STP TarFelt BS
The classic hessian-and-bitumen roofing felt behind thousands of Indian godowns, silos and factory sheds — honest, economical waterproofing for non-critical, over-ground roofs.
What is it?
A first-generation, hot-applied bituminous waterproofing membrane: a hessian (jute) fabric core coated on both faces with oxidized bitumen, with a mica or sand dusting so the rolled sheet doesn’t stick to itself in storage.
Where is it used?
RCC and corrugated AC/GI sheet roofs of warehouses, factory sheds, grain godowns and silos, and historically on wagon, tram and bus-body roofs — essentially any over-ground, non-critical surface needing basic waterproofing on a tight budget.
Why use it?
It’s one of the most economical membranes in STP’s waterproofing range, backed by decades of field use on Indian industrial sheds, where a straightforward 5-8 year service life is an acceptable trade-off for low first cost.
How is it applied?
Primed with ShaliTex Primer, hot-bonded to the deck with STP Bitumen 85/25 at roughly 1.2 kg/m² per coat, unrolled with 75-100 mm overlaps sealed in hot bitumen, and topped with stone grit, pea gravel or reflective aluminium paint.
About STP TarFelt BS
TarFelt BS is about as traditional as bituminous waterproofing gets in the Indian market. It’s built the way roofing felt has been made for generations — a woven hessian (jute) fabric is coated on both faces with oxidized bitumen, then dusted with mica or fine sand so the rolled sheet doesn’t fuse to itself in storage. There’s no polymer modification here, no APP or SBS chemistry pushing up the price; it’s a straight, hot-applied bitumen felt, and STP prices and positions it accordingly.
That simplicity is the whole point. On a factory shed roof, a grain godown, or a low-rise industrial structure where budgets are tight and the roof isn’t expected to double as a trafficable or landscaped deck, TarFelt BS gives a proven, workable waterproofing course without paying for performance the application doesn’t need. STP’s own literature notes it has historically been used on wagons, trams and bus bodies as well as buildings — a sign of how long this specification has been in service. Space Arc supplies and applies TarFelt BS across Delhi NCR for exactly this bracket of project, alongside STP’s higher-spec modified-bitumen and TPO membranes for anything more demanding.
The technical insight
TarFelt BS is defined by its reinforcement and binder rather than any additive. Hessian is a coarse jute weave that gives the felt tensile strength — 100 kg warp / 50 kg weft per STP’s own figures — and pliability down to 15°C, but it doesn’t match the puncture resistance or dimensional stability of the glass-fibre or polyester carriers used in modern APP/SBS membranes. The binder is oxidized (blown) bitumen, not a polymer-modified bitumen, which is why the data sheet rates “no flow” only up to 68°C — a narrower service window than a modified membrane, and the reason this felt suits non-critical, over-ground roofs rather than podium decks or water tanks.
Where it is used
- RCC roof slabs on warehouses, factory sheds and industrial buildings
- Grain godown and silo roof waterproofing
- Overlay waterproofing onto corrugated AC/GI sheet roofing
- Timber and shell/folded-plate roof waterproofing
- Wagon, tram and bus-body roof waterproofing
- Budget residential and low-rise terrace waterproofing
- Interim waterproofing during phased or staged construction
- Base ply in multi-layer built-up bituminous roofing systems
Key advantages
- Decades-proven, well-understood membrane system, not an unverified chemistry
- One of the most economical waterproofing options in STP’s own range
- Good pliability — wraps contours and upstands without cracking down to 15°C
- Fully hot-bonded membrane construction, with no cold adhesive layer to fail
- Simple, well-documented application method most local waterproofing crews already know
- Applicable over concrete, AC/GI sheet, timber and shell/folded-plate roofs
- Meets STP’s own 300 mm pressure-head and 68°C heat-resistance factory tests
- Low water absorption for a conventional felt of this class — 2% max
Limitations & considerations
- STP itself markets it as a ‘first generation,’ limited-life membrane — not intended for critical or long-warranty applications
- Oxidized bitumen has a narrower working-temperature range than APP/SBS modified-bitumen membranes
- Hot-bitumen application needs an on-site heating kettle, so fire-safety precautions and skilled labour are essential
- Hessian reinforcement is weaker and less puncture-resistant than the glass-fleece or polyester carriers used in premium membranes
- Not intended for basements, water tanks, podium decks or other critical/below-grade waterproofing
- The TDS does not cite an IS/ASTM/BS/EN standard number — confirm current certification with STP before tendering
Selection & best practice
Prime the deck with ShaliTex Primer at a minimum of 0.25 L/m² and let it cure fully before laying felt. Bond with STP Bitumen 85/25, heated to working temperature and spread uniformly at about 1.2 kg/m² per coat — poor bitumen-temperature control is the single most common cause of adhesion failure on site. Unroll TarFelt BS with hand pressure to expel trapped air, keep overlaps to 75 mm along the length and 100 mm across, and seal every joint in hot bitumen. Always finish with a protective layer — stone grit or pea gravel in hot bitumen for exposed roofs, or a bituminous aluminium paint for non-trafficable ones — and stagger joints on any multi-layer treatment.
Specifications
| Reinforcement | Hessian (jute) fabric core, bitumen-coated both faces |
| Facing | Mica / sand dusting on both surfaces (anti-stick) |
| Breaking Strength – Warp | 100 kg, min |
| Breaking Strength – Weft | 50 kg, min |
| Weight per Roll | 35 kg, min |
| Bitumen Content per Roll | 18 kg |
| Water Absorption | 2%, max |
| Heat Resistance | No flow at 68 ± 2°C for 3 hours |
| Roll Size / Pack | 1 m x 20 m (20 m² per roll) |
Industry use cases
Industrial & Warehousing
Economical roof waterproofing for factory sheds, warehouses and distribution roofs, typically finished with stone-grit or aluminium-paint protection.
Agri-storage
Grain godown and silo roof waterproofing, where TarFelt BS’s traditional specification and low cost suit large-footprint agricultural infrastructure.
Transport & Rolling Stock
Roof waterproofing for railway wagons, trams and bus bodies — an application STP has specified for this felt since its early years.
Budget Residential / Low-Rise
Terrace waterproofing on cost-sensitive residential and low-rise commercial buildings where a 5-8 year membrane life is an acceptable trade-off for price.
Retrofit over AC/GI Sheeting
Overlay waterproofing on ageing corrugated asbestos-cement or GI sheet roofs ahead of re-roofing, or as an interim fix.
Frequently asked questions
Is TarFelt BS the same as STP’s TarFelt APP or modern SBS membranes?
What service life should I expect from TarFelt BS?
Can TarFelt BS be applied cold, without a bitumen kettle on site?
Does TarFelt BS need a protective top layer, or can it be left exposed?
How many layers of TarFelt BS should I specify?
Is TarFelt BS suitable for a basement or water tank?
How we position STP TarFelt BS
Within STP’s own felt range, TarFelt BS is the entry point: TarFelt FG and BH step up to heavier hessian or glass-fibre constructions for tougher exposure, while TarFelt APP and TarFelt LM move into polymer-modified (APP/SBS) bitumen membranes with a wider service-temperature range and longer expected life, at a proportionately higher price. For basements, podium decks, or any project needing a long manufacturer warranty, specifiers typically step up to STP’s modified-bitumen or ShaliTPO membranes, or look at a competing modified-bitumen/self-adhesive system such as Fosroc’s Proofex range — Space Arc can quote either route depending on your budget and exposure.
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