Ultraflex PU is a professional-grade liquid waterproofing system that has been quietly building a strong reputation among roofing contractors and specifiers across the UK.
Whether you're waterproofing a new flat roof, refurbishing an ageing felt deck, or tackling a complex balcony or car park detail, Ultraflex is engineered to handle it.
Here are the questions we're most commonly asked about the system.
What is Ultraflex PU Liquid Waterproofing?
Ultraflex PU is a high-performance, single-component solvent-based polyurethane liquid membrane manufactured by Eagle Waterproofing's parent brand, UltraPolymers - a company with over 35 years of experience formulating liquid waterproofing systems and exporting to five continents.
It is designed for professional installation on both new-build and refurbishment projects. Applied as a liquid, it cures to form a seamless, continuous, elastomeric membrane. Used in conjunction with Ultraflex reinforcement matting, the system creates a fully reinforced waterproofing layer that bonds directly to the substrate with no joints, seams, or laps.
Ultraflex is moisture-curing and requires no catalyst or hardener for standard application — simply stir and apply. It is BBA and ETE certified for a service life in excess of 25 years, and is also NHBC and Green Roof approved.
What Makes Ultraflex Different from Other Liquid Waterproofing Systems?
Several things set Ultraflex apart from competing liquid membrane systems.
No mixing required for standard use. Ultraflex is ready to use straight from the drum -no catalysts, no measuring, no risk of mixing errors on site. This reduces waste and speeds up installation significantly.
No primer needed on most surfaces. Unlike many liquid systems, Ultraflex bonds directly to the vast majority of common roofing substrates without a primer coat, saving both time and material cost.
The wet-on-wet reinforcement method. Ultraflex Matting is a fibreglass chop-strand matting specially formulated so that its resins activate on contact with the Ultraflex liquid membrane. This means the matting and liquid chemically bond together to form a monolithic, fully reinforced membrane -not just a laminated layer. Critically, once the matting is fully encapsulated, the roof is immediately showerproof, even before the membrane has fully cured.
Flexibility to extreme cold. Ultraflex has been tested down to -35°C and maintains its physical properties without cracking or delaminating - important for UK roofing applications where freeze-thaw cycling is a real concern.
Quickcure additive option. For time-sensitive applications - balconies, communal walkways, or areas that need to be returned to use quickly -Quickcure can be mixed into the drum to accelerate curing. With Quickcure, drying time reduces to approximately 2 hours and heavy traffic is possible within 24 hours.
What Surfaces Can Ultraflex PU Be Applied To?
Ultraflex is formulated for excellent adhesion across a broad range of substrates. No primer is required on most standard roofing materials. It bonds effectively to plywood and OSB, torch-on and bitumen membranes, asphalt, metal roofing, concrete (cured for a full 28 days), brick, single ply membranes, GRP, ceramic tiles, corrugated sheet (including asbestos with Tixal additive for pitched surfaces), and wood.
On EPDM and TPO substrates, a compatibility patch test is recommended before full application. On rough or porous concrete, Ultraprime Pro primer can be used to improve yield and reduce product consumption.
Important: Silicone sealants must never be used with Ultraflex. Always use Ultraflex Sealant (a modified silane MS polymer) or another compatible PU-based mastic for filling cracks, gaps, and joints prior to application.
How Long Does Ultraflex Last?
When correctly installed with Ultraflex Matting and finished with the Ultratop topcoat, the Ultraflex system is BBA and ETE certified for a service life in excess of 25 years. Formal guarantees are available for 15, 20, or 25 years depending on the project specification.
The system's durability is underpinned by its seamless monolithic structure, long-term UV resistance provided by the Ultratop finish coat, BRoof(T4) fire classification, and thermal stability tested down to -35°C. The product is manufactured under ISO 14001 environmental management standards and is regularly audited by the BBA to confirm continued compliance.
How Is Ultraflex Applied?
Ultraflex uses a wet-on-wet application method, which is efficient, straightforward, and produces a consistently reinforced result.
- Confirm ambient and substrate temperature is between 2°C and 30°C. At the lower end, temperature must be rising, not falling.
- Ensure the substrate is clean, dry, and structurally sound. Fix all edge trims before application begins.
- Seal any cracks or gaps with Ultraflex Sealant - do not use silicone.
- Open the drum and stir thoroughly before use. If the product has been left to stand on site, stir again before applying.
- Apply Ultraflex generously using a solvent-resistant roller -start at perimeters and upstands (minimum 150mm height), then work into the field area.
- Dry-roll Ultraflex Matting into the wet liquid until the membrane is drawn through, then immediately apply a second coat of Ultraflex over the top to fully encapsulate the matting. Check carefully for pinholes or dry areas.
- Once the membrane is fully cured, apply a coat of Ultratop topcoat within 48 hours.
Coverage is typically 8-10m² per 15kg drum at a minimum application rate of 1.5kg/m², though this will vary with substrate porosity and surface condition. Working in manageable sections of approximately 1-2m² at a time keeps the wet-on-wet process controlled and ensures the matting is always laid into live, wet liquid.
OSB cold roof note: Ensure sufficient ventilation within the roof structure to prevent moisture and condensation damaging the support. If uncertain about ventilation, install a metal-lined self-adhesive VCL directly onto the support before applying Ultraflex.
Drying time is approximately 2-8 hours to touch dry, with the membrane fully trafficable within 24 hours.
What Is the Ultratop Topcoat and Is It Always Required?
Yes, Ultratop is a required part of the complete system. Ultraflex PU is an aromatic polyurethane, meaning it is not designed for direct long-term UV exposure without a protective topcoat applied over it.
Ultratop is a single-component aliphatic polyurethane resin providing a glossy, flexible, UV-resistant finish with good resistance to abrasion and weathering. It is suitable for roofs and areas with light pedestrian traffic. Coverage is approximately 30m² per drum at 150g/m² per coat, and it is tack-free in around 25 minutes at 23°C.
Ultratop WR is the preferred topcoat for more demanding applications — car parks, swimming pools, balconies with heavy footfall. This two-component high-resistance glossy polyurethane also resists algae and moss growth and is available in over ten colours.
Clearcoat is a single-component transparent aliphatic polyurethane used where preserving the original appearance of the surface is the priority. It is UV-resistant and fully trafficable once cured.
Whichever topcoat is used, it must be applied once the Ultraflex membrane is fully cured and no later than 48 hours after the Ultraflex application.
What Are the Key Technical Properties of Ultraflex?
| Property | Value |
|---|---|
| Specific gravity | 1,320–1,420 kg/m³ |
| Viscosity at 23°C | 2,650 cps |
| Dry extract | >90% |
| Flash point | 42°C |
| Shore A hardness (unreinforced) | >75 |
| Tensile strength (reinforced) | >10 MPa |
| Tensile strength (unreinforced) | >3 MPa |
| Elongation (unreinforced) | >400% |
| Elongation (reinforced) | >100 MPa |
| Concrete adherence | >2 MPa |
| Water vapour resistance | μ = 2,500 |
| Dry time | 2–8 hours (touch dry) |
| Fully trafficable | 24 hours |
| Application temperature | 2°C to 30°C |
| Tested temperature range | -35°C to +90°C |
What Certifications Does Ultraflex Hold?
Ultraflex holds one of the more comprehensive certification portfolios of any liquid membrane system on the UK market. The product is manufactured in the company's own factory and regularly audited by the BBA to confirm ongoing compliance.
- BBA (British Board of Agrément) — certified for a service life in excess of 25 years
- ETE (European Technical Approval)
- CE marking
- WRAS — approved for use with potable water (Ultraflex PW variant), tested to BS-6920
- BRoof(T4) — the highest fire classification available under UK regulations for external roofing
- NHBC approval
- Green Roof approval
- ISO 14001 — environmental management standard
- CFC and HCFC free
How Much Does Ultraflex Cost and How Much Do You Need?
Coverage will vary depending on substrate type and condition, but as a general planning guide:
| Product | Pack | Coverage |
|---|---|---|
| Ultraflex PU liquid membrane | 15kg drum | 8–10m² per drum (min. 1.5kg/m²) |
| Ultraflex PU — car park system | 15kg drum | ~7m² per drum (min. 2kg/m²) |
| Ultratop topcoat | Per drum | ~30m² at 150g/m² per coat |
| Quickcure accelerator | 1 tin per drum | One full tin per 15kg drum |
| Tixal thickener | 1 litre tin | 300–500ml per 15kg drum |
| Ultraprime Pro primer | 2-component | 150–200g/m² |
What Project Types Is Ultraflex Suitable For?
Ultraflex is a genuinely versatile system with published specifications for a wide range of project types, from standard domestic flat roofs through to demanding industrial and structural waterproofing applications.
- Flat roofs - both new-build (OSB cold roof and warm roof build-ups) and refurbishment overlay of felt, bitumen, single ply, GRP, asphalt, and other existing membranes
- Warm roofs -applied over PIR insulation with a carrier membrane
- Green and inverted roofs -compatible with geotextile and drainage layer build-ups; NHBC and Green Roof approved
- Corrugated and pitched sheet roofs - including asbestos cement sheet overlay using Tixal additive for pitched surfaces
- Balconies and terraces - fast return to use with Quickcure; Ultratop WR available in over ten colours
- Car parks - heavy wheel traffic-rated system with anti-skid aggregate finish
- Gutters and channels
Ready to order Ultraflex for your next project? You can buy Ultraflex PU liquid waterproofing here at All Flat Roofing Supplies.
