STP ShaliUrethane LHM Plus
A high-elongation, single-component polyurethane liquid membrane that cures with atmospheric moisture into a seamless, crack-bridging skin for exposed roofs, terraces and podium decks.
What is it?
A single-component, solvent-based, moisture-cured modified polyurethane elastomeric liquid membrane from STP, engineered as the higher-performance grade in the ShaliUrethane LHM family with elevated elongation and tensile strength.
Where is it used?
Exposed flat roofs, terraces, podium and balcony decks, terrace gardens and elevated walkways where a seamless, root-resistant, foot-durable waterproofing skin is required.
Why use it?
It cures into a joint-free monolithic membrane that bridges thermal and shrinkage cracks, resists ponding water and root growth, and bonds tightly to concrete without the mixing and pot-life constraints of two-part systems.
How is it applied?
Prime the prepared deck, then apply two brush, roller or airless-spray coats at roughly 800 g/m each (about 2 mm total), optionally reinforced with 45 GSM geotextile, and finish exposed areas with an aliphatic UV top coat.
About STP ShaliUrethane LHM Plus
STP ShaliUrethane LHM Plus is a liquid-applied polyurethane waterproofing membrane built for the parts of a building that take the harshest beating — the exposed roof slab, the podium deck, the open terrace. It arrives as a single ready-to-use component that needs no site mixing or metering. Once spread, it reacts with humidity in the air and cures into a continuous, rubber-like skin with no laps, seams or joints for water to exploit. That seamless quality is the whole point on a roof: the failure points of sheet systems are their overlaps and terminations, and a poured liquid membrane simply does away with them, wrapping drains, upstands and parapet junctions in one unbroken film.
Within STP’s ShaliUrethane range, LHM Plus sits above the standard LHM grade, offering higher elongation and tensile strength for decks that flex, move and cycle through Indian temperature extremes. It stays hydrophobic and elastic across a wide service band, recovers well after stretching over a moving crack, and resists the root penetration that plagues terrace gardens and green roofs. Because it is an aromatic polyurethane, its colour will shift under direct sun over time — a cosmetic change only — which is why Space Arc specifies an aliphatic UV top coat or a protective screed on every exposed installation so the membrane’s mechanical life is never compromised.
The technical insight
The membrane works on moisture-cure chemistry: the single-component resin carries reactive isocyanate groups that pull humidity from the air and cross-link into a dense, high-molecular-weight polyurethane network. That reaction is what turns a wet coat into a tough elastomer without any hardener being added on site — so there is no pot life to race against and no mix-ratio error to make. The cured film’s value lies in the balance it strikes: very high elongation lets it stretch across a crack that opens under thermal movement, while its elastic recovery pulls it back when the crack closes, so it keeps sealing through repeated day-night and seasonal cycles rather than tearing on the first big movement. High solids content means most of what you apply stays on the deck as membrane instead of flashing off, giving a reliable dry-film build per coat. The trade-off inherent to an aromatic PU is UV colour instability, so the system is deliberately designed as a base membrane plus a UV-stable finish — the aliphatic top coat takes the sunlight while the LHM Plus base does the waterproofing underneath.
Where it is used
- Exposed flat roofs and RCC terrace slabs in commercial and residential buildings
- Podium decks, balconies and sit-out areas over occupied space
- Terrace gardens and green-roof zones needing root-resistant waterproofing
- Elevated walkways and inspection platforms carrying light foot traffic
- Coastal and industrial roofs exposed to aggressive, humid atmospheres
- Wet areas and equipment decks where a seamless monolithic skin is preferred
- Refurbishment of ageing roofs where a liquid overlay avoids tear-off
- Detailing around drains, upstands, parapet grooves and pipe penetrations
Key advantages
- Single-component and ready to use — no on-site mixing, metering or pot-life pressure
- Cures into a fully seamless, monolithic membrane with no laps or joints to fail
- High elongation with strong elastic recovery for reliable crack bridging
- Root-resistant, making it suitable for terrace gardens and green roofs
- Excellent adhesion to concrete for a fully bonded system that resists lateral water tracking
- Conforms to ASTM C-836 and ASTM C-898 for liquid-applied elastomeric membranes
- Applies by brush, roller or airless spray to suit deck size and detailing
- Optional geotextile reinforcement lets the same product be tuned up for higher mechanical duty
Limitations & considerations
- Aromatic PU chemistry discolours under UV — always needs an aliphatic top coat or protective screed on exposed decks
- Not a stand-alone finished wearing surface; trafficable areas require a protection coat or screed
- Substrate must be sound, clean and with moisture content below about 5% before application
- Being solvent-based it is flammable and releases vapour — needs adequate ventilation and ignition control during application
- Moisture cure is humidity- and temperature-dependent, so cure times stretch in cold or very dry conditions
- Once a container is opened the material must be used within a few hours before skinning begins
Selection & best practice
Success is decided at the substrate. Grind or mechanically clean the deck to remove laitance, oil and loose matter, cut and fill cracks with a polymer-modified mortar, form 75 mm coving at all wall junctions, and confirm a fall of roughly 1:100 to drains so water never stands. Check that surface moisture is under about 5% before you start. Prime with the matched STP primer (ShaliPrime PUM or 2E LC) and apply the first LHM Plus coat while the primer is still tacky; where higher mechanical strength or detailing security is needed, embed 45 GSM geotextile into the wet coat. Build two coats at around 800 g/m each to roughly 2 mm total, terminate the membrane into a parapet groove about 200 mm up the wall, and let it cure fully — around 36 hours — before further work. Finish exposed areas with an aliphatic UV top coat (such as ShaliProtek 2AC PU TC) or, for foot traffic, a high-abrasion coat or geotextile-separated protection screed, and always run a ponding test after about seven days before handover.
Specifications
| Product type | Single-component, solvent-based, moisture-cured modified PU elastomeric liquid membrane |
| Standards | Conforms to ASTM C-836 and ASTM C-898 |
| Elongation (LHM Plus grade) | >600% (enhanced vs standard LHM) |
| Tensile strength (LHM Plus grade) | >4 MPa (enhanced vs standard LHM) |
| Hardness | Approx. 50 Shore A |
| Solids content | 90 +/- 2% by weight |
| VOC content | 115 +/- 5 g/kg |
| Coverage / consumption | 1.60-1.65 kg/m per mm; approx. 800 g/m per coat, 2 coats (~2 mm) |
| Application & pack | Brush / roller / airless spray; supplied in 25 kg drum; ~9 months shelf life |
Industry use cases
Commercial & IT parks
Large exposed roof slabs and equipment decks where a seamless, spray-applied membrane covers ground fast and eliminates the lap failures typical of sheet systems.
Premium residential
Podium decks, terraces and balconies over habitable space, finished with a UV top coat or tile-over screed for a durable, leak-free deck.
Landscaped & green roofs
Terrace gardens and planter zones where the membrane’s root resistance protects the slab beneath soil and irrigation.
Coastal & industrial
Exposed roofs in humid, aggressive atmospheres that need a tough, chemically stable elastomeric skin with strong concrete adhesion.
Roof refurbishment
Ageing RCC roofs re-waterproofed with a bonded liquid overlay, avoiding the cost and disruption of stripping the old system.
Frequently asked questions
What is the difference between ShaliUrethane LHM and LHM Plus?
How much LHM Plus do I need per square metre?
Does it need a primer and a top coat?
Can it take foot traffic?
Is it suitable for terrace gardens?
What pack size does it come in and how long does it store?
How we position STP ShaliUrethane LHM Plus
STP ShaliUrethane LHM Plus is Space Arc’s go-to single-component PU membrane for exposed roofs and podium decks where a seamless, root-resistant skin matters more than site-mixing convenience. It pairs naturally with its own STP family — ShaliPrime PUM or ShaliPrime 2E LC as primer, an aliphatic ShaliProtek 2AC PU TC top coat for UV colour stability, and ShaliProtek PU HA where the deck must carry foot traffic; for green roofs the root-resistant anti-root primer completes the build-up. Where the client specifies a two-component cold-applied system or a factory-UV-stable aliphatic finish, the ShaliUrethane LHM 2K and LM UV grades are the in-family step-ups. Across our other brands, Space Arc also supplies Fosroc, Dr. Fixit and MC-Bauchemie liquid membranes for projects standardised on those specifications — so the choice can follow the consultant’s approved-vendor list rather than force a switch.
Fosroc Nitoproof 800 — Specify the Fosroc option when the project is standardised on Fosroc or needs a factory UV-stable, trafficable exposed-deck PU system with a matched primer-membrane-topcoat build-up.
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