MC-Bauchemie MC-RocTec 400
A coarse-aggregate, polymer-modified Class R4 repair mortar built for the deep, high-volume concrete losses that ordinary patch mortars cannot economically fill.
What is it?
A factory-blended, cement-based structural repair mortar carrying coarse aggregate up to 8 mm, silica fume and polymer modifiers, certified to EN 1504-3 Class R4 and supplied as a dry powder mixed with water on site.
Where is it used?
Deep-section reinstatement on bridge piers, flyover columns, dam walls, marine structures and heavy industrial foundations where large volumes of deteriorated concrete have been removed.
Why use it?
Its coarse-aggregate skeleton lets you build back 20-80 mm in a single pass with low shrinkage and strong bond, so deep repairs cure monolithically instead of cracking or delaminating.
How is it applied?
Prime the prepared, saturated substrate and steel, key an epoxy bonding coat where specified, then hand-place the mixed mortar in compacted lifts and moist-cure for at least 7 days.
About MC-Bauchemie MC-RocTec 400
MC-RocTec 400 is the answer to a problem every rehabilitation engineer knows well: what do you use when the defective concrete you have chipped out is not a shallow spall but a deep, structural pocket often 40, 60 or 80 mm back to sound substrate. Fine-grained patch mortars are formulated for thin sections, and forcing them into deep lifts invites shrinkage cracking, slumping and poor economy. MC-RocTec 400 is engineered specifically for this deep-section, large-volume situation. It is a single-component, cement-based repair mortar from MC-Bauchemie that carries a graded coarse-and-fine aggregate skeleton up to 8 mm nominal size, reinforced with silica fume and polymer modifiers, and it arrives as a factory-controlled dry powder that only needs clean water and correct mixing on site.
Because the mortar behaves more like a small-aggregate structural concrete than a thin skim, it reinstates section and load path rather than merely cosmetically covering a defect. It is classified to EN 1504-3 as a Class R4 product, the highest structural performance class in the standard, which sets the demanding thresholds for compressive strength, chloride content and thermal compatibility that a load-bearing repair on a bridge or dam must satisfy. For consultants writing repair specifications and contractors executing them across Delhi NCR and Pan-India, that R4 classification is the shorthand assurance that the rebuilt zone can carry structural duty rather than just seal a surface.
The technical insight
The reason MC-RocTec 400 can be placed in thick 20-80 mm lifts where ordinary repair mortars fail comes down to its aggregate skeleton. Every cementitious material shrinks as it hydrates and dries; the more paste and the less aggregate in the mix, the more that shrinkage translates into cracking and debonding. Fine patch mortars are paste-rich, so they are deliberately restricted to thin sections. MC-RocTec 400 instead loads the matrix with coarse aggregate up to 8 mm, and those hard particles physically restrain shrinkage the same way stone does in structural concrete, which is what keeps a deep lift dimensionally stable. The silica fume densifies and refines the paste-to-aggregate interface, lifting bond strength and cutting permeability so chlorides and carbonation struggle to reach the reinforcement. The polymer modifiers improve adhesion to the old concrete and give the fresh mortar the cohesion to stay put on vertical and deep faces. The trade-off engineers must respect is that this same coarse skeleton will segregate if the mortar is over-watered or poker-vibrated, so it is hand-compacted, not immersion-vibrated. Placed correctly over a properly prepared and bonded substrate, the repair develops a compressive strength above 45 MPa and a pull-off bond above 2.0 MPa, so the rebuilt zone acts monolithically with the parent structure.
Where it is used
- Deep-section repair of bridge piers, pier caps and abutments where cover concrete has been lost back to the reinforcement
- Reinstatement of flyover and viaduct columns suffering spalling and delamination
- Structural concrete repair of dam faces, spillways and retaining walls
- Rebuilding of heavy industrial and machine foundations where large volumes of concrete are removed
- Restoration of fire-damaged reinforced concrete elements back to full section
- Repair of marine and coastal structures exposed to chloride-laden environments
- Large-volume defect and honeycomb repair on cast-in-situ and precast members
- Section reinstatement on car parks, jetties and infrastructure where 20-80 mm build-up per pass is needed without formwork
Key advantages
- EN 1504-3 Class R4 certified, the highest structural repair class in the standard, suitable for load-bearing reinstatement
- Coarse-aggregate skeleton allows thick 20-80 mm lifts per pass, cutting the number of coats on deep repairs
- Low drying shrinkage from aggregate restraint and polymer modification, reducing the risk of map cracking in deep sections
- Compressive strength above 45 MPa at 28 days for structural-duty repairs
- High pull-off bond above 2.0 MPa when used with the specified bonding system, resisting delamination
- Silica-fume-densified matrix improves durability against carbonation, chloride ingress and thermal cycling in Indian climates
- Economical for large-volume work compared with fine mortars, since more material is placed per pass
- Single-component dry powder with controlled 3.5-4.0 litres water per 25 kg bag, giving consistent, repeatable site mixes
Limitations & considerations
- Not intended for thin or featheredge repairs; below the 20 mm minimum lift the coarse aggregate cannot be properly accommodated and a fine mortar should be used instead
- Must not be compacted with a poker/immersion vibrator, which segregates the coarse aggregate; the repair is hand-compacted
- Sensitive to over-watering; exceeding the specified water demand reduces strength and can cause bleeding and segregation
- Requires disciplined substrate preparation, saturated-surface-dry conditioning and, where specified, an epoxy bonding coat, so it is not a quick cosmetic patch
- Cement-based chemistry means adequate moist curing (minimum 7 days, extended in hot weather) is essential, and hot-weather placing needs planning
- Pot life of roughly 30-45 minutes at 25 degrees C shortens in Indian summer heat, limiting batch size and open time
Selection & best practice
Success with MC-RocTec 400 is decided before any mortar is mixed. Break out all unsound concrete back to a sound, roughened substrate, expose corroded reinforcement fully around its circumference, and clean the steel to bright metal before applying the specified anti-corrosion primer. Bring the substrate to a saturated-surface-dry condition, then apply the epoxy bonding coat where the specification calls for it and place the mortar while that coat is still tacky. Mix each 25 kg bag with 3.5-4.0 litres of clean water in a forced-action mixer to a uniform, cohesive consistency, never adding extra water to improve workability. Place and hand-compact in lifts within the 20-80 mm range, working the mortar firmly against the substrate and reinforcement to eliminate voids, and finish before initial set. Cure immediately and continuously by moist hessian or a curing membrane for at least 7 days, extending curing in hot, dry or windy conditions. Always confirm layer limits, primer and curing details against the current MC-Bauchemie technical data sheet for the batch supplied.
Specifications
| Product type | Single-component, polymer-modified coarse-aggregate cementitious repair mortar |
| EN 1504-3 classification | Class R4 (structural) |
| Maximum aggregate size | 8 mm nominal |
| Compressive strength (28 days) | > 45 MPa |
| Bond strength (pull-off) | > 2.0 MPa |
| Layer thickness per pass | 20 mm (min) to 80 mm (max) |
| Water demand | 3.5-4.0 litres per 25 kg bag |
| Pot life (approx.) | 30-45 minutes at 25 degrees C |
| Pack size | 25 kg multi-wall paper bags |
Industry use cases
Bridges & Highways
Rebuilding spalled, delaminated pier caps, abutments and flyover columns back to full section where deep cover concrete has been lost around the reinforcement.
Dams & Water Retaining
Structural repair of dam faces, spillways and retaining walls that need durable, high-strength reinstatement in continuously wet, aggressive service.
Marine & Coastal
Restoring chloride-damaged jetties, sea walls and coastal RCC where a dense, low-permeability R4 mortar resists further salt ingress.
Industrial & Power
Reinstating heavy machine foundations, plinths and fire-damaged structural members where large concrete volumes must be replaced to carry load again.
Infrastructure Rehabilitation
Large-volume defect, honeycomb and deep-pocket repairs on ageing civil structures where economical thick-lift placement without formwork is the priority.
Frequently asked questions
What makes MC-RocTec 400 different from a normal repair mortar?
What thickness can I apply in one pass?
Is it strong enough for structural, load-bearing repairs?
Why can’t I vibrate it with a poker vibrator?
How much water and how big is a bag?
Do I need a bonding agent and primer?
How we position MC-Bauchemie MC-RocTec 400
MC-RocTec 400 is the deep-section, coarse-aggregate workhorse of the MC-Bauchemie concrete-repair line. Where the loss is shallower or a finer finish is needed, pair it with a fine-grained MC-Bauchemie R3/R4 repair mortar from the same Nafufill family for the top layers, and specify an MC-Bauchemie anti-corrosion primer and epoxy bonding coat as the interface system. Space Arc also supplies genuine equivalents across other brands we distribute: Fosroc’s Renderoc range for hand-applied and flowing micro-concrete repairs, and Sika’s MonoTop and SikaGrout systems for R4 replacement and deep pours. For consultants who prefer a Fosroc-specified repair build-up, our team can map an equivalent MC-RocTec 400 solution to the corresponding Fosroc grade so the performance class stays consistent across the specification.
Fosroc Renderoc HB40 — A specifier standardising on a Fosroc repair build-up may prefer Renderoc HB40 for hand-applied vertical and overhead reinstatement up to 40 mm per pass, though for the deepest 60-80 mm large-volume sections MC-RocTec 400 or a flowing Fosroc micro-concrete is better suited.
Related Concrete Repair products
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