Fosroc Proofex LM 1K Poly
Single-component, spray- or hand-applied polymer-modified bituminous liquid membrane for seamless external waterproofing of basements, retaining walls and buried structures.
What is it?
A one-component (1K), polymer-modified bituminous liquid-applied waterproofing membrane that cures to a seamless, flexible, crack-bridging film — part of Fosroc’s Proofex below-grade waterproofing system.
Where is it used?
External (positive-side) waterproofing of basements, retaining walls, foundations, lift pits, water tanks and buried RCC structures, plus intricate details like pipe penetrations and covings; it can also serve as a radon barrier.
Why use it?
It forms a jointless, fully-bonded membrane that bridges shrinkage cracks, can be applied to damp substrates, resists aggressive ground water and hydrostatic head up to 30 m, and goes down fast by airless spray or trowel/brush.
How is it applied?
Surface preparation and priming, then application in coats by airless spray, trowel or brush to a uniform wet-film build, optionally reinforced at details and movement zones, left to cure before protection and backfill.
About Fosroc Proofex LM 1K Poly
Fosroc Proofex LM 1K Poly is a single-component, polymer-modified bituminous (poly-bitumen) liquid membrane engineered for the external waterproofing of below-ground concrete and masonry. It sits within Fosroc’s well-established Proofex family of below-grade systems, and the “1K” designation marks it as the ready-to-use, one-component sibling of the classic two-component Proofex LM — there is no separate powder to gauge and batch-mix on site, which removes a common source of mixing error and speeds up application. Once applied, the wet emulsion coalesces and cures into a continuous, rubber-like elastomeric film that is fully bonded to the substrate. Because it is monolithic and seamless, it has no laps, joints or welds — the failure points that plague sheet-membrane and torch-applied systems at corners, pipe entries and re-entrant details. For Indian basements, water tanks, lift pits and foundation rafts that have to perform under a fluctuating water table, that jointless behaviour is the core value: water cannot track laterally between a bonded liquid membrane and the concrete the way it can behind a debonded sheet. The membrane is flexible and crack-bridging, so it accommodates the minor shrinkage and thermal movement that every green RCC structure goes through in the first years of its life. It tolerates damp (though not running-wet) substrates, which is a real advantage on Indian sites where concrete is rarely bone-dry and monsoon timelines are tight. It is also resistant to the aggressive sulphate- and chloride-laden ground water common to many Indian soils, and Fosroc lists it as suitable for use as a radon barrier — relevant for occupied basements and parking levels. It can be applied by airless spray for large rafts and walls, or by trowel and brush for detailing, and it is designed to integrate with the wider Proofex waterproofing system including protection boards and accessories.
The technical insight
The decisive technical distinction is “1K” (one-component) versus the two-component Proofex LM. The 2K version is a bitumen-rubber emulsion gauged on site with a hydraulically-setting filler powder, which lets it build a thick ~3.3 mm film in fewer passes and resist a higher head (Fosroc rates the 2K at up to 70 m), but it demands accurate mixing and a controlled pot life. The 1K Poly trades that very high head capacity (rated up to 30 m) for application simplicity: no batching, no pot-life clock, consistent material straight from the pack. For the overwhelming majority of Indian residential and commercial basements — typically one to three levels below grade with a head well under 30 m — the 1K envelope is more than adequate, and the reduced on-site variability often produces a more reliable result than a powerful product mixed poorly. Being a water-based bituminous emulsion, it is solvent-free and low-odour, so it is workable in confined pits and enclosed basements where solvent fumes would be a hazard. The performance hinges on wet-film control and cure: the coating must be built to the specified wet-film thickness in evenly-lapped coats, each coat allowed to cure (darken and lose tack) before the next, and the full system cured before it is protected and backfilled. Like all bituminous emulsions it is not designed for permanent UV exposure and must be covered. Because exact film-build, coverage and cure times are temperature- and version-dependent, the project-specific Fosroc India technical data sheet must govern the specification.
Where it is used
- External (positive-side) tanking of basement rafts, retaining walls and foundation walls before backfill
- Waterproofing of lift pits, sumps, machine pits and other buried RCC pits
- Below-ground water-retaining and water-excluding structures such as tanks and reservoirs
- Sealing of intricate details — pipe penetrations, covings, junctions and re-entrant corners
- Podium, plinth and buried-slab waterproofing within a protected build-up
- Radon barrier layer beneath occupied basements and parking levels
- Detailing and tie-in coat used alongside the wider Proofex waterproofing system
Key advantages
- Single-component and ready to use — no on-site gauging or powder mixing, reducing batching error
- Seamless and jointless — no laps, welds or overlaps that can fail at corners and penetrations
- Flexible with crack-bridging capability to accommodate shrinkage and thermal movement
- Can be applied to damp (not running-wet) substrates, suiting Indian site and monsoon conditions
- Fully bonded to the substrate, limiting lateral water tracking behind the membrane
- Resists hydrostatic head up to 30 m and resistant to aggressive ground water
- Applied fast by airless spray over large areas, or by trowel/brush for detailing
- Solvent-free, low-odour water-based emulsion — usable in confined basements and pits
- Can double as a radon barrier for occupied below-grade spaces
- Integrates with the Fosroc Proofex system of primers, protection boards and accessories
Limitations & considerations
- Rated to ~30 m hydrostatic head — for very deep or high-water-table structures the 2K Proofex LM (up to 70 m) or a sheet/HDPE system may be specified
- As a positive-side external membrane it must be applied before backfill; it is not a blindside or internal-tanking solution on its own
- Bituminous emulsion — not UV-stable; must be protected and covered, never left permanently exposed
- Requires correct surface preparation, priming and wet-film build per coat; under-application compromises performance
- Water-based cure is temperature- and humidity-dependent and slows in cold or very humid conditions
- Substrate may be damp but not running-wet, with no active water ingress during application and cure
- Needs protection (boards/screed) before and during backfilling to avoid mechanical damage
- Exact coverage, film thickness and cure times must be taken from the current Fosroc India TDS, not assumed
Selection & best practice
Specify Proofex LM 1K Poly only where the design hydrostatic head is within its ~30 m rating; for deeper structures step up to 2K Proofex LM or a sheet/HDPE system. Prepare the substrate to a sound, clean, laitance-free surface, fill blowholes and form coving fillets at all wall-to-floor junctions, and prime per the Fosroc system. Treat penetrations, construction joints and re-entrant corners as a separate detailing coat — often with reinforcement — before the main membrane. Apply in the specified number of coats to the full wet-film thickness, allowing each coat to cure before the next, and check build with a wet-film gauge rather than by eye. The substrate may be damp but must have no running water; do not apply over ponded surfaces or in active rain. Allow the system to fully cure, then install protection board or a protective screed before backfilling, and backfill carefully to avoid mechanical damage. Always work to the current Fosroc India product datasheet and method statement for the exact version supplied, and engage an authorised applicator (such as Space Arc) for warranty-grade installation.
Specifications
| Product type | Single-component (1K) polymer-modified bituminous liquid-applied waterproofing membrane |
| System | Liquid membrane for external below-grade waterproofing; part of the Fosroc Proofex system |
| Components | One-component, ready to use (no site mixing of separate powder) |
| Hydrostatic head resistance | Up to 30 metres (per Fosroc product page) |
| Film character | Seamless, flexible, crack-bridging once cured |
| Substrate condition | Can be applied to damp surfaces (no running/standing water) |
| Application method | Airless spray application or by hand (trowel/brush) |
| Chemical resistance | Resistant to aggressive ground water |
| Special function | Can be used as a radon barrier |
| Compatibility | Compatible with the Fosroc Proofex waterproofing system |
| UV / exposure | Not for permanent exposure; must be protected and covered before backfill |
| Coverage, film thickness, cure & pack size | Version- and temperature-dependent; refer to the current Fosroc India TDS (for comparison, 2K Proofex LM is ~4 kg/m² at ~3.3 mm) |
Industry use cases
Residential & commercial basements
Positive-side tanking of basement rafts and retaining walls in multi-level apartment and office projects across Delhi NCR before backfill, where a seamless membrane outperforms lapped sheets at corners and penetrations.
Infrastructure & buried structures
Waterproofing of lift pits, sumps, machine pits and buried RCC chambers in metro, hospital and institutional builds, including aggressive-ground-water locations.
Water-retaining structures
External waterproofing of buried tanks, reservoirs and treatment-plant structures within a protected build-up.
Healthcare & occupied basements
Used as a radon barrier and damp-proofing layer beneath occupied basements, parking levels and plant rooms.
Detailing & remediation
Hand-applied detailing coat at pipe entries, covings and junctions, tying into Proofex sheet or board systems on larger waterproofing packages.
Frequently asked questions
Is Proofex LM 1K Poly a one-component or two-component product?
How much hydrostatic head can it resist?
Can it be applied to damp concrete?
Where is it used, and is it suitable for interiors?
Can it act as a radon barrier?
How is it applied and does it need protection?
How we position Fosroc Proofex LM 1K Poly
Within the Fosroc range, Proofex LM 1K Poly is the simplified, one-component liquid membrane for everyday below-grade waterproofing where the head is within ~30 m. Its natural stablemate is the two-component Proofex LM, which builds a thicker film and resists up to 70 m head but needs careful site mixing — choose the 2K where depth or water table demands it, and the 1K Poly where consistency and speed matter more. For sheet-based tanking, Fosroc offers the Proofex Engage HDPE pre-applied (blindside) membrane and the Proofex Torchseal 3P/4P APP-modified bitumen membranes; for cementitious internal tanking, Fosroc Brushbond and the Renderoc/Nitobond accessories complete the system. Against competitors, credible alternatives a consultant might evaluate include Sika (Sikalastic / SikaProof liquid and pre-applied membranes), MBCC/Master Builders Solutions (MasterSeal liquid membranes), Pidilite Dr. Fixit (LW+, Newcoat and the Roofseal/Torchshield ranges) and STP Limited (Shalimar Tar Products — bituminous coatings and APP membranes). Dr. Fixit and STP are typically the value-positioned bituminous options, while Sika and Fosroc sit at the specification-grade, system-warranty end. As an authorised Fosroc distributor and applicator covering Delhi NCR and Pan-India, Space Arc Engineering supplies Proofex LM 1K Poly with the matching primers, protection boards and detailing products, and provides warranty-grade application — always governed by the current Fosroc India technical data sheet for the exact version supplied.
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