in detail, then provide a clear, itemised quote with no hidden costs so you know exactly what to expect.

    3. 3

      Installation

      Our trained team prepares the surface and installs the Ultraflex system, delivering a seamless, fully bonded waterproof finish built to last.

    4. 4

      Sign-off & 20 Year Guarantee

      We inspect the roof, hand over your 20-year guarantee documentation, and leave the property spotless.

    How Ultraflex compares

    See how our Ultraflex cold-liquid waterproofing system stacks up against traditional flat roof systems across the things that matter most.

    CriteriaUltraflexGRPEPDMAsphaltFelt
    Seamless, fully bonded
    Yes
    Yes
    No
    No
    No
    Cold-applied (no flame)
    Yes
    Yes
    Yes
    No
    No
    Rainproof in 30 minutes
    Yes
    No
    No
    No
    No
    Overlay existing roof
    Yes
    No
    No
    No
    Yes
    20-year guarantee
    Yes
    Yes
    Yes
    No
    Yes
    Cost-effective long-term
    Yes
    No
    Yes
    No
    No
    Resists cracking & shrinking
    Yes
    No
    Yes
    No
    No
    Suitable for complex detailing
    Yes
    Yes
    No
    No
    No

    Ultraflex typically costs in line with or less than a quality GRP installation, with faster curing, no fire risk and a 20-year guarantee. Use our estimator for a personalised quote.

    Ultraflex FAQs

    The most common questions we get asked about the Ultraflex cold-liquid waterproofing system.

    A well-specified GRP roof laid over a correctly built deck can give twenty years or more. In practice we see many crack much earlier, usually because the deck was too thin or insufficiently supported, or because the laminate was applied to damp boards or in unsuitable weather. Crazing around trims and over board joints is the earliest warning sign.

    Yes. Once the surface has been abraded, cleaned, made good and primed for a polyester substrate, the liquid system bonds well to GRP. This is normally far cheaper and less disruptive than cutting out the laminate and the deck below it.

    Nearly always because of movement in the deck. Boards that are too thin, joists at too wide a spacing, inadequate noggins at board edges, or laminating over boards that had not fully dried will all produce early cracking, typically over the board joints and at the internal corners of upstands.

    A liquid system generally handles trafficked balconies and terraces better, because the detailing around thresholds, drainage channels and balustrade posts is formed in one continuous membrane rather than laminated in sections. Anti-slip surfacing can be built into the finish where the area is walked on regularly.

    GRP installation releases a strong styrene odour that carries a long way and often draws complaints on terraced streets. The Ultraflex resins are low odour by comparison and cure far faster, so any smell is short lived, and there is no hot work or flame involved at any stage.

    We can, and sometimes that is the sensible short-term answer. But a crack is a symptom of movement, and a rigid patch simply relocates the stress to its own edge, so localised GRP repairs commonly fail again within a season or two. Overlaying the whole roof with a flexible membrane deals with the movement rather than the crack.

    Services tailored to your flat roof, we work on any job.

    From new installations and full system refurbishments to targeted leak diagnostics and repairs, every project is carried out by our in-house specialists using premium, manufacturer-approved liquid waterproofing systems.

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