Fosroc Renderoc HS Xtra
A fibre-reinforced, shrinkage-controlled cementitious mortar built for high-load structural repairs that have to hold first time.
What is it?
A single-component, fibre-reinforced cementitious repair mortar that mixes with water alone and is engineered with Dimensional Stability Technology to control drying shrinkage.
Where is it used?
Vertical and overhead concrete repairs on columns, beams, soffits, bridge decks, marine structures and masonry where load-bearing capacity and cover restoration matter.
Why use it?
It combines high compressive strength (up to 70 N/mm2) with controlled shrinkage and very low permeability, so patches stay bonded and crack-free rather than debonding over time.
How is it applied?
Mixed with 4.5 litres of clean water per 25 kg bag, then hand-applied by trowel in 10-100 mm lifts or spray-applied with suitable equipment over a prepared, saturated substrate.
About Fosroc Renderoc HS Xtra
Renderoc HS Xtra is Fosroc’s high-specification member of the Renderoc repair family, aimed at situations where a patch cannot be allowed to shrink, crack or lose bond. It arrives as a factory-blended dry powder reinforced with fibres, and on site it needs nothing more than clean water and a forced-action mixer. That single-component format matters on real jobs: there is no second liquid component to meter, no risk of a site hand getting the ratio wrong, and every bag performs the way the lab said it would. Once mixed it produces a cohesive, thixotropic mortar that stays put on vertical faces and overhead soffits without slumping, which is exactly where most structural repair work happens.
What sets this grade apart from ordinary patch mortars is Fosroc’s Dimensional Stability Technology, which governs how fast the material gives up water as it cures. Uncontrolled drying shrinkage is the usual reason a repair looks perfect for a month and then hairlines around the edges or lifts at the interface. By holding drying shrinkage below 500 microstrain at 28 days and keeping permeability under 5 mm, Renderoc HS Xtra ages in step with the parent concrete instead of fighting it. For engineers and consultants specifying rehabilitation of RCC structures across Delhi NCR and pan-India, that translates into repairs that are durable, chloride-free and genuinely compatible with the host substrate rather than a cosmetic fix.
The technical insight
The performance story is really about water management. Cementitious repair mortars fail at the bond line because they lose moisture faster than the substrate, contract, and pull away or crack. Renderoc HS Xtra is formulated so the rate of drying shrinkage is controlled rather than left to ambient conditions, which is what keeps drying shrinkage under about 300 microstrain at 7 days and under 500 microstrain at 28 days. The fibre reinforcement bridges the micro-tensile stresses that develop during this window, so the mortar resists the plastic and early-age cracking that fibres are best at arresting. Layered on top of that is a dense, low-permeability matrix (below 5 mm to DIN 1048 Part 5, water absorption under 2%) that both delivers the high strengths and slows the ingress of chlorides and moisture that drive further corrosion. The net effect is a repair whose modulus, thermal movement and durability sit close to the host concrete, so stress is not concentrated at the interface. Getting there depends on discipline: the properties are calibrated to a fixed water addition, and adding more water to make the mortar easier to place directly undoes the shrinkage control and the strength.
Where it is used
- Restoring lost concrete cover (‘covercrete’) on carbonation- or chloride-damaged columns, beams and slabs
- Vertical and overhead structural repairs where the mortar must resist slump without formwork
- Reinstating spalled and honeycombed concrete around exposed, cleaned and primed reinforcement
- Filling voids and defects greater than 10 mm deep in load-bearing members
- Rehabilitation of bridge decks, piers, soffits and other infrastructure elements
- Repairs to marine and coastal structures such as seawalls and quays (with an epoxy bonding barrier)
- Patch repairs to precast units, masonry and general concrete before protective coating
- Larger-scale hand or spray repairs on facades and industrial structures where access is difficult
Key advantages
- Single-component: add only clean water, removing on-site batching and ratio errors
- High strength development, reaching roughly 60 N/mm2 at 7 days and over 70 N/mm2 at 28 days
- Dimensional Stability Technology controls drying shrinkage, reducing edge cracking and debonding
- Fibre reinforcement resists early-age and plastic cracking during cure
- Low permeability (<5 mm) and water absorption below 2% for long-term durability
- Chloride-free and non-flammable, safe alongside embedded steel reinforcement
- Thixotropic build allows 10-100 mm lifts on vertical and overhead surfaces without formwork
- Can be hand-applied or spray-applied, suiting both small patches and large-area rehabilitation
Limitations & considerations
- Do not use when ambient temperature is below 5 C and falling
- Must not be part-mixed or part-bags used, as this compromises consistency and performance
- No additional water beyond the specified 4.5 litres per 25 kg bag, or shrinkage control and strength are lost
- Must not be exposed to running water during application or before final set
- Single-application thickness is capped (up to 50 mm overhead, 75 mm vertical, 100 mm in horizontal pockets); deeper or larger areas need a mass-fill product
- Contains reactive cement powders that release alkalis, requiring gloves, eye and respiratory protection
Selection & best practice
Preparation drives the result. Break out to sound concrete, expose and clean the reinforcement to remove all corrosion, and apply an appropriate anti-corrosion primer to the steel before patching. Saturate the prepared substrate to a saturated-surface-dry condition so the parent concrete does not draw water out of the fresh mortar. Mix a full 25 kg bag with exactly 4.5 litres of clean water in a forced-action mixer until uniform and lump-free; never add water to improve workability. Apply firmly by trowel, working the mortar well into the substrate and around the reinforcement, respecting the single-lift limits (10 mm minimum, up to 50 mm overhead, 75 mm vertical, 100 mm in horizontal pockets) and building up in layers once each reaches initial set. Where a bond barrier, extended working time, or a permanently wet or damp substrate is involved (seawalls, quays), prime with Nitobond EP epoxy bonding agent first. If a repair exceeds about 2.5 m2, switch to a mass-fill approach with a spray mortar or microconcrete. Finish and then cure properly to protect against premature moisture loss.
Specifications
| Product type | Single-component, fibre-reinforced, shrinkage-controlled cementitious repair mortar |
| Compressive strength | ~60 N/mm2 at 7 days; >70 N/mm2 at 28 days |
| Flexural strength | >13 N/mm2 at 28 days (BS 6319 / BS EN 196-1) |
| Tensile strength | >6 N/mm2 at 28 days (BS 6319 Part 7) |
| Drying shrinkage | <300 microstrain at 7 days; <500 microstrain at 28 days (ASTM C157-93) |
| Permeability / water absorption | <5 mm (DIN 1048 Part 5); <2% (BS 1881 Part 121) |
| Water addition | 4.5 litres of clean water per 25 kg bag |
| Application thickness (single lift) | 10 mm min; up to 50 mm overhead, 75 mm vertical, 100 mm horizontal pockets |
| Yield / pack | ~13.4 litres per 25 kg bag; supplied in 25 kg bags |
Industry use cases
Infrastructure & bridges
Reinstating spalled soffits, piers and deck edges where high strength and shrinkage control keep repairs bonded under live traffic loads and weathering.
Commercial & residential RCC
Repairing carbonation-damaged columns and beams and restoring cover to corroding reinforcement in ageing buildings across Delhi NCR.
Marine & water-retaining structures
Patching seawalls, quays and tanks in permanently wet or damp zones, used with a Nitobond EP epoxy bond barrier for reliable adhesion.
Industrial plants & precast
Overhead and vertical repairs to load-bearing frames, precast units and structures where formwork is impractical and downtime must be minimised.
Facade & heritage masonry
Rebuilding honeycombed or defective concrete and masonry ahead of a protective coating, with fibre reinforcement limiting early-age cracking.
Frequently asked questions
How much water do I add per bag of Renderoc HS Xtra?
What thickness can I apply in a single pass?
Do I need a bonding agent or primer?
How is it different from standard Renderoc HS?
Is it safe next to reinforcement steel?
Can it be sprayed for larger areas?
How we position Fosroc Renderoc HS Xtra
Renderoc HS Xtra sits at the premium, high-durability end of Fosroc’s Renderoc concrete-repair range that Space Arc supplies. Where a repair is routine and the extra shrinkage control is not critical, standard Renderoc HS is the more economical high-strength choice; for very large or spray-only sections beyond about 2.5 m2, Renderoc SP (spray-applied) or a Renderoc LA-type microconcrete is the right mass-fill partner. Nearly every Renderoc HS Xtra job pairs with two supporting Fosroc products from our catalogue: Nitobond EP epoxy bonding agent where a bond barrier or wet substrate demands it, and a reinforcement primer to protect exposed steel before patching. Space Arc also stocks equivalent repair mortars from Sika, MC-Bauchemie and Dr. Fixit, so specifiers who are standardised on another system can be matched to a like-for-like grade rather than being pushed to switch.
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