Dr. Fixit Prebond W
The pre-applied HDPE membrane that welds itself into the pour — stopping water tracking before it starts, on basements, metro boxes and tunnels across Delhi NCR.
What is it?
A pre-applied, fully-bonded HDPE waterproofing membrane whose pressure-sensitive adhesive layer locks permanently to the underside of concrete as it’s poured directly on top.
Where is it used?
Basement rafts, metro and subway station boxes, tunnels and underground caverns, blind-side retaining walls, and other below-grade structures where concrete is cast straight onto the waterproofing.
Why use it?
It removes the single biggest failure mode of loose-laid membranes — lateral water tracking. Because the membrane physically bonds to the concrete, a puncture stays a localised leak instead of spreading water metres away before it surfaces.
How is it applied?
Rolled out adhesive-side up over prepared blinding concrete or formwork, joints hot-wedge welded at 380-400°C with 100 mm overlaps, then reinforcement and structural concrete placed directly on top with no protective screed required.
About Dr. Fixit Prebond W
Dr. Fixit Prebond W is a pre-applied, fully-bonded HDPE membrane engineered to solve one specific, expensive problem: water finding its way sideways under a slab after a loose-laid membrane gets punctured. The system is built from an HDPE film laminated to a pressure-sensitive adhesive layer, itself protected by a release film until installation. Crews roll it out adhesive-side up over prepared blinding concrete or formwork, weld the joints edge to edge with a hot-wedge machine, then place reinforcement and pour structural concrete directly on top — no sand screed, no protection board. As the wet concrete cures against the membrane, the adhesive layer activates and locks permanently to the underside of the slab. That mechanical and chemical bond is the entire point: because there is no air gap or loose interface between membrane and concrete, water that finds a pinhole anywhere on the sheet cannot travel laterally to spread damage — it stays confined to that single point, which is a fundamentally different failure mode from the classic loose-laid membrane that lets water track for metres before it shows up as a stain somewhere else entirely.
Within Pidilite’s Dr. Fixit range this sits in the “large projects” technical portfolio alongside Prebond S, Prebond E and Prebond Pro — the family Space Arc Engineering specifies and applies across basement, metro and tunnel packages in Delhi NCR. Prebond W is the fully-bonded, pressure-sensitive variant meant for structures cast directly onto it; it is not a general-purpose roofing or podium membrane, and it is not a DIY product — hot-wedge welding at controlled temperature is non-negotiable for the joint integrity the system depends on. Space Arc supplies and applies Prebond W as part of full basement waterproofing packages, typically pairing it with Dr. Fixit’s crystalline or bentonite systems at construction joints and pile/diaphragm wall interfaces where a single membrane type cannot cover every geometry on site.
The technical insight
The number that actually differentiates Prebond W from a generic loose-laid HDPE sheet is the 1500 N/m peel adhesion to concrete combined with the 15,000 N/m lap-joint shear strength. Most below-grade membrane failures on real sites aren’t the membrane material tearing — they’re water finding one weak point (a pin-hole, a bad lap, a nail through the sheet during rebar fixing) and then travelling sideways underneath the slab through the air gap that a loose-laid or torch-applied membrane leaves behind, before resurfacing as a leak or damp patch metres from the actual damage. A fully-bonded, adhesive-activated membrane removes that air gap entirely: once the concrete cures against it, water arriving at a puncture point has nowhere to travel except straight up through that same hole, which is dramatically easier to trace and repair than chasing a leak across an entire basement raft. The 70 m hydrostatic head rating (ASTM D5385) and BS 8102:2022 Type A classification also matter for how a waterproofing consultant reads this on a drawing — Type A means the membrane itself is the water barrier, as distinct from Type B (structurally integral, e.g. waterproof concrete) or Type C (drained cavity) protection, and BS 8102 guidance generally still recommends combining Type A with some level of drainage or damp-management detailing on higher-consequence structures rather than treating any single barrier system as a complete solution on its own.
Where it is used
- Basement raft foundations and slabs, particularly on high water-table plots across Noida, Greater Noida, Gurugram and the Yamuna floodplain belt
- Subway and underground metro station box structures
- Tunnels, underground caverns and other confined underground civil works
- Blind-side waterproofing on retaining walls where excavation runs to the property line and there’s no working space behind the wall
- Below-grade water and sewage treatment structures, tanks and STP-adjacent civil works
- Multi-level underground parking podiums under high-rise and commercial developments
- Lift pits, sump pits and other localised depressions cast within a waterproofed raft
- Piled or diaphragm-wall basements where the membrane is welded to a rigid backing before rebar and concrete follow
Key advantages
- Fully-bonded adhesive layer prevents lateral water migration (“tracking”) between the membrane and the concrete — a puncture stays a point leak instead of flooding an entire bay
- Hot-wedge welded joints give a continuous, tested seal: single-weld overlaps of 50 mm minimum, or a double-weld with an air-channel test gap for on-site QA
- No protective screed needed — reinforcement is laid straight onto the membrane, which trims a construction step and a day or more off the basement-slab cycle
- 1000-1500 N puncture resistance (depending on 1.5 mm or 1.8 mm grade) tolerates rebar chairs, aggregate and site foot traffic better than thin loose-laid sheets
- Resists 70 m of hydrostatic head per ASTM D5385, which comfortably covers the water-table conditions seen on most NCR basement and metro-box excavations
- Chemically resistant to acid, alkali, chlorides and sulphate attack, with a manufacturer-cited 25-year durability test basis for long-design-life structures
- Large 2.0-2.4 m roll widths mean fewer joints per square metre than narrower membranes, which is where most on-site leak paths actually originate
- Meets IS 16471:2017 and BS 8102:2022 Type A protection criteria, so it drops straight into consultant specifications without a substitution debate
Limitations & considerations
- Requires a trained welding crew and hot-wedge equipment (Leister Twinny or equivalent, 380-400°C) — it is a specialist install, not something a general mason’s crew picks up on day one
- Primary design intent is horizontal (pour-onto) application; vertical/blind-side use needs termination bars, careful sequencing and welding completed before reinforcement goes in, which adds programme complexity
- UV/weather exposure is rated to 45 days — membrane left uncovered longer than that on a delayed pour needs manufacturer sign-off before concreting
- Substrate must be sound, level and free of gaps, cavities or sharp projections; poor blinding-concrete finish will compromise both the weld quality and the eventual adhesive bond
- As a Type A (barrier) protection system under BS 8102:2022, high-consequence basements (habitable, sensitive equipment) are still advised to combine it with drainage or damp-management detailing rather than relying on the membrane alone
- Manufacturer notes the adhesive can feel slightly tacky underfoot in hot weather before the pour — cosmetic and expected, but it means the exposed membrane needs site discipline (no loose grit dragged across it) until concrete goes down
Selection & best practice
Treat surface prep as the actual determinant of performance, not a formality: blinding concrete must be free of loose aggregate and sharp protrusions before rollout, and while it doesn’t need to be bone dry, standing water has to be removed first. Lay the membrane adhesive-side facing the concrete pour and HDPE film facing the substrate, stagger end laps so overlaps don’t stack up, and overlap successive sheets by a minimum 100 mm along the marked selvedge. Weld with a hot-wedge machine at 380-400°C running 3-4 rmt/min, keep single-weld overlaps at 50 mm minimum (or run the double-weld/air-channel detail so every joint can be air-lance tested before cover-up), and tape the overlap area with single-sided HDPE tape afterward. Clean sand and adhesive residue off the membrane surface before welding at any joint — contamination there is the most common cause of a failed weld on site. On the raft edges, extend the membrane up to 200 mm from the bottom of the PCC, and on vertical/blind-side runs, hang and secure the membrane top with a termination batten roughly 50 mm below the top edge, completing all vertical welding before reinforcement is fixed. Finally, sequence the pour so the membrane isn’t left exposed anywhere near its 45-day UV limit — cover or concrete over it as early as the programme allows.
Specifications
| System type / standard compliance | Pre-applied fully-bonded HDPE weldable membrane; complies with IS 16471:2017 and BS 8102:2022 Type A protection |
| Composite membrane thickness | 1.5 mm or 1.8 mm (bare HDPE film 0.9 mm / 1.2 mm) — ASTM D3767 |
| Tensile strength (bare HDPE) | 25 N/mm² (1.5 mm grade) / 28 N/mm² (1.8 mm grade) — ASTM D412 |
| Elongation at break | 500% (both grades) — ASTM D412 |
| Puncture resistance | 1000 N (1.5 mm) / 1500 N (1.8 mm) — ASTM E154 |
| Resistance to hydrostatic head | 70 m — ASTM D5385 |
| Peel adhesion to concrete / Lap joint shear strength | 1500 N/m peel adhesion — ASTM D903; 15,000 N/m lap-joint shear — ASTM D6392 |
| Low-temperature flexibility / UV resistance | Pass at -25°C (ASTM D1970); UV exposure rated to 45 days (internal test method) |
| Packaging & shelf life | Rolls 20 m x 2.4 m and 20 m x 2.0 m at 1.5 mm / 1.8 mm composite thickness; 12-month shelf life in covered, secured storage |
Industry use cases
Metro / mass-transit infrastructure
Underground metro station boxes and tunnel sections specified with IS 16471:2017 / BS 8102:2022 Type A protection, where long design life and hydrostatic-head resistance are contract requirements rather than nice-to-haves.
High water-table residential basements
Basement rafts on plots across Noida, Greater Noida and the Yamuna floodplain belt, where seasonal water-table rise makes a fully-bonded membrane preferable to loose-laid systems prone to tracking.
Constrained urban plots (blind-side)
Retaining walls cast against shoring or a pile/diaphragm wall with no working space behind, where the membrane is welded onto the rigid backing before reinforcement and structural concrete follow.
Water and wastewater structures
Underground tanks, sumps and STP-adjacent civil structures where sulphate and chloride resistance in the surrounding soil or effluent matters as much as the hydrostatic barrier itself.
Commercial basement parking podiums
Multi-level underground parking under commercial or high-rise developments, where the no-screed installation shortens the raft-slab construction cycle.
Frequently asked questions
Does Prebond W need a screed or protection board on top before I place reinforcement?
Can Prebond W be used on vertical walls, or only under the raft?
What’s the difference between the 1.5 mm and 1.8 mm grades?
Does the substrate need to be completely dry before we roll out the membrane?
What welding equipment do we need, and can our regular waterproofing crew do it?
How long can the membrane sit exposed on site before we pour concrete over it?
How we position Dr. Fixit Prebond W
Prebond W sits alongside Dr. Fixit Prebond S (a loose-laid, sand-faced HDPE membrane without the pressure-sensitive adhesive layer — chosen where a fully-bonded system isn’t feasible or budget is tighter), Prebond E (an economy-grade HDPE membrane) and Prebond Pro within Pidilite’s large-projects waterproofing portfolio, so a single Dr. Fixit specification can cover fully-bonded, loose-laid and premium grades from one manufacturer relationship. Outside the Dr. Fixit family, the closest genuine equivalent is Fosroc’s Proofex Engage, which achieves a similar pre-applied, cast-onto-membrane outcome through a mechanically-keyed cell-mesh surface rather than an adhesive bond — a real alternative for teams already standardised on Fosroc systems or those who prefer a mechanical-interlock mechanism over an adhesive one. Space Arc Engineering, as an authorised Dr. Fixit distributor and applicator, typically specifies Prebond W as the primary raft/basement membrane and pairs it with crystalline waterproofing or joint-specific systems (waterstops, injection grouts) at construction joints and penetrations that a sheet membrane alone can’t seal.
Fosroc Proofex Engage — A specifier who prefers a mechanically-keyed system (concrete locks into a cell-mesh surface rather than bonding to an adhesive layer) or is already standardised on Fosroc for the rest of the basement package might choose Proofex Engage over Prebond W, particularly for blind-side and tunnel-lining work.
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