STP TarFelt LM
Brush, roll or spray it on — STP’s cold-applied liquid membrane seals sunken slabs, terraces, tin roofs and basement walls, torch-free.
What is it?
A ready-to-use, acrylic-modified bituminous liquid membrane you apply cold — no torch, no heating.
Where is it used?
Sunken toilet/kitchen slabs, terraces, sub-grade walls, tin/AC roofs, and rejuvenation of old Hessian or HMHDPE membranes.
Why use it?
A seamless, crack-bridging (up to 1.5 mm) black membrane that bonds to slightly damp concrete without the fire risk of torch-applied felt.
How is it applied?
Primed with a 50:50 TarFelt LM–water mix, then two coats at 0.70 kg/m² sandwiching a 45 GSM fibreglass mesh (1000-micron DFT on decks); lighter 0.20 kg/m² coats on vertical sub-grade walls.
About STP TarFelt LM
STP Limited has spent over eight decades building India’s waterproofing vocabulary, and TarFelt is the bituminous membrane family most site engineers know by name. Where TarFelt APP, BH, BS and FG are torch-applied felt rolls, heat-welded seam by seam, TarFelt LM breaks that pattern. It’s a ready-to-use, acrylic-modified bituminous emulsion that goes on with a brush, roller or airless spray gun, cures in open air, and dries to the same black, monolithic skin a torch membrane leaves — minus the flame, the gas cylinder, and the skill it takes to weld a clean overlap.
That makes LM the practical pick where a torch is inconvenient or unsafe — sunken toilet and kitchen slabs threaded with plumbing, tin and corrugated-asbestos roofs that can’t take direct flame, and re-roofing jobs where stripping an old Hessian or HMHDPE membrane isn’t worth the labour. It’s forgiving of a slightly damp substrate too, which matters on sites racing a monsoon deadline. The trade-off: a proper spec still needs a primer pass, two body coats and an embedded fibreglass mesh to reach its rated 1000-micron DFT. It’s a system to install correctly, not a one-coat shortcut.
The technical insight
Strip away the branding and TarFelt LM is a water-based bitumen-acrylic hybrid — specific gravity 1.1 ± 0.02 at 30°C, Brookfield viscosity 4000 ± 500 cps, thick enough to hold film on a slope without heavy thinning. The cured-film numbers (14-day, 1.5 mm film) matter more: 200-240% elongation and 1.20 ± 0.1 MPa tensile strength per ASTM D-412 put it in the same flexibility bracket as many acrylic roof coatings. A 1.5 mm crack-bridging rating under ASTM C-836 handles shrinkage hairlines and moderate thermal movement, but not a live structural or expansion joint — that still needs a dedicated sealant. Pull-off adhesion of 1.2 MPa (ASTM D-4541) and Shore A hardness above 50 explain why STP specifies a sand broadcast and protective screed over it rather than leaving it exposed.
Where it is used
- Sunken toilet and kitchen slabs where plumbing rules out a torch
- Sub-grade concrete and basement retaining walls before backfilling
- Corrugated asbestos, metal and non-galvanised tin roof sheeting
- Rejuvenating aged Hessian or HMHDPE terrace membranes without a full tear-off
- Residential flat and sloped terraces as a torch-free felt alternative
- Podium decks and planter boxes ahead of a protective screed
Key advantages
- No torch or LPG cylinder on site — cuts fire-permit hassle and reliance on skilled felt-welders
- Bonds to concrete that’s still slightly damp, useful on monsoon-deadline sites
- Cures into a genuinely seamless film with no heat-welded overlaps to fail later
- 1.5 mm crack bridging plus 200-240% elongation gives real tolerance for hairline shrinkage cracking
- Water-based and low-odour to apply compared with solvent-borne liquid membranes
- Doubles as a vapour barrier on sunken slabs and sub-grade walls prone to rising damp
- Cured film resists fungus and algae growth, a common complaint on old felt terraces
Limitations & considerations
- A multi-step system — primer, two coats and an embedded mesh are all needed to hit the rated DFT, so labour time adds up
- 1.5 mm crack bridging suits shrinkage cracks, not active structural or expansion joints
- Being water-based, it needs a genuinely dry window to cure; heavy rain on a fresh, uncured coat can compromise the film
- No potable-water certification on the data sheet, so it isn’t the product for a drinking-water tank interior
- Sold only in a 20 kg pack — no small tin for a one-off balcony patch job
Selection & best practice
Follow STP’s sequence rather than shortcutting it. Grind the deck clean, V-groove and fill cracks with a ShaliCrete:cement:sand (1:2:5) mortar, and turn a 50 mm coving at every wall junction before touching the membrane. Stir TarFelt LM at low speed and let it stand so trapped air escapes. On decks: dampen the surface, prime with a 50:50 TarFelt LM–water mix at 400 gm/m², then apply two coats at 0.70 kg/m² each, embedding a 45 GSM fibreglass mesh between them with 50 mm overlaps while still tacky. On vertical sub-grade walls, skip the mesh and use 0.20 kg/m² per coat. Allow 36 hours before follow-on work and run a 7-day ponding test before sign-off.
Specifications
| Chemistry | Acrylic-modified bituminous emulsion, water-based, single component |
| Specific Gravity (@30°C) | 1.1 ± 0.02 |
| Viscosity (Brookfield, @25°C) | 4000 ± 500 cps |
| Elongation at break (14-day cure, 1.5 mm film, ASTM D-412) | 200 – 240% |
| Tensile Strength (14-day cure, ASTM D-412) | 1.20 ± 0.1 MPa |
| Crack Bridging (ASTM C-836) | Up to 1.5 mm |
| Pull-off Adhesion (ASTM D-4541) | 1.2 MPa |
| Water Absorption | < 1% |
| Pack Size / Shelf Life | 20 kg pack; 12 months in sealed condition |
Industry use cases
Residential Renovation
Sunken toilet/kitchen slab waterproofing during bathroom remodels, where a torch can’t safely go near tight plumbing runs.
Basement & Sub-structure
Vertical damp-proofing on sub-grade retaining walls before backfill, at the lighter 0.20 kg/m² vertical dosage.
Industrial Roofing
Re-coating corrugated asbestos, metal or non-galvanised tin roof sheets on factory sheds and warehouses.
Terrace Rejuvenation
Overlaying aged Hessian- or HMHDPE-based membranes on leaking terraces that aren’t worth a full strip-and-relay.
Frequently asked questions
Does TarFelt LM need a torch or gas heating to apply?
How many coats does a proper installation actually need?
Can it go on a slightly wet surface, or does the deck need to be bone dry?
How soon can we plaster over it or let it take foot traffic?
How much area does one 20 kg pack cover?
Is it suitable for waterproofing an overhead or underground drinking water tank?
How we position STP TarFelt LM
TarFelt LM sits alongside STP’s torch-applied TarFelt APP, BH, BS and FG membranes as the cold-applied option in the same family, and its own application method leans on other STP products — ShaliCrete for crack repair, ShaliPlast IW in the protective screed, ShaliGeoText as the protection layer — so a single-brand deck build is genuinely possible. Where a job needs a fully moisture-cured polyurethane membrane instead, typically below-grade work under real hydrostatic pressure, Fosroc’s Nitoproof 600 is the credible alternative a specifier would weigh against it. Space Arc stocks and applies both, so the choice comes down to the deck and the budget, not brand loyalty.
Fosroc Nitoproof 600 — A specifier chasing a fully moisture-cured polyurethane membrane for below-grade or hydrostatic-pressure conditions, rather than a bitumen-acrylic system, would lean toward Fosroc Nitoproof 600 instead.
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