STP ShaliHDPE SA
The pre-applied HDPE membrane that fuses into the concrete as it cures — sealing Delhi NCR basements against water, soil gas and lateral leak paths.
What is it?
A 1.2-1.5 mm white, self-adhesive HDPE sheet membrane built for the pre-applied (blindside) waterproofing method — laid before the structural concrete is poured, not stuck down after.
Where is it used?
Basement raft slabs, retaining walls cast against shuttering or lagging, lift pits, tunnels, podium decks and any buried RCC structure that can’t be waterproofed from the outside once construction is finished.
Why use it?
Its reactive adhesive/granule layer chemically bonds into the wet concrete as it hydrates, so if the membrane is later nicked, water can’t travel sideways underneath it looking for a crack — the failure mode that loose-laid or torch-on sheets are prone to.
How is it applied?
Rolled out adhesive-side-up (facing the coming concrete pour) over blinding concrete or shuttering, overlapped 75-80mm with the release liner peeled progressively and every joint rolled firm, before rebar fixing and the structural pour proceed.
About STP ShaliHDPE SA
ShaliHDPE SA is a self-adhesive HDPE waterproofing membrane from STP Limited, an Indian construction-chemicals manufacturer with over 85 years in the market, built specifically for the pre-applied (blindside) method — laid on blinding concrete or shuttering before the structural pour goes in, rather than stuck down afterwards. The sheet is a three-layer laminate: a cross-laminated high-density polyethylene carrier film for dimensional stability, a pressure-sensitive polymer adhesive, and a reactive inorganic granule coating under a peel-off release liner that’s designed to interlock with fresh concrete as it hydrates. That third layer is really the point of the product — it turns a mechanically fixed sheet into something closer to a monolithic seal.
For Delhi NCR basements — multi-level parking under high-rises, metro and utility tunnel sections, retaining walls poured against shoring where there’s no room to come back and work from outside later — that pre-pour bond matters more than headline thickness. Once concrete cures against ShaliHDPE SA, water finding a pinhole in the membrane can’t migrate sideways beneath it hunting for a crack in the slab; the bond compartmentalises any breach to its point of entry. It’s supplied in 1.2mm and 1.5mm gauges, in 1.2m and 2m wide rolls, giving specifiers a way to match membrane weight to hydrostatic pressure and expected site abuse without redesigning the waterproofing detail.
The technical insight
The figure worth reading twice on STP’s data sheet is the >900 N/m peel strength to post-cured concrete set against a >1215 N puncture resistance — the membrane is engineered to be harder to tear than to un-bond. Paired with 700-900% elongation (ASTM D412), it can stretch across minor differential settlement or hairline shrinkage cracking in the slab without the bond letting go, which is the actual failure mode pre-applied systems exist to prevent. The 60-73m hydrostatic head rating (ASTM D5385) and sub-0.30% water absorption (ASTM D570) are what matter for high water-table basements common across NCR’s river-plain geology, while -23°C low-temperature flexibility is more a transport and storage safeguard than a site-relevant number in North Indian conditions.
Where it is used
- Basement raft/mat slab waterproofing, laid on blinding concrete before the structural pour
- Retaining walls cast against shuttering, piling or lagging with no external access later
- Lift pits, sump pits and other below-water-table pockets within a basement
- Tunnel linings and underground utility or metro structures
- Podium decks and planted (green) roofs, installed beneath the growing medium
- Underground parking structures on sites with a high seasonal water table
- Structures on contaminated or ex-landfill sites needing a methane/soil-gas barrier
- Split-level, multi-basement high-rise foundations with tight pour sequencing
Key advantages
- Chemically cross-links with the concrete pour, so a punctured membrane doesn’t let water migrate sideways to find a crack elsewhere
- Fully cold, self-adhesive application — no torches or open flame near formwork, rebar cages or site labour
- Uniform 1.2mm/1.5mm gauge, unlike liquid-applied coatings that can thin out on verticals and corners
- >1215 N puncture resistance survives rebar-fixing traffic and site movement before the pour
- 700-900% elongation tolerates minor slab shrinkage and settlement without the bond failing
- 60-73m hydrostatic head rating suits NCR sites with a high or seasonally rising water table
- Doubles as a barrier to ground salts, chemicals and methane/soil gases, not just water
- Weather-resistant and trafficable once laid, so rebar fixing can proceed straight over it
Limitations & considerations
- It’s a pre-pour system that has to be planned and laid before concrete goes in — not a fix for a basement that’s already leaking
- Cannot be applied over uncured ‘green’ concrete or damp substrates; trapped vapour pressure can blister the sheet
- Application window is +5°C to +45°C substrate/ambient with RH under 75%, which needs sequencing around Delhi’s monsoon and peak-summer site conditions
- Overlap and rolling technique is the main site risk — under-lapped or poorly rolled joints are the most common cause of leaks in pre-applied systems generally
- Exposed membrane must be protected within 7 days; long gaps between laying and pouring invite mechanical damage from other trades
- Committing to a pre-applied detail early in design means late changes to basement footprint or level are more disruptive to rework than with a post-applied system
Selection & best practice
Treat the blinding concrete or shuttering face as a finished surface before the membrane goes down — grind off protrusions, fill blowholes and honeycombing, and blow off dust with dry air; ShaliHDPE SA is only as good as what it’s stuck to. Keep 75-80mm overlaps consistent, peel the release liner progressively rather than all at once, and roll every joint firm with a heavy roller rather than relying on adhesive tack alone. On vertical faces against shuttering, fix through the selvedge with a termination bar instead of trusting the adhesive to carry the sheet’s own weight. Sequence rebar fixing carefully once the membrane is down: it’s puncture-resistant, not puncture-proof, and any nick found before the pour should be patched immediately with STP’s compatible 80mm self-adhesive tape rather than left for the concrete to seal on its own.
Specifications
| Thickness | 1.2 mm and 1.5 mm (±1%) |
| Roll size | 1.2 m x 20 m and 2 m x 20 m |
| Tensile strength (ASTM D412) | 25-29 MPa |
| Elongation at break (ASTM D412) | 700-900% |
| Puncture resistance (ASTM E154) | >1215 N |
| Lap peel adhesion (ASTM D1000) | 1500-1600 N/m |
| Resistance to hydrostatic head (ASTM D5385) | 60-73 m |
| Water absorption (ASTM D570) | <0.30% |
| Shelf life | 12 months, stored as per manufacturer recommendations |
Industry use cases
High-rise residential/commercial basements, Delhi NCR
Blindside waterproofing of raft slabs and retaining walls in multi-level basement parking on high water-table sites.
Metro and underground infrastructure
Pre-applied lining for tunnel sections and underground utility structures where post-construction access isn’t possible.
Green/planted roofs and podium decks
HDPE barrier laid beneath growing medium on terrace gardens and podium landscaping.
Industrial basements on contaminated sites
Combined water and methane/soil-gas barrier for structures on ex-industrial or landfill-adjacent land.
Lift pits and sump waterproofing
Below-water-table pockets within a larger basement pour, detailed into the main membrane run.
Frequently asked questions
Can ShaliHDPE SA be installed on an existing basement that’s already leaking?
What’s the practical difference between the 1.2mm and 1.5mm gauge?
Does the substrate need a primer before laying the membrane?
How is this different from the torch-on bituminous membranes we’ve used before?
What happens if the membrane gets punctured on site before the concrete is poured?
How long can rolls sit on site before they’re laid?
How we position STP ShaliHDPE SA
Within STP’s own range, ShaliHDPE SA sits specifically at the pre-applied/blindside end of the waterproofing line-up — for above-grade work, retrofit, or where torch-on flexibility is preferred, STP’s post-applied membrane and cementitious/crystalline systems are the better fit, and Space Arc’s applicator team can help match the system to the actual pour sequence rather than defaulting to one product. The closest genuine equivalent outside the STP range is Fosroc’s Proofex Engage, which uses the same pre-applied HDPE-with-reactive-adhesive principle and carries BS EN 13967 certification; a specifier already standardised on Fosroc documentation for other packages on a project, or one who needs that specific European standard referenced in a tender, may lean that way. For most Delhi NCR basement jobs where local stock, technical support and cost matter as much as the certificate, ShaliHDPE SA is the more practical call.
Fosroc Proofex Engage — Specifiers who need BS EN 13967-certified documentation or are already standardised on Fosroc’s Proofex range for other blocks of a project may prefer Proofex Engage, though ShaliHDPE SA delivers comparable pre-applied performance at a more competitive landed cost for Delhi NCR sites.
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