Sika Sikadur-31 IN
A two-part, moisture-tolerant thixotropic epoxy that structurally bonds concrete, steel, stone and more, and doubles as a fast-setting repair paste on vertical and overhead surfaces.
What is it?
A two-component, solvent-free thixotropic structural epoxy adhesive and repair paste based on epoxy resins and special fillers, supplied as a grey paste in a 2:1 (A:B by weight) system.
Where is it used?
Bridge repairs, precast erection, structural steel bonding, edge and spall reinstatement, and crack or joint sealing on dry or matt-damp concrete substrates.
Why use it?
It grips tenaciously to damp surfaces without a separate primer, holds on vertical and overhead work without sagging, and cures without shrinkage to give a bond stronger than the parent concrete.
How is it applied?
Mix the pre-weighed A and B components to a uniform grey, then trowel or spatula-apply in layers up to 30 mm onto a sound, prepared substrate within the pot life.
About Sika Sikadur-31 IN
Sikadur-31 IN is Sika’s workhorse structural epoxy for situations where a cementitious mortar simply will not hold. It arrives as a pre-batched two-part kit: a resin base and a hardener that combine at a 2:1 ratio by weight into a stiff, grey, non-sag paste. Because it is thixotropic, it stays exactly where the applicator places it, which is what makes it usable on vertical faces, soffits and overhead pours where a flowable grout would run off. It is solvent-free and cures without shrinkage, so bonded joints and reinstated edges keep their dimension and do not crack away from the substrate as they harden.
What sets this product apart on Indian sites is its tolerance for moisture. Concrete in the field is rarely bone-dry, and Sikadur-31 IN is formulated to bond to matt-damp as well as dry surfaces without a separate primer step, provided the substrate is sound and free of standing water. That single property saves a curing wait on repair programmes and makes it dependable in monsoon-season and below-grade work. Contractors reach for it in two roles at once: as a genuine structural adhesive for bonding dissimilar materials, and as a fast, high-strength repair mortar for filling voids, rebuilding corners and sealing cracks.
The technical insight
The performance comes from the epoxy chemistry itself. When the amine hardener (Part B) reacts with the epoxy resin (Part A), it forms a dense, three-dimensional cross-linked network rather than the loose hydrated matrix of a cement mortar. That network is what delivers a tensile adhesion above 10 N/mm², high enough that a pull-off test fails inside the concrete rather than at the glue line. The special fillers give the mix its thixotropy: at rest the paste is stiff and holds its shape, but under the shear of a trowel it flows enough to wet out the surface and key into the substrate’s micro-texture. Curing is a chemical reaction, not a drying process, so the material sets even on a damp surface and shrinks negligibly, unlike cement systems that lose water and pull back. The trade-off, inherent to all epoxies, is temperature sensitivity: warmer conditions accelerate the reaction and shorten working time, which is why pot life is quoted against a specific temperature.
Where it is used
- Structural bonding of precast concrete units, kerbs and segmental elements during erection
- Fixing steel plates, sections and fixtures to concrete for strengthening work
- Reinstating spalled concrete, broken corners and damaged edges on beams, columns and slabs
- Filling blowholes, voids and honeycombing on formed and cast concrete faces
- Sealing and filling non-moving cracks and static joints in concrete and masonry
- Bonding hard natural stone, brick, block and ceramic to concrete or steel substrates
- Grout-check and formwork sealing before injection or pressure grouting operations
- Adhesive fixing of timber, composite and metal components in repair and retrofit projects
Key advantages
- Bonds to matt-damp as well as dry substrates, so repairs proceed without a drying wait
- Thixotropic non-sag consistency stays put on vertical and overhead surfaces
- Solvent-free and cures without shrinkage, keeping joints and edges dimensionally stable
- Develops a bond to concrete stronger than the parent material (concrete failure in pull-off)
- Pre-batched 2:1 kit removes site weighing errors and gives repeatable mix quality
- No separate primer required, cutting one step and one consumable from the process
- High compressive strength around 60 N/mm² suits load-bearing repair and bonding roles
- Works across a wide +10 C to +40 C application window suited to most Indian site conditions
Limitations & considerations
- Working time is limited; pot life is roughly 40 minutes for a 100 g mix at +30 C and falls as temperature rises, so only mix what can be placed in time
- Maximum layer thickness is 30 mm per application, so deep reinstatement needs building up in passes
- Not intended for moving or dynamic cracks and joints that require a flexible sealant
- Substrate must be sound, clean and at least 3 C above the dew point, with no standing water or ice
- Epoxy cost per kilogram is higher than cementitious mortars, so it is specified where its bond and speed are genuinely needed
- Colour is a fixed grey paste and is not intended as a finished, colour-matched surface
Selection & best practice
Prepare the substrate mechanically to a sound, clean, laitance-free profile and remove all dust, oil, grease and loose particles; concrete should be at least 28 days old. Confirm the surface is dry or only matt-damp, with no free water, and that substrate, ambient and product temperatures all sit between +10 C and +40 C, with the surface at least 3 C above dew point. Mix the full Part A into Part B and blend with a slow-speed drill and paddle until the paste is a uniform, streak-free grey, scraping the sides and base of the container. Only batch what your team can apply within the pot life, remembering that heat shortens it sharply. Work the paste firmly onto the prepared surface with a trowel or spatula to wet it out, then build to the required profile in layers not exceeding 30 mm. Protect fresh work from rain and running water until it has cured, and clean tools with solvent immediately, as cured epoxy can only be removed mechanically.
Specifications
| Chemical base | Two-component epoxy resin with special fillers |
| Consistency / colour | Thixotropic paste, grey |
| Mixing ratio (A:B) | 2 : 1 by weight |
| Coverage | Approx. 2.0 kg/m² per mm of layer thickness |
| Maximum layer thickness | 30 mm per application |
| Pot life | At least 40 min for a 100 g mix at +30 C |
| Compressive strength | Approx. 60 N/mm² |
| Tensile adhesion to concrete | >10 N/mm² (failure in the concrete) |
| Application temperature | +10 C to +40 C (substrate, ambient and product) |
| Pack sizes | 3 kg, 6 kg and 30 kg |
Industry use cases
Bridges & Infrastructure
Bonding precast segments and steel strengthening plates, and reinstating spalled kerbs and parapets, often on damp deck surfaces where a fast structural grip is critical.
Precast & Prefabrication
Erecting and jointing precast units, fixing inserts and rebuilding damaged edges of panels before installation, with a non-sag paste that holds on vertical faces.
Industrial Structures
Anchoring steel fixtures, base plates and machine supports to concrete, and repairing impact-damaged corners of columns and plinths in plants and warehouses.
Building Repair & Retrofit
Filling honeycombing and blowholes, sealing static cracks and bonding stone or masonry back to structural concrete during façade and structural rehabilitation.
Water-Retaining & Below-Grade
Reinstating edges and filling voids on damp basement, tank and retaining-wall concrete, where the moisture tolerance of the epoxy avoids waiting for surfaces to dry.
Frequently asked questions
Can Sikadur-31 IN be applied to a damp concrete surface?
What is the mixing ratio and how much working time do I get?
How thick a repair can I build in one pass?
How strong is the bond compared with the concrete itself?
Is it suitable for sealing cracks and joints that move?
What pack sizes are available and how much will I need?
How we position Sika Sikadur-31 IN
Within the Sika range, Sikadur-31 IN is the general-purpose structural bonding and repair paste; where a specifier needs a flowable, higher-strength epoxy for pressure-injection or bonding of external reinforcement, the Sikadur-30 and Sikadur crack-injection resins are the natural companions, and Sika MonoTop cementitious mortars suit larger-volume, cost-sensitive reprofiling. For teams standardised on other brands we carry, Dr. Fixit and MC-Bauchemie offer comparable epoxy bonding systems, while cementitious repair is well covered by our UltraTech and Fosroc mortar ranges. Talk to us if you are matching an existing specification and we will cross-reference the right equivalent.
Fosroc Nitobond EP — Where the job is primarily a bond coat between prepared concrete and a fresh repair mortar or overlay rather than a gap-filling structural paste, a specifier standardised on Fosroc may prefer Nitobond EP, a two-component epoxy bonding agent for that priming role.
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