Sika Sikadur-30
Two-component, high-modulus thixotropic epoxy paste engineered to bond CarboDur CFRP laminates and steel plates to concrete for external structural strengthening.
What is it?
A two-component, solvent-free thixotropic structural epoxy paste adhesive used to bond carbon-fibre (CFRP) laminates and steel plates onto concrete for external reinforcement.
Where is it used?
Flexural and shear strengthening of beams, slabs, columns and bridge decks, plus seismic retrofits and load-capacity upgrades on RC and masonry structures.
Why use it?
Its high shear and creep resistance transfer load reliably between the substrate and the bonded plate, so structures gain capacity without added dead weight or heavy sections.
How is it applied?
Mixed 3:1, spread onto both the prepared concrete and the plate in a roof-ridge profile, then the plate is pressed home so a thin, void-free glue line squeezes out before cure.
About Sika Sikadur-30
Sika Sikadur-30 is the reference adhesive in the Sika structural strengthening system, developed specifically to bond Sika CarboDur CFRP plates and steel plates onto concrete, masonry and timber. It is a two-component, 100 percent solids epoxy: a resin (Part A) and a hardener (Part B) that are combined at a 3:1 ratio to form a smooth, non-sag paste. Because it is thixotropic, it holds its shape on vertical faces and soffits without slumping, which is exactly what an applicator needs when bonding a laminate to the underside of a beam or the flank of a column overhead. The cured adhesive is high-modulus and high-strength, and it develops enough bond to the concrete that failure, when tested to destruction, occurs in the concrete substrate rather than at the glue line.
For engineers and consultants, the appeal of Sikadur-30 is that it is a tolerance-friendly, well-characterised material with a long track record on bridge and building retrofits worldwide. It is moisture-tolerant before, during and after cure, tolerates the ambient temperatures typical of an Indian site (roughly +8 to +35 degrees C), and conforms to ASTM C-881 Type I, IV Grade 3, Class C and AASHTO M-235. At Space Arc Engineering we supply it as part of a complete plate-bonding package alongside CarboDur laminates and the associated primers, so the whole strengthening system is sourced and specified from one authorised channel rather than assembled from mismatched parts.
The technical insight
External plate bonding works only if the adhesive can carry the interlaminar shear generated as the strengthened member deflects and hands load off into the CFRP or steel plate. Sikadur-30 is formulated as a high-modulus epoxy so it is stiff enough to transfer that shear efficiently, yet tough enough to resist creep under permanent load, which matters because a strengthened beam carries dead load for its entire remaining life. The thixotropy is not cosmetic: it lets the applicator build a roof-ridge bead on the plate so that, when the plate is pressed onto the concrete, trapped air is expelled and a continuous, thin, void-free bond line results. A void in that bond line is a stress concentrator and a debonding initiation point, so the paste’s ability to wet out both surfaces and squeeze to a controlled thickness is central to why the system performs. Its high adhesion to both cement substrates and metals, combined with moisture tolerance, is what lets the same product bond CFRP to concrete on one job and a steel plate to concrete on the next.
Where it is used
- Bonding Sika CarboDur CFRP laminates to concrete beams and slabs for flexural strengthening
- Bonding steel plates to concrete soffits for load-capacity upgrades
- Shear strengthening of RC beams and the confinement of columns in retrofits
- Seismic retrofitting and upgrading of existing reinforced-concrete frames
- Strengthening bridge decks, girders and industrial structures against increased live loads
- Bonding external reinforcement to masonry, stone and timber substrates
- Structural bonding of precast concrete elements and connections
- Repair of structurally deficient members where added dead weight must be avoided
Key advantages
- High-modulus, high-strength bond that fails in the concrete rather than at the glue line
- Thixotropic, non-sag paste holds its profile on vertical and overhead applications
- Moisture-tolerant before, during and after cure, suiting damp Indian site conditions
- Convenient 3:1 mix ratio by weight or volume reduces on-site batching errors
- Excellent creep resistance under sustained permanent load
- Adheres to concrete, masonry, steel, stone and timber from one product
- Solvent-free, 100 percent solids formulation with negligible shrinkage
- Conforms to ASTM C-881 and AASHTO M-235, easing specification and QA sign-off
Limitations & considerations
- Not a gap-filler: the neat glue line should stay thin (nominally around 2 mm, up to about 3 mm), not used as a bulk mortar
- Application window is roughly +8 to +35 degrees C; pot life shortens sharply in Indian summer heat and larger mixes cure even faster
- Demands rigorous surface preparation (grit-blasting or grinding to a sound, laitance-free profile) or the bond is compromised
- Once mixed, the working time is limited, so batch size must be matched to how much plate can be placed before gel
- Being a rigid, high-modulus epoxy it is not intended for movement or expansion joints
- A structural adhesive to be applied by trained applicators as part of a designed strengthening scheme, not a general-purpose repair product
Selection & best practice
Prepare the concrete by grit-blasting or grinding back to a sound, clean, laitance-free surface and ensure it is dry to touch; degrease and abrade steel plates to a bright finish immediately before bonding. Batch only as much as can be placed within the pot life for the day’s temperature, and mix Part A and Part B thoroughly until a uniform grey colour with no streaks is achieved. Apply the paste to both the substrate and the plate, forming a slight roof-ridge profile on the plate so air is driven out as it is pressed home. Push the plate onto the concrete with a rubber roller until adhesive squeezes out along both edges, confirming a continuous void-free line, then strike off the excess. Protect the bond from disturbance, water and heavy load until the epoxy has developed its design strength, typically after seven days. Work within +8 to +35 degrees C and keep the glue line thin rather than treating the paste as a levelling filler.
Specifications
| Product type | Two-component, solvent-free thixotropic structural epoxy paste adhesive |
| Mixing ratio (A:B) | 3:1 by weight or by volume |
| Density (mixed A+B) | approx. 1.65 kg/l at +23 degrees C |
| Compressive strength | approx. 70-90 N/mm2 (depending on cure age and temperature) |
| Tensile strength | approx. 24-25 N/mm2 (7 days) |
| Tensile adhesion (bond) strength | >4 N/mm2 on concrete (concrete failure); high adhesion to sandblasted steel |
| Layer / glue-line thickness | thin bond line, nominally ~2 mm (max ~3 mm neat) |
| Application temperature | +8 degrees C to +35 degrees C (substrate and ambient) |
| Standards | ASTM C-881 Type I, IV Grade 3, Class C; AASHTO M-235 |
| Colour | Light grey |
Industry use cases
Bridges & Highways
Bonding CFRP laminates and steel plates to girders and decks to raise load rating for heavier traffic without rebuilding the span.
Commercial & Institutional Buildings
Flexural and shear strengthening of beams and slabs when floors are re-purposed for higher imposed loads or new openings are cut.
Seismic Retrofit
Confining columns and strengthening frames on existing RC structures to meet current seismic demand in retrofit programmes.
Industrial & Power Plants
Upgrading structural members carrying new equipment or increased dynamic loads where added dead weight and downtime must be minimised.
Heritage & Masonry Repair
Bonding external reinforcement onto masonry and stone elements to arrest distress while keeping interventions slim and reversible in appearance.
Frequently asked questions
What is Sika Sikadur-30 used for?
What is the mixing ratio and how long is the working time?
How thick can the adhesive layer be?
Can it be applied to a damp substrate?
Does it meet international standards?
Does Space Arc supply the full CarboDur strengthening system?
How we position Sika Sikadur-30
Sikadur-30 sits at the centre of Sika’s external strengthening system and is designed to be paired with Sika CarboDur CFRP laminates and, where a primer is needed, Sikadur-330 for wet-lay-up fabric systems such as SikaWrap; specify these together rather than mixing brands within one bonded assembly. Where a project standardises on Fosroc, the equivalent route is the Fosroc Nitowrap composite strengthening system, which Space Arc also supplies. For the related but distinct needs that often arise on the same retrofit, look to epoxy grouts such as Fosroc Conbextra EP for baseplates and bearings, or anchoring grouts like Fosroc Lokfix for rebar and dowel fixing, rather than using Sikadur-30 outside its plate-bonding role.
Related Structural Strengthening products
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