STP ShaliSeal BT MJ
Single-component, cold-applied elastomeric bitumen sealant that keeps metal sheet laps, ridges and flashing joints watertight through years of thermal movement.
What is it?
A ready-to-use, single-component bituminous elastomeric sealant from STP, formulated specifically for sealing overlaps and joints in metal roofing and cladding.
Where is it used?
Metal sheet roofs, factory sheds, ridge and flashing lines, gutter laps, ducting and jacketed insulation joints across industrial and commercial buildings.
Why use it?
It stays flexible from -40C to +125C, bonds tightly to steel and aluminium, and resists sun, rain and thermal cycling without cracking or running.
How is it applied?
Applied cold, straight from the pail, by trowel or spatula onto a clean, dry joint. No heating, no mixing and no primer gun required.
About STP ShaliSeal BT MJ
ShaliSeal BT MJ, previously catalogued by STP as ShaliSeal MJ, is a purpose-built joint sealant for the one problem that quietly ruins metal roofs: the overlap. Wherever two profiled sheets meet, or where a ridge cap, flashing or gutter is fixed, the fastener line and the lap become the point that leaks first. This product is a single-component, cold-applied elastomeric compound with a bitumen base and an aluminium-grey, high-viscous pasty consistency that lets it sit in a joint without slumping while still moving with the substrate.
The material is engineered around the way sheet metal behaves in the Indian climate. A steel or aluminium roof can swing through a wide temperature band between a summer afternoon and a monsoon night, and that daily expansion and contraction is exactly what fatigues a rigid seal. ShaliSeal BT MJ remains serviceable from -40C to +125C and keeps its elasticity across that range, so the seal flexes with the panel instead of tearing away from it. Because it arrives ready to use in a 20 kg pail and needs no torch or two-part mixing, it suits both new erection work and quick remedial sealing on an occupied building.
The technical insight
The performance comes from a rubberised bitumen matrix that behaves as an elastomer rather than a hard mastic. Bitumen gives it inherent water repellency and excellent wetting of oily, mill-finished metal; the rubber and polymer content give it the recovery to stretch and return as the joint cycles. On application it is a soft, workable paste with over 60% solids by weight, so it can be tooled firmly into a lap and around fastener heads. It touch-dries in around 25 minutes as solvent flashes off, then continues to build strength over roughly 48 hours, forming a tough, continuous skin that grips both faces of the joint. Because the cure is physical rather than a moisture reaction, it is forgiving of the thick, non-uniform bead thicknesses that real sheet-metal laps demand, and it stays bonded through the constant micro-movement that would open up a brittle sealant.
Where it is used
- Sealing longitudinal and end overlaps of profiled steel and aluminium roofing sheets
- Ridge cap, hip and valley joints on metal roofs where cap meets sheet
- Flashing, apron and parapet-to-roof junction sealing
- Gutter laps, downpipe junctions and rainwater channel joints
- Metal cladding and wall-panel side and end laps
- Sealing around roof fasteners, screw heads and stitching lines
- Joints in metal ducting, cowls and jacketed thermal insulation
- Terminating and lapping bitumen-based roofing membranes against metal trims
Key advantages
- Single component and cold-applied, so no mixing, heating or specialist plant on site
- Stays elastomeric from -40C to +125C, moving with the sheet instead of cracking
- Strong adhesion to steel, aluminium and even mill-oiled metal surfaces
- High-viscous pasty body holds its shape in vertical and overhead laps without slumping
- Weatherproof against sun, rain and cyclic temperature, with good chemical resistance
- Ready to use from the pail, ideal for both new works and fast remedial sealing
- Bitumen base is compatible with asphaltic and bituminous membranes and flashings
- Touch-dry in about 25 minutes, letting crews move along a roof quickly
Limitations & considerations
- Solvent-based and flammable with a flash point above 23C, so keep away from naked flame and ensure ventilation during application
- Aluminium-grey and not colour-matched; it is a functional seal, not an architectural finish, and is best kept out of prime sightlines
- Must not be applied to damp, wet or frosted joints, or during rain, as the bond depends on a dry surface
- Depth of the sealed joint should not exceed its width, so very deep or wide gaps need correct joint design or backing rather than over-filling
- As a bituminous compound it is not intended for potable-water contact or for the movement joints of a facade, where a PU or MS-polymer sealant is the right choice
Selection & best practice
Start by preparing the joint properly, because this sealant is only as good as the surface under it. Remove dirt, oil, grease, rust scale and loose coatings by dry-air jet and mechanical cleaning or light grinding until you reach sound, dry metal, and never apply over a damp or wet lap. Work in dry weather with adequate ventilation and keep the material clear of any open flame given its solvent content. Apply the paste evenly with a trowel or spatula, pressing it firmly into the overlap and around every fastener head so there are no voids, and keep the sealed depth no greater than the joint width. Tool off excess for a clean, continuous bead, allow the roughly 25-minute touch-dry before disturbing it, and protect fresh work from rain until it has set over about 48 hours. Store unused material in its sealed 20 kg pail in a cool, dry place away from heat, where it keeps for up to 12 months.
Specifications
| Product type | Single-component, cold-applied elastomeric bituminous metal-joint sealant |
| Colour / consistency | Aluminium grey; high-viscous, pasty |
| Service temperature | -40C to +125C |
| Specific gravity | 1.20 plus/minus 0.2 |
| Solid content | >60% by weight |
| Touch-dry time | Approx. 25 minutes |
| Setting time | Approx. 48 hours |
| Flash point | >23C |
| Pack size / shelf life | 20 kg container; 12 months in sealed condition |
Industry use cases
Industrial sheds & factories
Sealing sheet laps, ridges and fastener lines on large PEB and metal-roof factory buildings where thermal movement is severe and downtime for leaks is costly.
Warehousing & logistics
Watertight sealing of long-span metal roofs, gutters and flashings on distribution centres and cold-store envelopes.
Commercial & retail rooftops
Remedial and new-build sealing of ridge caps, parapet flashings and rooftop plant penetrations on metal-clad malls and showrooms.
Infrastructure & MEP
Sealing joints in metal ducting, cowls and jacketed insulation, and lapping bituminous membranes against metal trims in services work.
Frequently asked questions
Do I need to heat or mix ShaliSeal BT MJ before use?
What is the coverage from a 20 kg pack?
Can I apply it on a metal roof that is still slightly wet?
Will it bond to both galvanised steel and aluminium sheets?
Is it suitable for facade expansion joints or glazing?
How long before it is rain-safe, and how should I store the rest?
How we position STP ShaliSeal BT MJ
ShaliSeal BT MJ is the STP answer for metal roof and cladding lap sealing. Within the STP range, pair it with ShaliSeal BT SB, a rubberised solvent-based bituminous sealing compound, for concrete-to-metal and general bituminous joints, and reach for a polyurethane grade such as ShaliUrethane BTD where a gun-grade movement-joint sealant is needed rather than a trowel-applied metal mastic. For bitumen-membrane roofing work that ties into these metal joints, STP’s ShaliBond and bituminous primer lines are natural companions. Where a client specifies Fosroc, we supply the equivalent Fosroc products from the same warehouse, so the choice stays about the right chemistry for the joint rather than brand availability.
Fosroc Nitoseal MB175 — Specifiers standardised on Fosroc can choose Nitoseal MB175, a gun-grade rubber-bitumen sealant for the same sheet laps, flashings and gutter joints, when they prefer a cartridge/gun application over trowel-applied mastic.
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