Fosroc Renderoc SPXtra
Shrinkage-controlled, polymer-modified cementitious repair mortar engineered for wet/dry spray and hand application on high-volume vertical and overhead concrete repairs.
What is it?
A ready-to-use, single-component, polymer-modified cementitious repair mortar that you mix with clean water on site. It is designed primarily for spray application (wet or dry process) but can also be hand-applied, and uses Fosroc’s Dimensional Stability Technology to control drying shrinkage.
Where is it used?
Large-area and high-build structural concrete repairs, particularly vertical and overhead surfaces such as bridge soffits, jetty and quay structures, parking structures, water-retaining structures, and fire-damaged concrete across infrastructure and industrial projects in India.
Why use it?
It allows fast, high-volume repairs in fewer passes with very low rebound, controls shrinkage to avoid cracking and debonding, and offers low permeability for durable, long-life repairs that behave close to the parent concrete.
How is it applied?
Mixed at 4.25-4.5 litres of water per 25 kg bag (water:powder ratio around 0.18), then applied by wet or dry gunite/shotcrete spray equipment, or trowel-applied by hand to a minimum 10 mm thickness, after proper substrate preparation and (where needed) a Nitobond EP bond coat.
About Fosroc Renderoc SPXtra
Fosroc Renderoc SPXtra is a high-performance concrete repair mortar that sits in the upper tier of the Renderoc range, aimed specifically at jobs where large volumes of material must be placed quickly and reliably on vertical and overhead surfaces. It arrives as a factory-blended dry powder of selected cements, graded aggregates and a polymer dispersion that only needs the addition of clean water on site. Once mixed, it produces a cohesive, sag-resistant mortar that can be pumped and sprayed through wet- or dry-process gunite equipment, or simply trowelled by hand for smaller sections and detailing.
The defining feature of the product is Fosroc’s Dimensional Stability Technology. Drying shrinkage is the single most common cause of repair failure: as a conventional mortar dries it contracts, and because it is bonded to a stable concrete substrate, that contraction shows up as cracking, curling and eventual debonding. Renderoc SPXtra is formulated so that the rate and magnitude of drying shrinkage are tightly controlled, recording less than 300 microstrain at 7 days and less than 500 microstrain at 28 days to ASTM C 157-93. The practical result is that a repair placed correctly stays dimensionally stable, so the bond with the parent concrete is preserved and shrinkage-induced cracking is largely eliminated.
For Indian conditions, this matters a great deal. Coastal and high-humidity zones from Mumbai to Chennai, heavily carbonated urban structures across Delhi NCR, and bridge and flyover stock under continuous traffic loading all demand repairs that are durable, low-permeability and fast to execute with minimum disruption. Renderoc SPXtra answers this with extremely low permeability (less than 8 mm to DIN 1048 Part 5) and an Initial Surface Absorption of 0.04 percent, which slows the re-ingress of water, chlorides and carbon dioxide that drive reinforcement corrosion. Its high build capability, up to 150 mm overhead and 200 mm on vertical faces in a single spray application, means deep section loss can be reinstated in one operation rather than many thin lifts.
Space Arc Engineering supplies Renderoc SPXtra as an authorised Fosroc distributor across Delhi NCR and Pan-India, alongside the associated primers, bonding agents and protective coatings needed to build a complete, warrantable repair system.
The technical insight
The engineering value of Renderoc SPXtra is best understood through the relationship between shrinkage, bond and permeability rather than headline strength alone. At a water:powder ratio of approximately 0.18 the mortar develops greater than 50 N/mm2 compressive strength at 28 days when hand-applied (BS 1881 Pt.116) and greater than 60 N/mm2 when spray-applied, with flexural strength greater than 10 N/mm2 (BS 6319 Pt.3) and tensile strength greater than 5 N/mm2 (BS 6319 Pt.7). These figures sit comfortably above typical structural-grade host concrete, but the more important property is restrained shrinkage. Because the mortar shrinks so little, the tensile stress generated at the bond line stays well below the bond strength, which is the real failure mechanism designers worry about. Low permeability (less than 8 mm, DIN 1048 Pt.5) and very low surface absorption then protect the embedded steel by limiting moisture and chloride transport. One further design lever is electrical resistivity: Renderoc SPXtra can serve as a cathodic protection overlay where the required resistivity is below 20,000 Ohm-cm, allowing it to be integrated with impressed-current or galvanic CP systems on chloride-contaminated structures. Where a damp substrate, a moisture barrier or extended working time is required, a Nitobond EP epoxy bond coat is specified at the interface.
Where it is used
- Spray-applied (wet or dry process) reinstatement of large-area concrete loss on vertical and overhead surfaces
- High-build single-layer repairs up to 150 mm overhead and 200 mm on vertical sections
- Mass infill to extensive deteriorated zones on bridges, soffits and structures
- Reprofiling of irregular and damaged concrete profiles
- Restoration of fire-damaged concrete where heat has spalled cover and reduced section
- Fast-track repair programmes requiring rapid placement of high volumes with low rebound
- Cathodic protection overlay where required resistivity is below 20,000 Ohm-cm
- Repairs to marine and water-contact structures such as seawalls, jetties and quays (with a Nitobond EP bond coat on damp substrates)
Key advantages
- Dimensional Stability Technology controls drying shrinkage (<300 microstrain at 7 days, <500 at 28 days), preventing cracking and debonding
- Suited to both spray (wet/dry gunite) and hand application from a single product
- Very low rebound during spraying, reducing material wastage and cost
- High build in one pass (up to 150 mm overhead, 200 mm vertical) speeds up high-volume repairs
- Extremely low permeability (<8 mm DIN 1048 Pt.5) and low surface absorption (0.04% ISAT) for durable, corrosion-resisting repairs
- High structural strengths: >50 N/mm2 (hand) / >60 N/mm2 (spray) compressive at 28 days
- Single-component, factory-blended powder needing only clean water, minimising site batching error
- Non-flammable, presenting no fire hazard during storage or use
- Can function as a cathodic protection overlay below 20,000 Ohm-cm resistivity
Limitations & considerations
- Must not be applied when the ambient temperature is below 5C and falling
- Part bags must never be used and no extra water added beyond 4.25-4.5 L/25 kg, or the Fosroc product guarantee is invalidated
- Should not be exposed to running water during application or before final set
- Optimum spray application requires suitable wet or dry gunite/shotcrete equipment and a trained operator
- On damp substrates, seawalls or quays a Nitobond EP epoxy bond coat is required for adequate bond
- Shelf life of 12 months can fall to as little as 4 months under high temperature and/or humidity if poorly stored
- Minimum applied thickness of 10 mm means it is not intended for thin skim or feather-edge work
- Like all cementitious products it requires correct curing to achieve stated performance
Selection & best practice
Begin with thorough substrate preparation: break out all loose, delaminated and carbonated concrete back to sound material, expose corroded reinforcement fully around its circumference, and clean the steel to bright metal before applying a Fosroc Nitozinc or Nitoprime reinforcement primer as specified. Saturate the prepared substrate to a saturated-surface-dry condition; where the substrate will remain damp (seawalls, quays, tidal zones) or where enhanced bond is needed, apply a Nitobond EP epoxy bond coat and place the mortar wet-on-wet. Mix only full 25 kg bags with 4.25 to 4.5 litres of clean water using a forced-action mixer, never adding extra water. Apply by wet or dry spray for large areas, respecting the maximum build limits (150 mm overhead, 200 mm vertical) and a 10 mm minimum thickness; trowel-finish as required. Cure the repair properly with Concure curing membrane or wet hessian to protect it from premature drying, and keep it free of running water until final set. Do not work below 5C falling. For maximum durability, overcoat the cured repair with a Fosroc Dekguard anti-carbonation or protective coating system to extend service life.
Specifications
| Product type | Shrinkage-controlled, polymer-modified cementitious repair mortar (spray and hand grade) |
| Compressive strength (hand application, 28 days, BS 1881 Pt.116) | >50 N/mm2 |
| Compressive strength (spray application, 28 days, iterative) | >60 N/mm2 |
| Flexural strength (28 days, BS 6319 Pt.3) | >10 N/mm2 |
| Tensile strength (28 days, BS 6319 Pt.7) | >5 N/mm2 |
| Drying shrinkage (ASTM C 157-93) | <300 microstrain at 7 days; <500 microstrain at 28 days |
| Permeability (DIN 1048 Part 5) | <8 mm |
| Initial Surface Absorption (BS 1881 Pt.208) | 0.04% |
| Electrical resistivity (CP overlay use) | <20,000 Ohm-cm |
| Water addition | 4.25 to 4.5 litres per 25 kg bag (water:powder ratio ~0.18) |
| Minimum applied thickness | 10 mm |
| Maximum build, single spray application | Up to 150 mm overhead; up to 200 mm vertical |
| Yield | Approx 13.5 litres per 25 kg bag (at 4.25 L/bag) |
| Packaging | 25 kg bags |
| Minimum application temperature | Not below 5C and falling |
| Fire behaviour | Non-flammable, no fire hazard |
| Shelf life | 12 months in dry conditions (as low as 4 months in high heat/humidity) |
Industry use cases
Bridges and highway infrastructure
Spray reinstatement of spalled and section-loss concrete on bridge soffits, piers and crash-barrier zones, where high build and low rebound let crews repair large overhead areas quickly with minimal lane closure on national highways and urban flyovers.
Marine and ports
Repair of chloride-attacked seawalls, jetties, quays and breakwaters, using a Nitobond EP bond coat on damp substrates and the mortar’s low permeability to resist further saltwater and chloride ingress along India’s coastline.
Water-retaining and treatment structures
Large-area reinstatement inside reservoirs, water tanks and sewage/effluent structures where a durable, low-permeability spray-applied mortar is needed over extensive surfaces.
Industrial and power plants
Restoration of fire-damaged and chemically degraded concrete in plant structures, cooling towers and process buildings, including fast-track turnaround windows where speed of placement is critical.
Parking structures and commercial buildings
Overhead and vertical repair of carbonated, delaminated slabs, beams and columns in multi-storey car parks and ageing commercial concrete across Delhi NCR and metro cities, often paired with cathodic protection overlays.
Frequently asked questions
Can Renderoc SPXtra be hand-applied, or is it spray-only?
How much water do I add, and can I use part bags?
What thickness can I build in a single application?
How does it prevent the cracking that affects ordinary repair mortars?
Is it suitable for marine or constantly damp structures?
Can it be used with a cathodic protection system?
How we position Fosroc Renderoc SPXtra
Within the Fosroc Renderoc family, SPXtra is the spray-and-hand, high-build option for large-volume vertical and overhead repairs; it complements Renderoc HSXtra (hand-applied, high-strength structural repair), Renderoc S (standard hand-applied), and Renderoc GP (general purpose), and is typically used with Nitobond EP (bond coat), Nitozinc/Nitoprime (reinforcement primers), Concure (curing) and Dekguard (anti-carbonation protective coating) to form a complete EN 1504 repair-and-protect system. Compared with competitor spray and patch repair mortars such as Sika MonoTop and SikaRep, MBS (MYK Schomburg) Renostruct repair mortars, Dr. Fixit Krack-X/repair mortar range, and STP (Sika-owned) repair systems, Renderoc SPXtra’s clearest differentiator is its shrinkage-controlled formulation and very high single-pass build capacity, making it strong where fast, high-volume overhead spray repair with minimal cracking is the priority. For thin patch repairs, fairing coats or budget-led small-scale work, a hand-applied product such as Renderoc S or a competitor patch mortar may be more economical. Space Arc Engineering, as an authorised Fosroc distributor in Delhi NCR and Pan-India, can specify the correct Renderoc grade and ancillary system for each application and advise honestly where a simpler or alternative product is the better commercial fit.
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