STP TarPlastic V
A cold-applied, non-sag bituminous caulking compound built for vertical joints, overlaps and cracks that ordinary horizontal-grade mastics simply slump off.
What is it?
A ready-to-use, cold-applied bituminous caulking compound loaded with mineral fillers in a volatile solvent, supplied as a black putty that stays plastic and grips vertical surfaces without sagging.
Where is it used?
Vertical and sloping joints on roofs and masonry: GI and asbestos sheet overlaps, J-hook and bolt heads, tiled-roof gaps, terrace cracks, parapets and masonry walls.
Why use it?
It seals moving joints where movement, vibration and heat would open up a rigid filler, while resisting flow and creep on the vertical face that defeats standard TarPlastic.
How is it applied?
Clean and prime the joint or V-cut crack with ShaliTex Primer, then press the putty in by hand, knife, spatula or trowel and overlap the crack by at least 25 mm each side.
About STP TarPlastic V
STP TarPlastic V is the vertical-grade member of STP Limited’s long-running TarPlastic caulking family. Where the standard grade is meant for horizontal terraces and flat gaps, the V grade is reformulated with mineral fillers and a controlled solvent balance so it holds its shape on walls, sloping roofs, sheet overlaps and parapet joints instead of flowing downward before it sets. It arrives as a black, ready-to-use putty that needs no heating, no mixing and no specialised plant on site, which makes it a practical field product for maintenance crews and roofing contractors working at height.
For engineers specifying repairs on GI and asbestos-cement roofs, or on tiled and terraced roofs across Delhi NCR and the rest of India, TarPlastic V fills a specific gap. It conforms to IS 1580-1991 and stays plastic for a considerable period after application, so it can absorb the everyday expansion, contraction and vibration that open up joints around fasteners and sheet laps. The skin and interior firm up over time to hold the seal, while the underlying compound keeps enough movement capacity to stop hairline gaps re-forming. Space Arc Engineering supplies it as an authorised STP distributor with technical guidance on primer selection and joint detailing.
The technical insight
The product works because it is a filled bituminous mastic that cures by solvent release rather than by chemical reaction. When applied, the volatile solvent begins to evaporate and the skin and outer layer stiffen, forming a firm cap over a core that stays plastic. The mineral fillers do two jobs here: they give the wet putty enough body and thixotropy to resist slump on a vertical face, and they build the internal structure that stops the compound creeping under its own weight or in summer heat. That balance is what separates TarPlastic V from a horizontal-grade filler. A flat-grade mastic relies on gravity holding it in the joint, so on a wall or sheet lap it sags and pulls away from the top edge. The V grade is tuned so surface tension and filler loading keep it in place long enough to set. Because the cured film retains long-term plasticity, it behaves as a low-modulus seal rather than a rigid plug, moving with the substrate through thermal cycling instead of debonding. The bituminous base also gives it inherent water resistance and, per STP, no harmful reaction on contact with drinking water, which is why it is trusted around domestic roof catchments.
Where it is used
- Sealing overlapping joints in GI and asbestos-cement roofing sheets
- Covering J-hook and holding-bolt heads under limpet washers on sheeted roofs
- Plugging gaps in tiled roofs caused by sagging battens or displaced tiles
- Filling minor cracks and gaps in terraced and concrete roofs
- Caulking vertical and sloping joints on masonry and parapet walls
- Sealing joints subject to expansion, contraction and vibration around fasteners
- General cold caulking on roofs where heating bitumen on site is impractical
- Waterproof spot-repairs at sheet-to-wall and flashing junctions
Key advantages
- Cold-applied and ready to use, so no heating kettles or on-site mixing
- Non-sag, filled formulation that resists creep and flow on vertical and sloping surfaces
- Stays plastic for a long period, accommodating expansion, contraction and vibration
- High resistance to heat, holding position through Indian summer roof temperatures
- Conforms to IS 1580-1991 for buyer and consultant assurance
- No specialised handling or skilled labour needed for application
- Inherently water-resistant with no harmful reaction on contact with drinking water
- Supplied in 1, 4, 20 and 200 kg packs to suit spot repairs through to large jobs
Limitations & considerations
- Solvent-based and inflammable, so it must be kept away from open flame and used with ventilation
- Cures by solvent evaporation, meaning full set takes about 72 hours for a 3 mm section and longer in thicker fills
- Not a high-movement structural joint sealant; use a polysulphide or PU for large dynamic joints
- Black bituminous finish only, with no colour options and possible staining of light substrates
- Requires a primer such as ShaliTex on rusted, dusty or porous joints for reliable adhesion
- Best on caulking-width cracks and laps, not a substitute for a full waterproofing membrane over large areas
Selection & best practice
Prepare the joint before anything else. On GI or asbestos sheet laps, clean out rust and loose material and apply a coat of ShaliTex Primer before working the compound into the overlap with a knife and spatula. For cracks, chase them out to a V-section about 25 mm deep, brush away loose particles, dust clean and prime lightly with ShaliTex Primer. Press TarPlastic V firmly into the primed crack by hand or trowel and finish by overlapping the crack by at least 25 mm on either side so the seal is anchored on sound substrate. When sealing J-hooks or holding bolts, cover the top of the bolt with the compound and set a limpet washer over it as a cap. Keep the container lid firmly closed when not in use to stop the solvent flashing off, store spare material in a cool, dry, shaded place, and use goggles and gloves during application, cleaning hands with warm soapy water afterwards. Allow the roughly 72-hour set for a 3 mm section before exposing the seal to standing water or heavy service.
Specifications
| Product type | Cold-applied bituminous caulking compound with mineral fillers, vertical grade |
| Form / Colour | Putty; Black |
| Standard | Conforms to IS 1580-1991 |
| Specific gravity | 1.2 |
| Penetration (25 C, 200 g, 5 sec) | 10 mm before setting; 8 mm after setting |
| Setting time (for 3 mm) | 72 hours |
| Recommended primer | ShaliTex Primer |
| Pack sizes | 1 kg, 4 kg, 20 kg and 200 kg containers |
| Storage | Cool, dry, shaded place in air-tight container, away from heat |
Industry use cases
Industrial and warehouse roofing
Sealing GI and asbestos-cement sheet overlaps and fastener heads on large shed roofs where laps open up under thermal movement.
Residential and terraced roofs
Cold spot-repair of minor cracks in terrace slabs and plugging tile gaps from sagging battens, without hot bitumen on an occupied building.
Facilities and building maintenance
Routine caulking of parapet, flashing and masonry joints on vertical faces during periodic waterproofing upkeep.
Institutional and commercial estates
Non-sag sealing around J-hooks and sloping roof junctions on schools, hospitals and offices where crews need a ready-to-use, low-skill product.
Frequently asked questions
How is TarPlastic V different from standard TarPlastic?
Does it need heating or mixing before use?
How long does it take to set?
Do I need a primer?
Which standard does it conform to?
What pack sizes are available and can Space Arc supply pan-India?
How we position STP TarPlastic V
TarPlastic V sits alongside standard STP TarPlastic in the same family: choose the V grade for vertical, sloping and overhead joints and the standard grade for horizontal terraces and flat gaps. Pair it with STP ShaliTex Primer, which STP specifies for surface preparation, and with STP’s wider bituminous range for full roof waterproofing rather than spot caulking. Where a job involves genuinely high-movement structural or expansion joints, step up to a Fosroc polysulphide or polyurethane gun-grade sealant from our Fosroc Nitoseal line instead of a bituminous mastic. Space Arc also stocks Dr. Fixit and Fosroc waterproofing systems for cases where a membrane or coating, not a caulk, is the right call.
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