Sika Sikadur-31 CF Normal
A moisture-tolerant, non-sag two-component epoxy adhesive and repair mortar for structural bonding, anchoring and rigid crack sealing on concrete, steel, stone and masonry.
What is it?
A two-component thixotropic epoxy adhesive and filling mortar (resin plus hardener) that cures to a high-strength, shrinkage-free rigid bond on most construction substrates.
Where is it used?
Bonding precast and cast-in-situ concrete elements, fixing steel bearing plates and profiles, anchoring dowels, sealing static cracks, and rebuilding damaged edges and corners in repair and rehabilitation work.
Why use it?
It develops a bond to concrete stronger than the parent substrate (failure occurs in the concrete, not the glue), needs no primer, tolerates matt-damp surfaces, and stays put on vertical and overhead faces.
How is it applied?
Mix Part A and Part B 2:1 by weight for about 3 minutes with a slow-speed drill, then trowel or spatula onto a clean, prepared, dry-to-matt-damp surface within the pot life.
About Sika Sikadur-31 CF Normal
Sikadur-31 CF Normal is one of Sika’s most widely specified structural epoxy adhesives, and it earns that place by doing two jobs at once: it is both a high-strength glue and a repair mortar. Supplied as a pre-batched two-part system, Part A is a white epoxy resin and Part B a dark grey hardener; the contrasting colours are deliberate, letting the applicator confirm a uniform grey mix has been reached before the material goes down. Once mixed it behaves as a thixotropic paste, thick and non-sag at rest yet workable under the trowel, which is why it holds its shape up to roughly 15 mm on a vertical or overhead surface without slumping.
For engineers and contractors across Delhi NCR and the rest of India, its appeal is dependability under site conditions. It bonds to concrete, hard natural stone, ceramics, fibre cement, brick and masonry, steel, aluminium, wood, cured epoxy and glass, tolerates a matt-damp substrate where many epoxies demand bone-dry conditions, and cures without shrinkage so it will not pull away from the bond line as it hardens. Space Arc Engineering supplies Sikadur-31 CF Normal as an authorised distributor with technical back-up on substrate preparation, pot-life management in the summer heat, and selection against neighbouring Sika and other-brand products where a different grade fits the job better.
The technical insight
The performance comes from a filled bisphenol-based epoxy resin cross-linked by an amine hardener. When A and B react, they polymerise into a dense, rigid thermoset with no solvent to flash off and effectively no shrinkage, so the cured mortar keeps intimate, gap-free contact with both faces of the bond. That contact is what lets the adhesion exceed the tensile capacity of the concrete itself: in pull-off testing the failure plane runs through the concrete substrate rather than the adhesive interface, which is the outcome a repair specifier actually wants. The special fillers give the paste its thixotropy, so it resists sag on soffits and vertical faces while remaining trowelable, and they also raise abrasion resistance and impermeability to water and vapour. Cure is temperature-driven, so pot life and strength gain track ambient conditions closely, and the resin is formulated for low creep under sustained load, though as with all polymers the long-term design load must be held well below the short-term failure load.
Where it is used
- Bonding new-to-old concrete and joining precast concrete elements at structural interfaces
- Bedding and levelling steel bearing plates, base plates and machine feet on concrete
- Anchoring dowel bars, starter bars and bolts into pre-drilled holes
- Bonding steel plates and profiles to concrete for section strengthening (support required while curing)
- Rigid sealing and filling of static, non-moving cracks in concrete
- Rebuilding damaged arrises, corners, edges and honeycombed pockets as a repair mortar
- Structural bonding of hard natural stone, brick, masonry and ceramic to concrete
- Fixing fibre-cement, timber, epoxy and glass components to structural substrates
Key advantages
- Bond to concrete exceeds the substrate strength, giving 100% concrete failure in pull-off tests
- Moisture-tolerant: bonds to dry or matt-damp concrete, not just perfectly dry surfaces
- Thixotropic and non-sag up to about 15 mm on vertical and overhead faces
- Cures without shrinkage, keeping a gap-free bond line
- No primer required, which cuts one step from the site programme
- Contrasting A and B colours confirm a correct, uniform mix before application
- High early and ultimate mechanical strength for fast load transfer
- Impermeable to liquids and water vapour with good chemical and abrasion resistance
Limitations & considerations
- Rigid when cured, so it must only be used on static, non-moving cracks and joints, never on live or dynamic joints
- Working window is short in Indian summers; pot life drops to roughly 35 minutes at +30 C, so batches must be planned
- Designed for use between +10 C and +30 C; outside this band cure behaviour and workability change
- Layer thickness is capped at 30 mm per pass and needs successive layers or formwork for deeper builds
- Must not be applied over standing water, ice, laitance, oil or old coatings; surface preparation is non-negotiable
- Long-term sustained design load must stay below about 20-25% of the failure load to allow for creep, and a structural engineer must sign off load calculations
Selection & best practice
Concrete must be at least 28 days old, sound, and prepared mechanically by grit blasting, grinding or scabbling to an open, laitance-free texture; steel is de-rusted to Sa 2.5 with a bright finish. Remove all dust by vacuum before you open the tins. The substrate may be dry or matt-damp but must carry no standing water, and its temperature should stay at least 3 C above dew point to avoid condensation. Mix Part A and B at 2:1 by weight for a full 3 minutes on a slow drill (max 300 rpm), then decant and stir once more for a minute to keep air out, and mix only what you can place within the pot life. Brush the first pass firmly into the substrate for maximum grip, apply adhesive to both faces when bonding, and prop or clamp heavy or vertical components until fully hardened. In peak summer, chill the components (not below +5 C) or split the mix into smaller portions to buy working time. Clean tools with Sika Colma Cleaner immediately; cured material only comes off mechanically.
Specifications
| Composition | Two-component thixotropic epoxy (resin + hardener) |
| Mixing ratio (A:B) | 2 : 1 by weight or volume |
| Density (A+B mixed) | 1.90 +/- 0.1 kg/l at +23 C |
| Compressive strength | ~65 N/mm2 (7 days at +23 C, EN 196) |
| Tensile strength in flexure | ~35 N/mm2 (7 days at +23 C) |
| Tensile adhesion to concrete | >4 N/mm2, 100% concrete failure (EN 1542) |
| Pot life | ~55 min at +23 C, ~35 min at +30 C, ~145 min at +10 C |
| Layer thickness / consumption | 2-30 mm; ~1.9 kg/m2 per mm of thickness |
| Standard / packaging | EN 1504-4, CE-marked; 6 kg and 30 kg pre-batched units; 24-month shelf life |
Industry use cases
Bridges & infrastructure
Bonding precast segments, fixing bearing plates and anchoring dowels during rehabilitation of decks, piers and abutments.
Industrial & commercial buildings
Steel plate bonding for beam and column strengthening, and re-fixing base plates for machinery and structural steel.
Precast & prefab
Structural jointing of precast panels, staircases and elements where a rigid, high-strength bond line is required.
Repair & rehabilitation contractors
Rebuilding spalled edges, corners and honeycombed pockets, and rigidly sealing static cracks in ageing RCC.
Heritage & stone masonry
Bonding hard natural stone, brick and masonry back to structural substrates during conservation and restoration.
Frequently asked questions
What is the mixing ratio of Sikadur-31 CF Normal?
Can it be used on damp concrete?
How much do I need per square metre?
What is the pot life on an Indian summer site?
Is it suitable for moving or expansion joints?
What maximum thickness can I apply in one pass?
How we position Sika Sikadur-31 CF Normal
Sikadur-31 CF Normal is the go-to grade when you need a general-purpose structural epoxy that both bonds and rebuilds. Within the same Sika family, reach for Sikadur-31 IN when a slightly higher application ceiling of +40 C suits the site, step up to Sikadur-30 for carbon-plate (CFRP) bonding in structural strengthening, choose a Sikadur injection resin such as Sikadur-52 for pressure-injecting fine cracks rather than surface-sealing them, and use Sika AnchorFix cartridge systems for high-volume chemical anchoring of rebar and bolts. Where the job calls for a flowable cementitious grout under base plates instead of an epoxy paste, SikaGrout is the right neighbour. Across our other brands, Fosroc, Dr. Fixit, MC-Bauchemie and Master Builders Solutions offer parallel epoxy repair and anchoring lines, so we can match availability, budget and specification. Talk to Space Arc if you are unsure which grade the drawings actually require.
Fosroc Nitomortar S — A specifier working to a Fosroc schedule can substitute this solvent-free structural epoxy repair mortar where the priority is deep-profile reinstatement and chemical resistance rather than thin-bed structural bonding.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.