Sika SikaProof-312 HDPE SG IN
A pre-applied HDPE membrane that fuses to freshly poured concrete, sealing blindside basements and buried structures against groundwater with no path for lateral tracking.
What is it?
A pre-applied, fully bonded sheet membrane built from a virgin HDPE film, a high-bond adhesive layer and a weatherproof sand coating, made for below-ground waterproofing of reinforced concrete.
Where is it used?
Blindside and buried RCC works: basement rafts, retaining and single-sided formwork walls, footings, grade slabs, tunnels, subways and prefabricated foundations.
Why use it?
It bonds permanently to the concrete face poured against it, so even if the membrane is later breached, water cannot travel laterally to find an unsealed entry point.
How is it applied?
Loose-laid over blinding or fixed to formwork, sand side down, before reinforcement. Reinforcement is placed directly on top and concrete is cast within 45 days to activate the bond.
About Sika SikaProof-312 HDPE SG IN
SikaProof-312 HDPE SG IN belongs to the pre-applied family of waterproofing membranes, the type you fix in place before the structure exists rather than after. The sheet is built in three working layers: a virgin high-density polyethylene film that forms the watertight barrier, a pressure-sensitive adhesive that grips the concrete cast against it, and a granular sand coating that shields the adhesive from weather and foot traffic on site. Once concrete is poured onto the membrane, the adhesive keys into the fresh paste and cures into a continuous, intimate bond with the slab or wall face. It is declared as a bonded sheet membrane to IS 16471:2017, so it sits squarely within the Indian standard framework that specifiers and third-party checkers work to.
The reason this matters on real projects is access. Blindside basements, cut-and-cover tunnels, lift pits and single-sided shuttered walls give you no way to reach the outside face once construction moves on, so a post-applied coating is simply not an option there. SikaProof-312 solves that by going in first and then locking to the structure permanently. Because the bond is continuous, there is no drainage gap between membrane and concrete for water to travel through, which is the failure mode that lets loose-laid systems leak far from the point of damage. For contractors it is also a fast, cold-applied system: no torches, no primers on the sheet itself, and reinforcement laid straight over the top without a protective screed.
The technical insight
The whole system stands or falls on one idea: a mechanical and adhesive bond that is intimate enough to eliminate lateral water migration. When wet concrete is placed on the sand-and-adhesive face, cement paste works into the granular surface and the adhesive develops a grip that measures 1500 plus or minus 100 N/m in peel after seven days on concrete (ASTM D903 mod). That bond is not instant at full strength, and it is honest to say so: peel adhesion actually eases back before stabilising, settling near 1000 N/m around 21 days after casting. What you get in return is a membrane that behaves as if it were part of the concrete skin. If the sheet is ever punctured during backfill or service, water reaching the breach has nowhere to run because it cannot spread between the film and the slab. The HDPE film itself carries the barrier duty, tested to withstand more than 71 m of hydrostatic head (ASTM D5385 mod), while the greater than 25 MPa film tensile strength and 500 percent elongation (ASTM D412 mod) let it stretch over settlement and minor crack movement without splitting. Static puncture resistance of 1000 N (ASTM E154) covers the reality of rebar chairs and site loading before the pour.
Where it is used
- Basement raft slabs and podium foundations cast against blinding concrete
- Blindside retaining walls and single-sided (single-faced) formwork walls where the outer face is inaccessible
- Cut-and-cover tunnels, subways and underpass structures
- Lift pits, ramps and grade slabs in below-ground plant rooms
- Footings, pile caps and grade beams needing continuous under-slab protection
- Water-retaining and buried RCC structures exposed to aggressive groundwater and soils
- Extension and reconstruction works tying new below-ground concrete into existing structures
- Prefabricated and modular foundation elements requiring a factory-first waterproofing wrap
Key advantages
- Pre-applied and fully bonded, so it protects structures with no external access after casting
- Continuous intimate bond to concrete blocks lateral water tracking, containing any breach at its source
- Cold-applied and torch-free installation with fully adhered joints, safer and faster on congested sites
- Reinforcement is laid directly on the sheet with no protective screed, saving a full trade and cost line
- Virgin HDPE film rated beyond 71 m hydrostatic head suits deep water tables and high-pressure conditions
- High film elongation of around 500 percent bridges shrinkage cracks and accommodates settlement
- Weatherproof sand layer gives temporary UV and weather tolerance during the build programme
- Declared to IS 16471:2017, easing approval with consultants and third-party quality auditors
Limitations & considerations
- Not permanently UV-stable; it must be covered by concrete and cannot stay exposed as a final surface
- Concrete must be cast within 45 days of installation or bond performance is compromised
- The adhesive bond needs proper concrete mix design and workmanship to reach full grip; poor casting weakens it
- On double-faced formwork the manufacturer prefers post-applied systems, as some debonding can occur there
- Substrate must be smooth, stable and free of standing water, and gaps of 12 to 15 mm or more need filling first
- Application is limited to ambient and substrate temperatures between +5 C and +40 C
Selection & best practice
Prepare a firm, smooth substrate first: blinding, formwork or rigid insulation, with no standing water and large voids of 12 to 15 mm or more pre-filled. Loose-lay the membrane sand-side down on horizontal and inclined surfaces, or mechanically fix it to vertical formwork, keeping the HDPE film facing the concrete to be cast. Overlap side laps 80 to 100 mm and remove the release liner along the selvage; for transverse joints, scrape off the sand layer with a hot air gun and seal the lap with SikaProof cold-applied tape. Roll every joint firmly to drive out air pockets, and in cold or damp weather warm the tape and selvedge adhesive with a hot air gun to lift condensation and improve initial grip. Lay reinforcement directly over the sheet, protect it from puncture during steel fixing, and cast concrete within 45 days. Always work to the current SikaProof-312 Method Statement adjusted to site conditions.
Specifications
| Product type | Pre-applied, fully bonded HDPE self-adhesive sheet membrane with sand coating |
| Product declaration | Bonded sheet membrane to IS 16471:2017 |
| Effective thickness | HDPE film > 0.9 mm; composite membrane >= 1.5 mm |
| Tensile strength | >= 25 MPa (film), ASTM D412 mod |
| Elongation | 500 +/- 25 % (film), ASTM D412 mod |
| Water tightness | > 71 m of hydrostatic head, ASTM D5385 mod |
| Static puncture resistance | 1000 +/- 100 N, ASTM E154 |
| Adhesion in peel to concrete | 1500 +/- 100 N/m after 7 days (approx. 1000 N/m at 21 days), ASTM D903 mod |
| Roll size | 20 m long x 1.2 / 1.5 / 2.0 m wide; 100 mm selvage; laps 80-100 mm |
Industry use cases
High-rise & commercial basements
Deep multi-level car parks and podium rafts cast against secant piles or blinding, where the outer wall face is permanently buried and only a pre-applied bonded membrane can be inspected before backfill.
Metro & infrastructure
Cut-and-cover tunnel boxes, subway stations and underpasses that face sustained hydrostatic head and demand a membrane bonded continuously to the structural concrete.
Water & effluent structures
Buried tanks, sumps and treatment chambers in aggressive groundwater, where lateral water migration behind a coating would otherwise be impossible to trace or repair.
Industrial & plant foundations
Machine pits, cable trenches and grade slabs in factories and power projects needing a puncture-tolerant barrier that reinforcement can sit on directly.
Repair & extension works
Tying new below-ground concrete into existing basements or foundations, using a cold-applied system that installs safely alongside live site activity.
Frequently asked questions
What makes a pre-applied membrane like SikaProof-312 different from a normal waterproofing coating?
Why does the bond stopping lateral water migration matter so much?
How deep a water table can it handle?
How soon do we have to cast concrete after laying the membrane?
Can reinforcement be placed straight onto the sheet?
What sizes and accessories does it come in, and what else do we need?
How we position Sika SikaProof-312 HDPE SG IN
SikaProof-312 HDPE SG IN is the workhorse pre-applied membrane for blindside below-ground concrete. Within the Sika family, step up to SikaProof-312 HDPE SG W IN when you need heat-weldable selvedges for even more robust joints, and pair either with SikaProof Sandwich Tape-100 IN and the SikaProof detailing accessories for a complete watertight system; on the same projects, SikaSwell profiles and Sika waterbars handle construction and movement joints, while Sikadur and Sika MonoTop products cover any concrete repair before membrane laying. Where a client’s approved vendor list or basement design leans elsewhere, we also supply directly comparable pre-applied systems from Fosroc and post-applied crystalline and coating options where those suit better; talk to our technical desk and we will match the membrane to the substrate, the water head and the specification.
Fosroc Proofex Engage — Specify the Fosroc option when the project’s approved vendor list or basement design standard calls for a cell-mesh mechanically-keyed pre-applied membrane rather than a sand-coated adhesive-bonded one.
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