About Fosroc Membrane HDPE S2

Fosroc Membrane HDPE-S2 belongs to Fosroc’s HDPE pre-applied waterproofing family, sitting alongside the post-applied Fosroc Membrane HDPE-S and the structural HDPE-P membrane. Where conventional self-adhesive sheets bond to only one surface, HDPE-S2 is engineered as a dual-side self-adhesive underlay: a tough HDPE carrier film is coated with a pressure-sensitive adhesive on both faces. This is the detail that matters for below-ground work in India, where the dominant failure mode is not the membrane itself splitting but water migrating laterally in the gap between an unbonded membrane and the concrete. By bonding intimately to the poured concrete above and to the secondary membrane (or substrate) below, HDPE-S2 closes that gap and confines any breach to its immediate point of damage.

In a typical Space Arc-specified basement build, HDPE-S2 is the layer laid first on the blinding/mud-mat (or fixed against a confined retaining wall where there is no room for back-shuttering). The structural raft is then cast directly against it, so the fresh concrete keys into the adhesive face. On vertical confined walls it is paired with Fosroc Membrane HDPE-P as the outer, more robust layer, with the upper release film peeled only when the HDPE-P is offered up. The result is a continuous, two-membrane sandwich that behaves as a single bonded system rather than a loose-laid sheet sitting in a water channel.

The membrane is chemically inert, so it does not react with ponded waste, ground salts, sulphates, chlorides or hydrocarbons left in backfill – a real consideration on redeveloped industrial plots and reclaimed land around Delhi NCR, Mumbai and the southern metros. It is also compatible with the full Fosroc range of hydrophilic and PVC waterstops, so construction joints, kickers and pipe penetrations can be detailed within one manufacturer’s system rather than mixing incompatible trades. For Indian projects the relevant benchmark is IS 16471:2017, the code for pre-applied HDPE membranes, against which HDPE-S2 is positioned to deliver basement protection Grades 1, 2 and 3.

The technical insight

The performance of HDPE-S2 rests on three numbers that distributors and waterproofing applicators should hold in their heads. First, the HDPE carrier is thin (bare film around 0.5 mm, total membrane around 0.8 mm) but high in elongation – over 500 percent to ASTM D412 – which lets it bridge shrinkage cracking and minor settlement movement in the raft without tearing. Second, puncture resistance above ~600 N (ASTM E154) is what survives steel-fixing, foot traffic and aggregate during the cast; on Indian sites the membrane is almost always damaged during the works, not in service, so puncture and the matching 100 mm sealed-tape repair detail are the real-world safeguards. Third, the dual-side peel adhesion (around 880 N/m, ASTM D903 modified) and a hydrostatic head resistance exceeding 60 m mean the bonded sandwich resists the standing water pressure of a deep basement below the local water table. The key conceptual point: HDPE-S2 is a system component, not a standalone membrane. Its job is to anchor the waterproofing to the concrete on both faces so that water cannot run between membrane and structure – which is exactly why it is specified as an underlay beneath HDPE-P rather than as a single-layer solution.

Where it is used

• Pre-applied underlay beneath structural raft slabs cast on blinding, before the secondary Fosroc Membrane HDPE-P layer
• Below-ground waterproofing of basement boxes to IS 16471:2017 Grades 1, 2 and 3
• Confined retaining walls and zero-clearance perimeter walls where back-shuttering space is unavailable
• Podium decks and transfer slabs requiring a fully bonded tanking system
• Water-retaining and water-excluding structures such as tanks, lift pits and sumps
• Sites with contaminated ground – hydrocarbons, ground salts, sulphates and chlorides in backfill
• Multi-layer membrane systems where lateral water tracking must be eliminated by full bonding

Key advantages

• Dual-side self-adhesive bond to both the concrete and the secondary membrane eliminates the water channel that causes most below-ground leaks
• Fully bonded to poured concrete, so any damage stays localised and cannot track water across the structure
• High elongation (>500% to ASTM D412) accommodates shrinkage and minor structural movement
• Chemically inert – resists hydrocarbons, salts and chemicals in contaminated Indian infill sites
• Pre-applied, so it is installed before casting and needs no working space behind a confined wall
• No separate primer or external protection layer required for the membrane itself
• Compatible with the full Fosroc hydrophilic and PVC waterstop range for single-source detailing
• Positioned to deliver IS 16471:2017 basement Grades 1, 2 and 3 within one bonded system

Limitations & considerations

• It is an underlay, not a complete solution – it is intended to work with Fosroc Membrane HDPE-P, not as a single-layer membrane
• Thin carrier film (~0.8 mm total) is vulnerable to puncture during reinforcement fixing and concrete placement; the 100 mm sealed tape repair detail must be on site
• Demands a clean, dry, defect-free substrate (moisture content typically below 5% on vertical applications) and repair of honeycombing, cracks and tie-rod holes before installation
• Correct laps are critical – 75 mm side and 100 mm end overlaps must be rolled down and the top release film peeled at the right stage; poor workmanship defeats the bonded principle
• Backfill must be free of sharp objects and stones larger than ~50 mm or the membrane can be punctured after casting
• Pre-applied to confined walls means installation sequence cannot be reworked easily once concrete is cast against it
• Always confirm the latest India TDS values and grade claims with Fosroc, as specifications and roll sizes are revised periodically

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Membrane HDPE S2

Within the Fosroc range, HDPE-S2 is the pre-applied underlay that partners with Fosroc Membrane HDPE-P (the structural outer membrane) and complements the post-applied Fosroc Membrane HDPE-S used on cured vertical walls; construction joints are sealed with Fosroc hydrophilic and PVC waterstops and the 100 mm Fosroc Membrane HDPE Sealed Tape. Compared with pre-applied HDPE systems from other manufacturers – such as Sika Sikaproof and SikaBit pre-applied membranes, BASF/Master Builders Solutions (MBS) MasterSeal, Dr. Fixit pre-applied HDPE membranes and STP (Shalimar Tar Products) Cosmofin/HDPE ranges – HDPE-S2’s differentiator is its dual-side self-adhesive bonding and integration into a single-source Fosroc tanking system. For lower-risk or smaller residential basements, a single robust pre-applied membrane (HDPE-P alone) or a crystalline/cementitious approach may be more economical; HDPE-S2 earns its place on deep, high-water-table or contaminated-ground projects where eliminating lateral water tracking is the priority. Space Arc Engineering positions it honestly as a system component for demanding below-ground work, supplied with the matching HDPE-P, waterstops and tapes rather than as a one-product fix.

Related Waterproofing products

View all Waterproofing products →