STP ShaliBond GCW 340
The two-component epoxy impregnating primer that seals and keys concrete before a carbon or glass fibre wrap goes on.
What is it?
A two-component, thixotropic, penetrative epoxy primer-cum-sealer from STP (formerly ShaliWrap Primer) that forms the first coat of an FRP structural strengthening system.
Where is it used?
On prepared concrete beams, columns, slabs and bridge elements that are about to be wrapped with carbon or glass fibre fabric for strengthening or seismic retrofit.
Why use it?
It penetrates and seals the porous concrete surface and creates a high-bond epoxy key, so the saturant and fibre wrap that follow develop their full designed adhesion to the substrate.
How is it applied?
Mix the two packs in the supplied ratio, then brush or roller-apply a uniform coat onto the sound, dry, prepared surface and let it become tacky before applying the epoxy saturant and fabric.
About STP ShaliBond GCW 340
ShaliBond GCW 340 is STP Limited’s epoxy impregnating primer for fibre-reinforced-polymer (FRP) strengthening work, and it is the product you will find listed under its earlier name, ShaliWrap Primer. In an FRP wrap system, the fabric does the structural work only if it is bonded to the concrete through an unbroken chain of epoxy layers. GCW 340 is the base of that chain. It is a two-component, cold-cure epoxy that is deliberately made thixotropic and penetrative, so it soaks into the open pores of the concrete, seals the surface against the dust and micro-voids that would otherwise starve the bond, and leaves behind a resin-rich film that the next layer keys straight into.
For engineers and applicators, that makes GCW 340 a small line item with an outsized influence on whether a strengthening job performs. It sits below the saturant coat (STP’s ShaliBond GCW 310, formerly ShaliWrap Saturant) and the carbon or glass fabric, and it is what turns a rough, absorbent concrete face into a stable, sealed, high-adhesion surface. Space Arc supplies GCW 340 as an authorised STP distributor and applies it as part of full FRP retrofit packages across Delhi NCR and pan-India, so specifiers can source the primer, the saturant and the fabric as one coherent, single-source system rather than mixing incompatible brands across the layers.
The technical insight
The reason a dedicated primer exists at all comes down to how epoxy bonds to concrete. A concrete surface, even after grinding, is porous and full of laitance and fine air voids; if you applied a thick, high-viscosity saturant straight onto it, that saturant would bridge over the pores instead of filling them, trapping air at the interface and leaving the bond to fail at a fraction of its rated strength. GCW 340 is formulated the opposite way: low enough in body to wick into the pore structure and impregnate the top layer of the concrete, yet thixotropic so it holds on vertical and overhead surfaces without sagging or running off a column face. As the two components cure together they polymerise into the concrete rather than just onto it, sealing the substrate and forming a continuous resin surface. When the saturant and fabric are then applied wet-on-tacky, the whole assembly cross-links into one monolithic epoxy-fibre laminate, which is exactly the load path the strengthening design assumes.
Where it is used
- Primer coat for carbon (CFRP) and glass (GFRP) fabric strengthening of concrete beams and columns
- Surface sealing and keying ahead of an epoxy saturant in a wet lay-up FRP system
- Seismic retrofit and confinement of RC columns by fibre wrapping
- Flexural and shear strengthening of slabs and bridge girders
- Column and pier jacketing with composite wrap
- Strengthening of structures whose loads have increased due to change of use or added storeys
- Rehabilitation of members with reduced capacity from corrosion or ageing
- Preparation of concrete substrates in confined or hard-to-form locations where added dead load must be avoided
Key advantages
- Penetrates and seals porous concrete, giving the fibre system its full designed bond strength
- Thixotropic body stays put on vertical and overhead faces without sagging
- Cold-cure, two-component chemistry needs no heat or special curing plant on site
- Part of a matched STP FRP system, so primer, saturant and fabric are chemically compatible
- Brush or roller application suits confined retrofit spaces that formwork cannot reach
- Adds negligible dead load compared with concrete or steel strengthening jackets
- Sourced and applied through a single authorised STP channel with technical backup
- Suits both carbon and glass fibre wraps, so it fits a range of strengthening designs
Limitations & considerations
- It is only the primer stage; on its own it provides no structural capacity without the saturant and fibre fabric
- Bond quality depends entirely on correct surface preparation, sound substrate and a dry, clean face
- Being epoxy, it is sensitive to low temperature and high humidity during cure and needs a workable overcoat window
- Substrate moisture and laitance will compromise adhesion if not removed before priming
- Mixed material has a limited working (pot) life once the two components are combined
- Requires trained applicators and PPE; uncured epoxy is a skin and respiratory sensitiser
Selection & best practice
Treat GCW 340 as the make-or-break step, not a formality. Start with a structurally sound substrate: remove all unsound concrete, expose and treat corroded steel, and grind back laitance to a clean, open surface, then make good any profile so the face is smooth and continuous. The concrete must be dry and dust-free before priming. Mix the base and hardener thoroughly in the ratio STP specifies, mixing only what can be used within the pot life, and apply a uniform coat by brush or roller with no misses on vertical and soffit areas. Then follow STP’s recoat guidance closely: the saturant and first fabric layer are applied while the primer is still tacky so the layers chemically fuse. Work within sensible ambient temperature and humidity limits, keep the primed area protected from dust and rain until overcoated, and confirm the exact consumption rate, pot life and overcoat times from the current STP technical data sheet for your project conditions.
Specifications
| Product type | Two-component (2K) thixotropic penetrative epoxy impregnating primer-cum-sealer coat |
| Brand | STP Limited |
| Former name | ShaliWrap Primer |
| Base chemistry | Epoxy resin + hardener, cold cure |
| Consistency | Thixotropic (non-sag on vertical / overhead surfaces) |
| Function in system | Primer / sealer coat beneath epoxy saturant and carbon or glass fibre fabric |
| Substrates | Concrete beams, columns, slabs and bridge elements |
| Application method | Brush or roller |
| System partners | ShaliBond GCW 310 saturant (formerly ShaliWrap Saturant) + CFRP / GFRP fabric |
Industry use cases
Bridges & Infrastructure
Priming girders, piers and deck soffits before CFRP wrapping to restore or uprate load capacity without demolition.
Commercial & Institutional Buildings
Sealing beam and column faces for fibre strengthening when a change of use or added floors increases design loads.
Seismic Retrofit
Base coat for confinement wraps on RC columns in retrofit projects across seismically active zones.
Industrial Structures
Preparing members weakened by corrosion or heavy service loads for glass or carbon fibre reinforcement.
Repair & Rehabilitation Contractors
A reliable first coat in wet lay-up FRP packages where the whole system must come from one compatible source.
Frequently asked questions
What exactly is ShaliBond GCW 340 used for?
Is this the same as ShaliWrap Primer?
Can GCW 340 strengthen a structure on its own?
Does it work with both carbon and glass fibre?
How is it applied and how long can I leave it before the next coat?
Can Space Arc both supply and apply it?
How we position STP ShaliBond GCW 340
ShaliBond GCW 340 is the primer stage of STP’s FRP strengthening range and is best specified alongside its natural system partners: ShaliBond GCW 310, the epoxy impregnation resin / saturant (formerly ShaliWrap Saturant), plus the carbon or glass fibre fabric that completes the wrap. Buying the primer, saturant and fabric from the same STP family keeps every layer chemically compatible, which is exactly what a strengthening design assumes. Where a project is written around a Fosroc FRP specification instead, the equivalent solution from our Fosroc range is the Nitowrap EP(CF) carbon-fibre system, whose own epoxy primer/saturant stages mirror GCW 340’s function. Space Arc carries both the STP and Fosroc lines, so specifiers can match whichever brand their design authority has approved rather than compromising on system integrity.
Fosroc Nitowrap EP(CF) — Choose the Fosroc Nitowrap EP(CF) carbon-fibre system when the strengthening design is written to a Fosroc specification, as its matched epoxy primer/saturant stages perform the same sealing-and-bonding role as GCW 340 within an approved single-brand system.
Related Structural Strengthening products
Source STP ShaliBond GCW 340 for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.