STP ShaliPrime S
Two-component epoxy joint primer that anchors polysulphide and polyurethane sealants to concrete, steel, aluminium, glass and wood — so the joint fails on movement design, never on adhesion.
What is it?
A low-viscosity, 1:1 two-component epoxy primer from STP Ltd (formerly ShaliSeal Primer), formulated with adhesion promoters for sealant joint faces.
Where is it used?
Movement and construction joints in concrete, aluminium- and steel-to-concrete gaps, and glass-to-aluminium cavities, ahead of polysulphide or PU sealant.
Why use it?
Most joint reseals trace back to bond-line failure, not the sealant. A primed face turns sealant peel and water ingress into a solved problem.
How is it applied?
Mix the two packs 1:1, brush or roll a thin coat onto prepared joint faces, then gun the sealant on while the primer is still tacky — about 30 minutes.
About STP ShaliPrime S
Ask any waterproofing applicator why a sealed expansion joint leaked within two seasons and the answer is rarely the sealant itself — it is the bond line. Polysulphide and polyurethane sealants shrug off movement and immersion, but only if they stay stuck to the joint arris. ShaliPrime S, which older site hands will remember as ShaliSeal Primer, is STP Ltd’s answer to that weak link: a two-component epoxy carrying adhesion-promoting ingredients, thinned to a viscosity that soaks into the concrete pore structure rather than sitting on it. One material primes for both polysulphide and PU systems, across concrete, steel, aluminium, glass and wood.
Space Arc Engineering supplies genuine STP material with current-batch documentation, in the 1 L pack that suits joint-repair gangs and the 12 L pack for project quantities. We support bridge, water-retention and facade contractors across Delhi NCR with pan-India dispatch, and can advise on the full joint build-up — primer, backer and sealant — against your specification.
The technical insight
The chemistry works in two stages. First, the low-viscosity epoxy penetrates the capillary pores of the joint face, binding friable material at the arris and presenting the adhesion promoters — reactive groups that couple to both mineral and metallic substrates — right at the surface. Second, timing does the rest: the sealant is applied while the primer is tacky, still carrying unreacted epoxy sites, so the curing sealant links chemically into the primer film instead of merely touching it. The joint then fails cohesively (within the sealant, by design) rather than adhesively (peeling off the face). This is also why the TDS is blunt about the window — once the film goes fully tack-free, those reactive sites are consumed and a glassy, closed surface remains. Re-priming is then mandatory, not optional.
Where it is used
- Joint-face priming before polysulphide sealant in expansion and movement joints
- Priming ahead of polyurethane sealants in building and infrastructure joints
- Aluminium- and steel-to-concrete gaps around frames, anchors and embedded plates
- Glass-to-aluminium cavities in glazing and facade sealing work
- Concrete nosings of bridge and flyover deck joints prior to resealing
- Joints in water-retaining structures sealed with polysulphide systems
- Precast element and masonry joints where substrate porosity threatens sealant bond
- Sealant priming over wood and glass in joinery and shopfront details
Key advantages
- Low viscosity penetrates porous concrete arrises instead of filming over dust-blocked pores
- One primer serves both polysulphide and PU sealant systems — simpler site inventory
- Foolproof 1:1 ratio, and it holds by volume or by weight
- Bonds to concrete, steel, aluminium, glass and wood — covers mixed-substrate joints
- Brush or roller application with no specialist equipment
- Sealant follows in about 30 minutes, so caulking gangs keep moving
- Economical: 6–8 m²/L on concrete rises to 9–11 m²/L on metal faces
- 1 L pack matches small resealing jobs without wasting a part-used kit
Limitations & considerations
- Sealant must go on while the primer is tacky; a tack-free face must be re-primed, so mis-sequenced gangs pay twice
- Application limited to 10–40 °C with relative humidity below 75% — humid monsoon afternoons are out
- Once Components A and B are mixed the whole quantity starts curing; mix only what the crew can place
- It is a primer, not a sealant — joint movement capacity still depends entirely on the sealant selected
- Demands sound, dry, mechanically prepared faces; it will not bind laitance, dust or damp concrete
- Epoxy vapours and skin-contact risk make ventilation, gloves and eye protection non-negotiable
Selection & best practice
Preparation decides the outcome. Scarify or grit/sand-blast the joint faces, remove every trace of laitance and loose particles, and take off oil or grease with 60-grit paper, roughening to a 3–4 mil profile. Add the entire Component B into Component A — never split packs by eye — and mix for three minutes with a slow-speed drill at 400–500 rpm fitted with a proper paddle until the mix is uniform. Apply a thin, continuous coat by brush or roller to both joint faces. Let it dry for around 30 minutes and gun the polysulphide or PU sealant on while the film is still tacky; plan the priming run so the sealant crew is never more than half an hour behind. If any primed length goes tack-free unsealed, re-prime it before sealing. Check substrate temperature (10–40 °C) and humidity before starting, not after.
Specifications
| Composition | Two-component epoxy with adhesion promoters (Comp A clear, Comp B light brown) |
| Mixing ratio | 1:1 by volume or weight |
| Mixed density | 0.96 ± 0.02 g/cc |
| Theoretical coverage, concrete | 6–8 m²/L (surface- and porosity-dependent) |
| Theoretical coverage, metal | 9–11 m²/L |
| Waiting time before sealant | ~30 minutes — apply sealant while tacky |
| Application conditions | 10–40 °C; RH below 75% |
| Packing | 1 L and 12 L unit packs |
| Shelf life | 12 months in original unopened, sealed packs |
Industry use cases
Bridges & Flyovers
Deck joint resealing where traffic-induced movement peels unprimed sealant off concrete nosings — priming shifts the failure mode back into the sealant’s design range.
Water Infrastructure
Reservoirs, WTP/STP basins and canal structures running polysulphide joints under permanent immersion, where a re-entry for joint repair is costly and disruptive.
Buildings & Facades
Aluminium-frame-to-concrete perimeters and glass-to-aluminium cavities in curtain wall packages, where the joint crosses three different substrates.
Industrial Plants
Joints at steel embedments, machine plinths and precast interfaces where PU sealants must grip both metal and concrete in one run.
Metro & Urban Transit
Station and precast segment joints sealed in night blocks — the 30-minute prime-to-seal window fits tightly sequenced gang work.
Frequently asked questions
Is a primer genuinely necessary before polysulphide sealant?
How long after priming can the sealant go on, and what if we miss it?
How much ShaliPrime S should I budget for a joint run?
Can it be used under sealants from other manufacturers?
What surface preparation does the joint face need?
What packs are available and how long can we hold stock?
How we position STP ShaliPrime S
ShaliPrime S is the opening move of STP’s joint-sealing system: follow it with ShaliSeal PD/PS polysulphide for immersed and trafficked joints, or ShaliSeal PU where the specification calls for polyurethane — Space Arc stocks the sealants alongside the primer so the whole build-up arrives as one warranted system. On Fosroc-specified projects we supply the parallel pairing: Thioflex 600 polysulphide for structural movement joints and Primer 20 with Colpor 200PF on pavement work. Mixed-spec sites can therefore draw every joint component — primer, sealant and technical backup — from a single counter.
Fosroc Primer 20 — Specifiers running a Fosroc joint system — typically Colpor 200PF polyurethane on roads, runways and hardstandings — choose Primer 20 so primer and sealant sit under one manufacturer’s compatibility warranty.
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