STP TarPlastic AL
A ready-to-use, silver-pigmented cold bituminous caulk that seals roof, sheet and masonry joints while giving exposed work a cleaner, reflective aluminium finish.
What is it?
A single-component, cold-applied bituminous caulking compound in putty form, pigmented with aluminium to give a silver-grey finish instead of the usual black.
Where is it used?
Visible joints and gaps on metal roof sheets, folded sections and plates, concrete and masonry, and wooden members where a neater appearance is wanted.
Why use it?
It seals and stays flexible like standard bitumen caulk, but the silver pigment reflects more sunlight and looks far tidier on exposed surfaces than black mastic.
How is it applied?
Knifed or trowelled straight from the pack into clean, dry joints and grooves, then pressed firm to remove air pockets and tooled smooth. No mixing, heating or primer for most substrates.
About STP TarPlastic AL
STP TarPlastic AL is the silver-finished member of STP’s long-running TarPlastic family of bituminous caulking compounds. Chemically it is the same cold-applied, single-component putty that contractors have used for decades to seal holes, gaps and moving joints in roofs and masonry, but it carries an aluminium pigment that turns the normally jet-black paste a reflective silver-grey. That single change makes it the compound of choice wherever the sealed joint stays in view — sheet-roof laps, exposed plate and folded-section joints, parapet details and architectural masonry — because the finish blends with galvanised and aluminium roofing far better than a black smear and does not read as an afterthought on a finished elevation.
Functionally it behaves like the base TarPlastic. It arrives ready to use as a smooth, homogeneous paste, needs no heating or mixing, and is worked cold with a trowel or putty knife. Once placed it skins over on the surface while staying plastic underneath, so it accommodates the small thermal and vibration movements a roof joint sees through the day without cracking or pulling away. For Indian sites — long summers, monsoon exposure, metal roofs that expand and contract constantly — that combination of easy cold application, weather resistance and a tidy reflective finish is why specifiers reach for the AL grade rather than the standard black on anything that will be seen.
The technical insight
The compound is a bitumen base blended with mineral fillers and pigment, engineered to cure by solvent release and surface oxidation rather than by a chemical reaction. When you apply it, the exposed face slowly skins and toughens as light volatiles leave and the bitumen oxidises, while the body underneath stays soft and plastic. That two-state behaviour is the whole trick: the skin sheds water and resists weathering, and the plastic core keeps enough give to follow the joint as metal and masonry expand, contract and vibrate. Because it is a mastic and not an elastomer, it is best thought of as a caulk for low-movement gaps and laps rather than a structural movement-joint sealant — it seals and stays watertight, but it does not have the cyclic movement capability of a polysulphide or polyurethane. The aluminium pigment does more than look good: the reflective flakes bounce back a share of incident sunlight, so the exposed skin runs cooler and ages more slowly than the same compound in black, which on a sun-baked metal roof directly translates into a longer serviceable life for the seal.
Where it is used
- Sealing longitudinal and end laps on galvanised, Galvalume and aluminium metal roof sheets where the joint stays visible
- Caulking joints between folded metal sections, plates and flashings on industrial roofing and cladding
- Sealing gaps and cracks in exposed concrete and masonry parapets, copings and wall junctions
- Filling and sealing joints around wooden members, frames and battens
- Making good around roof penetrations, fasteners and overlaps that need a neat reflective finish
- Weather-sealing gutter, valley and ridge details on sheet roofs
- Touch-up and re-sealing of ageing bituminous joints on maintenance and refurbishment work
- Sealing porous concrete and masonry surfaces at floor, wall and roof junctions
Key advantages
- Single component and ready to use — no mixing, no heating, opens straight from the pack
- Cold-applied by trowel or putty knife, so it needs no torch, boiler or specialist plant on site
- Silver aluminium finish looks far tidier than black mastic on exposed and architectural joints
- Reflective pigment bounces back sunlight, helping the seal run cooler and age more slowly
- Non-sagging on vertical and sloped surfaces, so it holds shape in overhead and side laps
- Stays plastic under the skin, accommodating routine thermal and vibration movement without cracking
- Good adhesion across mixed substrates — metal, concrete, masonry and wood
- Backed by the field-proven TarPlastic formulation with a long track record on Indian roofs
Limitations & considerations
- It is a caulk, not an elastomeric movement-joint sealant — not suited to wide expansion joints with high cyclic movement
- Being bitumen-based, it is not paintable with most decorative topcoats and should not contact materials attacked by bitumen or its solvents
- Not intended for permanent water immersion or for potable-water contact
- Skinning and full toughening depend on air exposure, so it is unsuitable for deep, fully confined pours where the body cannot breathe
- Surfaces must be clean, dry and free of loose matter, oil and dust for the bond to hold
- Bituminous products can bleed or stain adjacent porous light-coloured finishes if not detailed carefully
Selection & best practice
Prepare the joint first: it must be clean, dry and free of dust, rust scale, oil and old flaking sealant, since the bond is only as good as the surface. Work the compound cold, pressing it firmly into the groove, lap or gap with a trowel or putty knife so no air is trapped behind it, then tool the face smooth to shed water. On wide or deep gaps, build up in passes and use a backing where appropriate rather than trying to bridge a large void in one placement — the compound needs air contact to skin properly. Apply in dry weather and let the surface skin before it is subjected to standing water or heavy rain. On highly porous concrete or masonry, or over dusty galvanised sheet, a test patch for adhesion is worth the few minutes it takes. Keep containers closed when not in use so solvent does not flash off in the pack, and store cool and away from open flame.
Specifications
| Product type | Cold-applied bituminous caulking compound (aluminium-pigmented grade) |
| Base chemistry | Bitumen blended with mineral fillers and aluminium pigment |
| Components | Single component, ready to use |
| Form | Putty / smooth homogeneous paste |
| Colour | Silver-grey (aluminium pigmented) |
| Application | Cold applied by trowel or putty knife; no heating or mixing |
| Sag resistance | Non-sagging on vertical and sloped surfaces |
| Indicative consumption | Approx. 1.25 kg per m² per 1 mm thickness (varies with joint depth) |
| Reference standard | TarPlastic family conforms to IS 1580 – 1991 |
Industry use cases
Industrial & warehouse roofing
Sealing visible sheet laps and folded-section joints on metal roofs where a black smear would spoil the finish and run hot under sun.
Commercial & institutional buildings
Caulking exposed parapet, coping and wall-junction joints on masonry facades where appearance matters to the client.
Maintenance & refurbishment
Re-sealing ageing bituminous joints and roof penetrations during upkeep, with a reflective finish that reads as new work.
Metal fabrication & cladding
Weather-sealing plate, flashing and folded-metal joints on fabricated roofing and cladding assemblies.
Water-conveyance & utility sheds
Sealing porous concrete and masonry joints on ancillary structures and roofs that need a tidy, weather-resistant caulk.
Frequently asked questions
How is TarPlastic AL different from standard TarPlastic?
Does it need heating or a primer before use?
Can I use it as an expansion-joint sealant?
Will it hold on vertical and overhead joints?
Is it suitable for constant water contact or drinking-water tanks?
How much should I order for my job?
How we position STP TarPlastic AL
Within the STP range, TarPlastic AL is the silver-finish upgrade of standard black TarPlastic — pick AL for exposed and architectural joints, black for concealed work. Where the roof needs full waterproofing rather than joint caulking, pair it with STP’s bituminous membrane systems such as SuperThermoLay APP rather than trying to extend a caulk beyond its role. When the joint actually moves — real expansion and construction joints — a bituminous mastic is the wrong tool; move to an elastomeric sealant. For dependable performance there, we most often specify Fosroc Thioflex 600 (movement joints in concrete and masonry) or Fosroc Nitoseal MS600 (immersed and water-retaining joints). Space Arc supplies all of these, so we can match the right chemistry to the joint rather than forcing one product to do every job.
Fosroc Thioflex 600 — Specify Thioflex 600 instead of a bituminous caulk when the joint genuinely moves and needs a cold-applied polysulphide elastomer with real cyclic movement capability and long service life.
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