About Fosroc Proofex OFB

Fosroc Proofex OFB is a fleece-backed, fully bonded synthetic waterproofing membrane built on TPO/FPA chemistry. The sheet is produced by extruding granules made by blending ethylene-propylene rubber into a polypropylene matrix with stabilising additives, which yields a flexible, thermoplastic polyolefin alloy that has none of the plasticisers used in PVC membranes and gives off no VOCs. To the underside Fosroc laminates a synthetic polyester fleece, and both long edges carry a fleece-free selvedge so that adjacent rolls can be hot-air welded sheet-to-sheet. The membrane is deliberately two-toned, grey on the weathering face and a dark colour underneath, so that any cut, scuff or puncture made during installation shows up immediately against the contrasting layer.

The “OFB” in the name reflects the way it works on site: it is an Overlay, Fleece-Backed, fully bonded system. Rather than loose-laying or mechanically fixing the sheet, the applicator coats the substrate with Fosroc Proofex OFB Adhesive and rolls the fleece face into the adhesive while it is still wet. The fleece grips the adhesive and the substrate, producing a continuous bond across the whole deck. The practical benefit of a fully bonded membrane is that if the sheet is ever breached, water cannot migrate laterally between membrane and substrate to find a distant entry point, which makes leaks far easier to trace and repair, an important advantage on occupied podiums and planted roofs where the membrane is later buried under growing medium, screed or paving.

For an Indian project team, Proofex OFB sits in Fosroc’s premium roofing-membrane range and is positioned for the applications that punish liquid-applied coatings, namely landscaped podiums, terrace gardens, blue-green roofs and exposed flat roofs that must remain watertight for decades. Because it is a factory-made sheet of controlled thickness, it removes the wet-film-thickness uncertainty that dogs site-applied systems, and because the seams are heat-welded rather than glued, the joints become a homogeneous extension of the sheet itself. The product is installed by Fosroc-approved applicators, and Space Arc Engineering, as an authorised Fosroc distributor and applicator for Delhi NCR and Pan-India, supplies the membrane together with its full ancillary kit, the OFB Adhesive, jointing strips, TPO corners, metal termination strips, pipe collars and roof-drain outlets.

The technical insight

Proofex OFB is a TPO/FPA membrane, not a PVC one, and that distinction drives its specification. Polypropylene-alloy chemistry means there are no migrating plasticisers to leach out and embrittle the sheet over time, which is the headline reason TPO membranes carry long design lives. Fosroc’s data shows the sheet survives 2,500 hours of UV exposure with no cracking (EN 1297) and passes FLL / PD CEN/TS 14416 root-penetration testing, the two properties that matter most for exposed and green roofs respectively. The fleece backing is the second technical lever: it converts the smooth TPO sheet into a substrate-bondable membrane via the moisture-curing polyurethane OFB Adhesive, and the fully bonded result resists wind uplift without mechanical fasteners that would otherwise penetrate the waterproofing. The seam is the third: hot-air welding fuses the selvedge overlaps into a continuous weld of at least 50 mm, tested to break outside the joint (lap-joint strength to EN 12317/UEAtc), so the weld is stronger than the parent sheet. Mechanically the membrane is robust, with longitudinal/transverse elongation above 700-800% and dynamic puncture resistance well into the EN 12691 range, giving it the toughness to take foot traffic during landscaping and the cyclic movement of a concrete deck. The membrane is also non-flammable and, in the potable-water-suitable grade, passes BS 6920, broadening its use to water-retaining structures.

Where it is used

• Fully bonded waterproofing to podium decks and plaza decks over occupied/basement spaces
• Green roofs, garden roofs and intensive/extensive planted roofs requiring root resistance
• Exposed flat and low-slope concrete roofs needing long-term UV and weathering durability
• Sloping and curved roof waterproofing where a flexible welded sheet outperforms rigid systems
• Civil-engineering structures and buried decks where leak-tracing reliability is critical
• Terrace gardens and blue-green roofs on residential and commercial buildings
• Roofs subsequently overlaid with screed, paving, ballast or growing medium

Key advantages

• TPO/FPA chemistry: no plasticisers and no VOCs, so the sheet stays flexible and does not embrittle with age
• Fully bonded via fleece backing, leaks cannot track laterally under the sheet, making detection and repair simple
• Hot-air welded seams form a homogeneous joint that tests stronger than the parent membrane
• Verified root resistance (FLL / PD CEN/TS 14416), suitable for green and garden roofs without a separate root barrier
• High UV and weathering durability, 2,500 hrs UV with no cracking, supporting a 30-year-plus design life
• Factory-controlled thickness (1.2 mm / 1.5 mm) removes the wet-film-thickness variability of liquid coatings
• Two-tone grey/dark construction makes installation damage instantly visible for quick rectification
• Non-flammable sheet; potable-water-suitable grade passes BS 6920
• Backed by Fosroc-approved applicator network and a complete ancillary system (adhesive, corners, drains, metal strips)

Limitations & considerations

• Must be installed by trained, Fosroc-approved applicators using hot-air welding equipment, not a DIY or unskilled-labour system
• Requires a sound, even substrate free of cavities, projecting nibs, running water, curing compounds and contaminants
• Each roll weighs approximately 85 kg, so mechanical handling and careful manual lifting are needed on site
• TPO and PVC membranes are chemically incompatible, do not lap or weld OFB to existing PVC sheets
• Relies on the matching Proofex OFB Adhesive and correct open time (typically 5-10 min); over- or under-curing affects bond
• Prior adhesion testing is recommended on metal substrates before full application
• Primarily an above-ground / overlay system, it is not a substitute for a pre-applied membrane below a structural raft
• Store below 30 degrees C, horizontally, no more than one pallet high, weld quality drops if rolls are damaged or cold

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Proofex OFB

Fosroc Proofex OFB is Fosroc’s fleece-backed, fully bonded TPO sheet within the Proofex roofing range, and it is best understood as the premium, factory-controlled alternative to liquid-applied terrace and podium waterproofing. On the same project it commonly works alongside other Fosroc systems: its own Proofex OFB Adhesive and the Proofex OGP/ORG jointing strips, TPO corners, metal strips and drain outlets form the complete kit, while for below-structure or basement waterproofing teams often turn to Fosroc’s pre-applied Proofex Engage, and for liquid-applied detailing or smaller terraces to Fosroc’s Brushbond and Nitoproof ranges. Against the wider Indian market, the closest competitors to OFB are other TPO/FPA single-ply systems such as Sika Sarnafil TS and the membrane ranges from MBCC/Master Builders Solutions (formerly MBS) and STP Limited, while in the broader waterproofing conversation owners may also weigh liquid-applied options like Dr. Fixit’s polyurethane and acrylic systems for terraces. Where OFB stands out is the combination of a fully bonded fleece backing, hot-air welded seams, verified root resistance and the backing of a Fosroc-approved applicator network, which together make it a strong specification for landscaped podiums, green roofs and exposed flat roofs that must perform for 30 years or more. Space Arc Engineering can advise on whether OFB or an alternative Fosroc system best fits a given deck and detailing.

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