Fosroc Nitowrap CWS
Standard-modulus unidirectional carbon fibre fabric that adds tensile capacity to concrete beams, columns and slabs without adding weight or downtime.
What is it?
A high-strength, unidirectional carbon fibre fabric (CFRP) that is saturated with epoxy and bonded to a concrete surface to add external tensile reinforcement. CWS is the standard-modulus grade (around 230 GPa) of the Fosroc Nitowrap wrap family.
Where is it used?
Reinforced concrete beams, columns, slabs and shear walls that need extra load capacity, seismic confinement or repair after damage, corrosion or a change of use.
Why use it?
It lets you upgrade a structure in place, without demolition, added dead load or the corrosion problems of steel plate bonding. A few millimetres of fabric can carry loads that would otherwise need new steel or concrete.
How is it applied?
The concrete is prepared and primed, an epoxy saturant is applied, the CWS fabric is laid into the wet resin along the design fibre direction and rolled to remove air, then a second resin coat locks the fibres in place.
About Fosroc Nitowrap CWS
Fosroc Nitowrap CWS is the standard-modulus carbon fibre sheet within Fosroc’s Nitowrap external strengthening system. The fabric is woven so that virtually all the load-bearing fibres run in one direction, which is exactly how an engineer wants to place reinforcement: along the line of tension in a beam soffit, around the girth of a column, or across the shear plane of a web. Once the dry sheet is saturated with a structural epoxy and cured against the concrete, the fabric and resin act together as a carbon fibre reinforced polymer (CFRP) laminate that is bonded to and works compositely with the parent member.
For engineers and contractors working across Delhi NCR and the rest of India, the appeal is practical. Older buildings that need to carry heavier loads, structures downgraded by corrosion or fire, bridges facing increased traffic, and columns that must survive a design earthquake can all be brought up to specification without knocking anything down. Because the material is thin, light and non-corroding, it suits occupied buildings, tight service floors and marine or coastal exposure where a bolted steel solution would be heavy and would eventually rust. As the authorised distributor and applicator, Space Arc Engineering supplies the CWS fabric together with its matching Fosroc primer and saturant, and can execute the wrap on site to the design engineer’s drawings.
The technical insight
The mechanism is composite action through the epoxy bond line. Concrete is strong in compression but weak in tension, and it cracks long before its reinforcing steel yields. When Nitowrap CWS is bonded to the tension face, the epoxy transfers stress from the concrete into the carbon fibres through shear across the glue line. Because the fibres have a tensile strength of the order of 4,900 MPa and an elastic modulus above 230 GPa, they pick up load as soon as the concrete begins to strain, restraining crack widening and raising the member’s flexural or shear capacity. On columns the same fabric is wrapped as a continuous hoop; the confinement it provides puts the concrete core into a triaxial stress state, which increases both its compressive strength and, more importantly for seismic work, its ductility. The standard-modulus 230 GPa grade is deliberately matched to reinforced concrete: it is stiff enough to share load effectively yet retains around 2.1% ultimate elongation, so it strains with the structure rather than debonding early. Design is not by rule of thumb but to recognised CFRP codes such as ACI 440.2R or fib Bulletin 90, where the number of plies and the anchorage length are calculated for the specific member.
Where it is used
- Flexural strengthening of reinforced concrete beam soffits and slabs to carry increased loads
- Column confinement wrapping to boost axial capacity and ductility for seismic retrofit
- Shear strengthening of beams, webs and transfer structures with U-wraps or full wraps
- Restoring capacity to members weakened by corrosion, fire, impact or overloading
- Strengthening bridge girders, decks and piers facing higher traffic or load ratings
- Upgrading floors and frames before a change of building use or added storeys
- Confining and stitching cracked or repaired concrete elements after concrete repair works
- Strengthening masonry and non-rectangular sections where the fabric follows the contour
Key advantages
- Very high tensile strength (fibre >4,900 MPa) at roughly one-fifth the weight of structural steel
- Completely corrosion-free, so it suits coastal, marine and chemically aggressive exposure
- Adds only a few millimetres of thickness and negligible dead load to the structure
- Applied externally with no demolition, keeping buildings occupied and services running
- Fabric is flexible and shapes to columns, curves and irregular sections
- Fast installation shortens site programmes and reduces disruption compared with recasting
- Unidirectional weave lets the engineer align strength precisely with the line of stress
- Fully compatible as a system with Fosroc primer and epoxy saturant for a reliable bond
Limitations & considerations
- Not a fire-rated finish on its own; the epoxy softens near its glass transition (typically 60-80C), so fire-exposed wraps need intumescent coating or protective board
- Performance depends entirely on the epoxy bond, so surface preparation, priming and full saturation must be done correctly or the fabric can debond
- Requires a competent, trained applicator and engineered design to a CFRP code, not a generic waterproofing crew
- Cannot correct a member that has failed in compression or has inadequate concrete or anchorage, since the concrete substrate must still carry compression
- Being unidirectional, a single layer only adds strength along the fibre direction; multi-axis demands need additional plies in other orientations
- Epoxy application is temperature and moisture sensitive, so hot, damp or dusty site conditions must be controlled during installation
Selection & best practice
Treat the wrap as an engineered system, not a product bought off a shelf. Start with a structural design to a recognised CFRP code so the number of plies, orientation, lap and anchorage length are calculated for the actual member and load case. On site, repair and make good the concrete first, then grind the surface to expose sound aggregate, round off sharp column corners to the specified radius so the fibres are not cut, and remove all dust and laitance. Prime the prepared surface with the matching Fosroc primer, then apply the epoxy saturant and lay the CWS fabric into the wet resin along the design fibre direction, working out every air pocket with a ribbed roller before applying the sealing top coat of resin. Maintain overlaps as specified, protect the fresh wrap from rain and traffic while it cures, and where fire rating or UV exposure matters, finish with the appropriate protective coating. Keep application within the recommended temperature and humidity window and record ambient conditions.
Specifications
| Material type | Unidirectional woven carbon fibre fabric (CFRP), standard-modulus grade |
| Fibre tensile strength | >4,900 MPa (typical dry fibre) |
| Fibre elastic modulus | >230 GPa (standard-modulus grade) |
| Ultimate elongation | approx. 2.1% |
| Fibre area weight | approx. 300-450 g/m2 (grade dependent) |
| Fibre density | approx. 1.8 g/cm3 |
| Saturant / primer | Applied with matching Fosroc epoxy saturant and primer system |
| Application technique | Wet lay-up (dry or wet wrap), single or multiple plies |
| Design reference | ACI 440.2R / fib Bulletin 90 or Indian equivalent |
Industry use cases
Commercial and residential retrofit
Strengthening beams and slabs in existing buildings before adding floors, heavier services or a change of occupancy, without vacating or demolishing the structure.
Seismic upgrading
Wrapping columns and joints in older RC frames to add confinement and ductility so they meet current earthquake design requirements.
Bridges and infrastructure
Adding flexural and shear capacity to girders, decks and piers facing higher load ratings or traffic, with a lightweight non-corroding solution.
Industrial and coastal structures
Restoring capacity to members degraded by corrosion or chemical attack in plants and marine environments where steel plating would rust.
Post-repair rehabilitation
Reinforcing and confining concrete elements after crack injection or patch repair to restore or exceed the original design capacity.
Frequently asked questions
What is the difference between Nitowrap CWS and the higher grades in the range?
Can Nitowrap CWS replace steel plate bonding?
How many layers of fabric are needed?
Does the wrap need fire protection?
What surface preparation does it require?
Can Space Arc design and install the system, or only supply the material?
How we position Fosroc Nitowrap CWS
Nitowrap CWS is the standard-modulus fabric in Fosroc’s Nitowrap strengthening system and is rarely used alone. It is always installed with a matching Fosroc epoxy primer and saturant, so those companion resins should be specified together for a warranted bond. Where a design calls for a stiffer wrap, the higher and very-high modulus grades of the same Nitowrap family are the direct step-up. For strengthening that suits a rigid pre-cured laminate rather than a wet-laid fabric, Fosroc’s Nitoplate carbon fibre plate system bonded with Nitowrap 40 adhesive is the alternative approach. Since a wrap is only as good as the concrete beneath it, related concrete-repair materials such as the Renderoc mortar range and Nitofill crack-injection resins are commonly used first to reinstate the substrate. From our wider portfolio, MC-Bauchemie and Sika also offer CFRP and repair systems where a project standardises on a different brand.
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