Gunning castable, also called gunite, guniting material, or gunning mix, is a monolithic refractory applied pneumatically through a hose and nozzle, without formwork, making it the preferred method for hot repairs and difficult-access applications. Dense gunning mixes contain 40 to 70% Al2O3 and achieve service temperatures up to 1700°C; they are specified for hot repair of BOF vessels, EAF patches, blast furnace taphole areas, rotary kiln shell repairs, and steel ladle sidewall rebuilds. Insulating gunning mixes use lightweight aggregates such as perlite or vermiculite and achieve bulk densities of 0.8 to 1.4 g/cm3; they are used for boiler insulation linings and heat-conservation layers. Key selection parameters are operating temperature, chemical attack type (acid slag, basic slag, or cement clinker alkali), lining thickness, and whether the repair is hot-face or cold-face. Rebound loss in dry-process gunning is 15 to 25%; wet-process reduces this to 5 to 10% and improves bond strength. Shanker Agencies supplies Calderys and Mahakoshal gunning grades from Delhi NCR with same-week dispatch and CIF export to GCC and ASEAN.
What Is Gunning Castable? All Synonyms Explained
Gunning, gunite, and guniting all refer to the same pneumatic refractory application process. The mix is fed dry into a gunning machine, conveyed through a hose by compressed air, and water is added at the nozzle just before the material strikes the substrate. The impact velocity compacts the mix against the surface without any formwork required. This is called the dry process.
In the wet process (sometimes called shotcreting), the mix is pre-blended with water and pumped as a slurry; air velocity at the nozzle provides the final compaction force. The wet process produces less rebound and a more consistent water-to-cement ratio, but requires more specialised equipment and is less common in refractory hot-repair applications.
Equipment needed for dry-process gunning: a gunning machine (rotary-drum or pressure-vessel type), an air compressor providing 5 to 10 bar at 10 to 15 m3/min, a water ring at the nozzle with a flow meter, and a rubber hose typically 38 to 50mm bore.
Gunning is chosen over casting when hot repairs are needed during or between campaigns, when the geometry is too tight or angled to place formwork, when speed is critical, or when only a localised zone has eroded and shutting down adjacent equipment would be impractical. See also: when to choose gunning over casting for a full decision framework.
Dense vs Insulating Gunning Castable: Grade Comparison
The two main families are dense gunning castables (for hot-face structural repairs) and insulating gunning castables (for backup layers and heat conservation). Dense grades contain 40 to 70% Al2O3 and bond ceramically at high temperatures. Insulating grades use perlite or vermiculite aggregates for low bulk density and low thermal conductivity.
Dense 40% Al2O3 grades are used for general repair work up to 1450°C, with bulk density 2.0 to 2.2 g/cm3 and rebound loss 20 to 25%. Dense 50% grades handle up to 1550°C for boilers and preheaters (rebound 18 to 22%). Dense 60% grades are specified for ladle and kiln repairs up to 1650°C (rebound 15 to 20%). Dense 70% grades serve BOF, EAF, and blast furnace taphole applications up to 1700°C (rebound 15 to 18%). Insulating perlite-based grades operate to 900°C at 0.8 to 1.0 g/cm3. Vermiculite-based insulating grades reach 1100°C at 1.0 to 1.4 g/cm3.
Application Matrix: Which Grade for Which Equipment
Steel ladle sidewall hot repair uses dense 60 to 70% Al2O3 at 1600°C against basic slag, applied between campaigns. BOF vessel repair requires dense 70% at 1700°C against basic slag plus iron oxide during campaign downtime. Blast furnace taphole is repaired daily with dense 70% against iron and slag at 1650°C. EAF roof and sidewall patching uses 60 to 70% grade at 1650°C for rapid turnaround. Cement kiln preheater repair requires alkali-resistant 50 to 60% grade with SiC addition at 1100°C. Cement kiln burning zone shell repairs use 60 to 70% as a temporary fix before full relining. Power plant boiler combustion chambers use 60% Al2O3 plus SiC at 1100°C for flyash erosion resistance. FBC cyclones require 60 to 70% plus SiC at 950°C because of high-velocity flyash particle erosion. Foundry cupola tuyere and shaft repair uses dense 50 to 60% at 1400°C. Induction furnace collar and pouring spout repair uses dense 60% at 1550°C against steel and flux.
Cement Kiln Gunning: Alkali Attack and How to Prevent It
Standard gunning mixes fail rapidly in cement kilns because alkali compounds in cement clinker chemistry, primarily potassium sulphate (K2SO4) and sodium sulphate (Na2SO4), attack and destroy calcium aluminate bonds within weeks. Alkali-resistant gunning grades address this through silicon carbide addition of 3 to 8% or zircon addition of 5 to 10%, which resists the sulphate-alkali reaction. The applicable Indian Standard for cement kiln gunning materials is IS 8. Water addition at the nozzle should be 7 to 10% by weight. Application must be done with the kiln rotating slowly to prevent the applied mix from sagging on the hot surface. Do not gun onto surfaces above 700°C; allow cooling to 400 to 500°C for best adhesion and minimum rebound.
Alkali attack is most severe in preheater cyclone cones and riser ducts where alkali vapour concentration is highest. In these zones, plan for repair intervals of every 2 to 3 months using alkali-resistant grades. Waiting for visible failure before scheduling repair consistently results in larger affected areas and higher material quantities per intervention.
Power Plant and FBC Boiler Gunning
Fluidised bed combustion (FBC) boilers present the most aggressive refractory wear environment in the power sector. Flyash particles travel at 20 to 40 m/s and cause severe abrasive erosion on all hot-face surfaces. Standard high-alumina gunning grades wear rapidly in FBC service. The correct specification for FBC combustion chambers and cyclones is 60 to 70% Al2O3 with 10 to 15% SiC addition; the SiC provides the hardness needed to resist high-velocity particle erosion. Gunning is not recommended for FBC grate zones; use vibro-castable instead. For conventional pulverised coal boilers, the furnace chamber and burner zones use dense 50% Al2O3 gunning. The economiser and air preheater benefit from insulating gunning at 0.8 to 1.0 g/cm3 bulk density to reduce external heat losses.
Rebound Loss: What Causes It and How to Minimise It
Rebound loss is the percentage of material that bounces off the substrate during gunning and falls to the floor. In dry-process gunning, rebound is 15 to 25% for dense high-alumina mixes. Wet-process (shotcrete) gunning reduces rebound to 5 to 10% and improves bond strength through more consistent water distribution.
To minimise rebound: maintain nozzle distance of 0.5 to 1.0 m from the surface and hold the nozzle perpendicular to the substrate. Keep water addition at 7 to 12% by weight at the nozzle. Use a properly calibrated water ring with a flow meter; inconsistent water delivery is the primary cause of high rebound. Add microsilica to the mix where permitted (3 to 5% addition reduces rebound by 3 to 5%). Apply in layers of 20 to 30mm allowing initial set before the next layer. For material quantity calculation: volume needed multiplied by bulk density multiplied by 1.25 accounts for 20 to 25% rebound loss.
SAPL Gunning Castable Supply
Shanker Agencies maintains stock of Calderys India and Mahakoshal Refractories gunning grades at our Delhi NCR warehouse. Available grades include dense 50%, 60%, and 70% Al2O3 variants, alkali-resistant cement kiln grades with SiC addition, and insulating grades for boiler and heat conservation applications. Standard grades dispatch within the same week. CIF export to GCC destinations has a 7 to 14 day transit time; ASEAN destinations 10 to 21 days. Full material test certificates and certificates of origin are provided with every export shipment. Contact info@shankeragencies.com with your application details for a grade recommendation. View our full gunning castable range.
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Frequently Asked Questions
What is the difference between gunning castable and casting refractory?
Gunning castable is applied pneumatically through a hose and nozzle without formwork, relying on the impact velocity of the material to compact it against the substrate. Casting refractory is mixed with water to a pourable consistency and cast into formwork, then vibrated to remove air. Gunning is used for hot repairs during campaigns, difficult-access areas, and localised erosion zones where setting up formwork is impractical. Castable is used for new construction or full relining of standard geometries where high density and low porosity are critical. Gunning allows faster repairs with less downtime; casting typically achieves higher density and lower porosity in the finished lining.
What does gunite mean in refractory? Is it the same as gunning?
Yes, gunite and gunning are the same process in the refractory context. The term gunite originates from the construction industry where shotcrete was called gunite. In refractory applications, gunning, gunite, and guniting all refer to the pneumatic application of dry refractory mix through a hose and nozzle with water added at the point of application. The terms are used interchangeably across Indian and international refractory specifications. Some specifications refer to the material as gunning mix, gunning castable, or guniting material; all describe the same product category.
Which gunning castable grade is best for cement kiln repair?
For cement kiln preheater and calciner repairs, use an alkali-resistant gunning grade containing silicon carbide (3 to 8%) or zircon addition to resist K2SO4 and Na2SO4 attack. The alumina content should be 50 to 60% for preheater zones. For burning zone shell repairs, a 60 to 70% Al2O3 dense grade with alkali resistance is recommended. Standard high-alumina gunning mixes without alkali resistance fail rapidly in cement kiln service because calcium aluminate bonds are destroyed by sulphate-alkali reactions within weeks. Always specify alkali-resistant grades for cement kiln applications and allow the kiln to cool to below 700 degrees before gunning for best adhesion.
What is rebound loss in gunning and how can it be reduced?
Rebound loss is the percentage of gunning mix that bounces off the substrate instead of adhering. In dry-process gunning, rebound is typically 15 to 25% for dense high-alumina mixes, meaning you must order 20 to 25% more material than the net volume requires. To reduce rebound: maintain nozzle distance at 0.5 to 1.0 m from the surface; keep water addition at 7 to 12% by weight at the nozzle; use a properly calibrated water ring with a flow meter; add microsilica (3 to 5%) to the mix where the specification allows; apply in 20 to 30mm layers allowing initial set before the next layer. Wet-process gunning reduces rebound to 5 to 10% but requires different equipment.
What gunning material is used for power plant FBC boilers?
For fluidised bed combustion (FBC) boiler combustion chambers and cyclones, specify dense gunning castable with 60 to 70% Al2O3 and 10 to 15% silicon carbide addition. The SiC content is essential because FBC service involves flyash particles at 20 to 40 m/s velocity causing severe abrasive erosion; standard alumina grades without SiC wear rapidly. For FBC grate areas, gunning is not recommended; use vibro-castable instead. For conventional pulverised coal boilers, 50% Al2O3 dense gunning is standard for furnace chamber and burner zones. Insulating gunning at 0.8 to 1.0 g/cm3 is used for economiser and air preheater sections to reduce external heat loss.
Where can I buy gunning castable in India with export capability?
Shanker Agencies Pvt. Ltd. supplies Calderys and Mahakoshal gunning castable grades from our Delhi NCR warehouse with same-week dispatch for standard grades. We export CIF to GCC destinations (UAE, Saudi Arabia, Qatar, Oman, Kuwait, Bahrain) with 7 to 14 days transit, and to ASEAN destinations (Singapore, Malaysia, Indonesia, Vietnam, Thailand) with 10 to 21 days transit. All export shipments include material test certificates and certificates of origin. Contact info@shankeragencies.com or call +91-9899957888 with your application details and required grade for a quotation.