About MC-Bauchemie MC-RocTec HB

MC-RocTec HB from MC-Bauchemie is a purpose-built answer to a problem every repair contractor knows well: thin-coat repair mortars simply take too long and crack too readily when the section to be rebuilt runs into tens of millimetres. It is a single-component, polymer-modified cementitious mortar, but what sets it apart is the coarse aggregate graded up to 8-12 mm. That larger stone gives the mix internal restraint and dimensional stability, so the material can be placed in genuinely structural thicknesses rather than being restricted to skim depths. Just add clean water on site, mix, and place.

For engineers and consultants, the reassurance is in the classification. MC-RocTec HB is formulated to meet EN 1504-3 as a Class R3 to R4 structural repair mortar, the benchmark for load-bearing concrete restoration, and develops a 28-day compressive strength in the region of 35-45 MPa with a bond to prepared concrete exceeding 1.5 MPa under EN 1542. In practical terms it behaves as a compatible, monolithic extension of the parent concrete, restoring both cover and cross-section on the assets that carry the most load: bridges, dams, marine structures and industrial frames across Delhi NCR and the rest of India.

The technical insight

The engineering logic behind MC-RocTec HB is aggregate restraint. Every cementitious mortar shrinks as it cures and dries, and that shrinkage is what drives cracking and debonding in thick repairs. Fine-aggregate mortars have a high paste fraction, so they shrink more and must be built up in several thin passes to stay stable. By carrying stone up to 8-12 mm, MC-RocTec HB reduces the paste-to-aggregate ratio and lets the hard, dimensionally stable aggregate skeleton physically resist that movement, the same principle that lets structural concrete be cast in bulk. The result is a mortar that can be placed 40-100 mm per lift and still cure with controlled shrinkage. The polymer modification does the complementary job: it improves the wetting and adhesion at the old-concrete interface, boosts flexural and tensile behaviour, and lowers permeability so the repair resists water and chloride ingress. Together the two mechanisms turn a deep patch into a durable, load-sharing part of the structure rather than a sacrificial cosmetic layer.

Where it is used

• Reinstating spalled and delaminated concrete on bridge piers, abutments and crossheads
• Section rebuild and jacketing of columns and piers where cover and cross-section are lost
• Repair of dam faces, spillways and other mass-concrete hydraulic structures
• Restoration of retaining walls and large civil-works elements
• Structural repair of seaports, jetties and marine RC exposed to splash and tidal zones
• Large-area patch repair of industrial building frames, silos and process structures
• Deep-section reinstatement following corrosion-driven concrete breakout and rebar cleaning
• Vertical and overhead thick-build repairs where formwork-free placement is preferred

Key advantages

• Coarse 8-12 mm aggregate allows 40-100 mm build per lift, cutting the number of passes on deep repairs
• Lower paste fraction means markedly less drying shrinkage and cracking than fine-grained mortars
• Single-component and site-batched with water only, so no gauging errors and simple QA on site
• Meets EN 1504-3 Class R3 to R4 for genuine structural, load-bearing repair
• Strong bond to prepared concrete (>1.5 MPa, EN 1542) for monolithic, compatible repairs
• 28-day compressive strength of about 35-45 MPa suits medium to high-strength parent concrete
• Placeable by hand trowel or wet-spray, giving flexibility across access-restricted sites
• Backed by MC-Bauchemie’s global concrete-repair track record on infrastructure assets

Limitations & considerations

• Coarse aggregate makes it unsuitable for fine feather-edging, fairing or thin cosmetic skims – use a fine repair mortar or fairing coat for those
• Minimum practical build depth is higher than fine mortars, so it is over-specified for shallow patch repairs
• Requires mechanical breakout to sound concrete and a saturated surface-dry substrate; poor preparation compromises bond
• Water dosage must stay within roughly 3.5-4.0 litres per 25 kg bag – overwatering reduces strength and increases shrinkage
• Like all cementitious repairs it needs proper curing; hot, windy Indian site conditions demand disciplined curing to avoid plastic cracking
• Not a standalone waterproofing or anti-carbonation layer – protect with a surface coating where durability exposure demands it

Selection & best practice

Specifications

Industry use cases

How we position MC-Bauchemie MC-RocTec HB

MC-RocTec HB is the thick-section workhorse in MC-Bauchemie’s concrete-repair range – reach for it when the rebuild runs 40-100 mm deep. For finer, thinner reinstatement and feather-edging on the same job, pair it with MC-Bauchemie’s Nafufill fine-grained repair mortars (the Nafufill KM range, up to KM 250 at R4), and use an anti-carbonation or protective surface coating from the MCI / Emcephob range to safeguard the finished repair against carbonation and chloride ingress. Where a client’s specification is written around another manufacturer, Space Arc also supplies directly equivalent high-build structural repair mortars from Fosroc, Sika and Dr. Fixit, so we can match the tender rather than force a switch.

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