Preparation Methods Of 10 Types Of Common Refractory Mortars And Their Application Scenarios in Various Industries

Refractory mortar (also known as fire clay or refractory slurry) is a monolithic refractory material composed of refractory powder (aggregate), binder and admixtures. It is supplied in powder form. After mixing with water or special liquid, it becomes plastic. It is specially used for jointing refractory bricks, repairing furnace linings and surface coating. At high temperatures, it can sinter integrally with bricks, featuring sealing & refractory performance, thermal shock resistance and slag corrosion resistance.

Bricklaying & Bonding (Core Application)

Fill 2～5 mm gaps between refractory bricks, bonding individual bricks into an integrated furnace lining. It realizes sealing against leakage, load bearing and heat insulation, reducing heat loss by 15%～20% compared with conventional bricklaying.

Repairing & Pointing

After kiln operation, when brick joints crack, local spalling or holes occur, apply or spray repair-grade refractory mortar for rapid restoration of air tightness and strength, extending furnace lining service life by 1～3 years.

Protective Coating

Apply a thin coating (2～3 mm) on furnace lining surface to improve slag & flue gas corrosion resistance, lower surface heat dissipation and mitigate thermal shock damage.

Other Uses

Seam filling for thermal insulation pipelines, expansion joint filling, wrapping and sealing of anchors, etc.

① Fireclay mortar: 100% fireclay refractory mortar, add 400~600 L water per cubic meter of dry material.

② Fireclay-bauxite cement mortar: fine-grained fireclay refractory mortar 90%, bauxite cement 10% (volume ratio).

100% siliceous refractory mortar, add 400~600 L water per cubic meter of dry material.

100% high-alumina refractory mortar, add 400~600 L water per cubic meter of dry material.

① Fireclay mortar: 100% fireclay refractory mortar, add 400~600 L water per cubic meter of dry material.

② Diatomite powder-bonding clay mortar: diatomite powder 60%~70%, bonding clay 40%~30% (volume ratio), add 400~600 L water per cubic meter of dry material.

③ Cement-diatomite mortar: cement : diatomite powder = 1:5 (mass ratio), add 400~600 L water per cubic meter of dry material.

④ Diatomite-fireclay refractory mortar: calcined diatomite powder 65%, medium-grained fireclay refractory mortar 25%, portland cement 10% (mass ratio).

① Vermiculite powder mortar: portland cement 30%, fireclay refractory mortar 30%, expanded vermiculite powder (particle size <3 mm) 40% (mass ratio).

② Diatomite-fireclay refractory mortar: calcined diatomite powder 65%, medium-grained fireclay refractory mortar 25%, portland cement 10% (mass ratio).

③ Fireclay mortar: 100% fireclay refractory mortar, add 400~600 L water per cubic meter of dry material.

① The adopted bauxite clinker shall be Grade I high-alumina bauxite, calcined at 1600℃ in rotary kiln and processed. Its micro powder is ground by ball mill with specific surface area of 4000~4500 cm²/g.

② Preparation steps of aluminum phosphate solution: a. Weigh phosphoric acid, aluminum hydroxide and water proportionally; pour water into aluminum hydroxide and keep stirring continuously. b. Heat phosphoric acid to around 70℃. c. Add the aluminum hydroxide-water slurry into phosphoric acid in batches with continuous stirring until the solution turns clear. d. After cooling, filter the solution with gauze and store in containers for later use.

Tools and containers (stirring rods, trowels, mortar buckets, etc.) for phosphoric acid, solution and mortar shall be made of ceramic, enamel, wood or stainless steel. Iron or aluminum containers/tools which react easily with acid are prohibited. The relative density of aluminum phosphate solution shall be controlled at 1.56~1.59 (20℃).

For large-batch solution preparation, cold mixing method is available: place phosphoric acid in large ceramic vat in advance; mix aluminum hydroxide with boiling water to form slurry, add into phosphoric acid in batches while stirring. Do not add the next batch until the reaction between the previous aluminum hydroxide slurry and phosphoric acid is nearly complete. The final solution shall be clear, then test and adjust its relative density.

③ For mortar preparation: mix dry materials uniformly first, then pour aluminum phosphate solution into dry mixture and stir thoroughly for application. If iron mill scale powder is used, aluminum hydroxide and refractory cement are not required in dry blend. However, the mixture shall be kept in air for 24 hours to release gas before use.

④ For repairing high-temperature industrial furnaces: treat the repair area until hard substrate is exposed. Dip a brush or other tools with a small amount of aluminum phosphate solution and coat the repair surface for wetting (avoid excessive coating), then carry out repair work. When used as bonding mortar, remove dust and oil from the surfaces of bonded parts; roughening the surface is recommended before bonding.

⑤ The heating rate during heat treatment shall not exceed 10~20℃/h.

⑥ This material gains strength slowly at ambient temperature and is prone to deliquescence under humid conditions. Avoid collision and keep surrounding environment dry before heat treatment.

① Formula 1: slag portland cement 50%, calcined clay powder (<3 mm) 50% (mass ratio).

② Formula 2: portland cement 20%, calcined clay powder 50%, fireclay refractory mortar 30% (mass ratio).

① Formula 1: low-calcium aluminate cement 50%, bauxite clinker powder (<3 mm) 50% (mass ratio).

② Formula 2: low-calcium aluminate cement 1 part, bauxite clinker powder 3~5 parts (mass ratio).

③ Formula 3: 100% bauxite clinker powder, add water glass (relative density 1.32~1.4) 20%~30% (mass ratio).

100% calcined clay powder, add industrial phosphoric acid (relative density 1.32~1.4) 25% (mass ratio).

Magnesia refractory mortar is used for laying magnesia bricks or magnesia-chrome bricks. Normally magnesia refractory mortar is pre-mixed by suppliers. Users only need to mix it with water glass diluted to relative density of 1.41~1.44 (diluted by 40%~50% water) to form paste for construction.

If self-prepared from raw materials: fine magnesia sand, magnesia fine powder (φ<1 mm, specific surface area 2000~2500 cm²/g), fine iron ore powder (φ<1 mm) and water glass (diluted with water at volume ratio 1:5). In hot southern regions, dilute water glass and water at volume ratio 1:1. The mass ratio of the three raw materials is 1:1:1. Mix well to obtain dry powder. Add diluted water glass accounting for about 30% of dry powder mass into dry powder and stir to get proper paste.

If wider mortar joints are required, properly increase magnesia grain size. If mortar sets slowly, uniformly blend about 0.5% portland cement into dry powder as setting accelerator. Do not prepare excessive mortar at one time to avoid premature setting during construction. If setting occurs, add appropriate water glass and stir evenly for reuse. Prepare magnesia refractory mortar at 8%~10% of brick volume.

Blast Furnace / Hot Blast Stove: Fireclay refractory mortar (≤1350℃) matched with fireclay bricks; high-alumina refractory mortar (Al₂O₃ ≥60%, 1200～1500℃) matched with high-alumina bricks, applied to furnace shaft and hot blast stove crown.

Steelmaking Converter / Ladle / Tundish: Magnesia refractory mortar (MgO ≥70%, ≥1600℃) matched with magnesia bricks / magnesia-chrome bricks, resistant to alkaline slag corrosion; high-alumina / corundum type used below the slag line of ladles.

Reheating Furnace / Heat Treatment Furnace: High-alumina type (1200～1400℃) for furnace walls and crowns; fireclay type for low-temperature zones (≤1200℃) such as flues and furnace doors.

Cement Rotary Kiln: Magnesia / magnesia-spinel refractory mortar (≥1600℃, alkali salt corrosion resistant) for burning zone; high-alumina / neutral refractory mortar for transition zone; fireclay / high-alumina type for preheating zone and cooling zone.

Glass Melting Furnace: Siliceous refractory mortar (SiO₂ ≥90%, 1400～1500℃) matched with silica bricks, used for furnace crown, regenerator and flue; high-alumina type for charging port and throat; zirconia-corundum type for heavily eroded areas.

Ceramic / Brick & Tile Tunnel Kiln: Fireclay mortar for preheating zone (800～1100℃); high-alumina mortar for burning zone (1200～1400℃); high-alumina / cordierite mortar for roller kilns, featuring thermal shock resistance and wear resistance.

Coke Oven: Siliceous refractory mortar (1300～1450℃) matched with silica bricks, used for combustion chamber, regenerator, furnace crown and flue, resisting corrosion from high-temperature coal gas and ash residues.

Boiler / Cracking Furnace: Fireclay type (≤1200℃) for furnace chamber, flue and chimney; high-alumina type for superheater and radiation chamber; lightweight refractory mortar for joints of thermal insulation layers.

Vertical Lime Kiln / Active Lime Kiln: High-alumina type (1200～1400℃) matched with high-alumina bricks; magnesia type for burning zone (≥1500℃), resistant to lime melt corrosion.

Aluminum Reduction Cell: Carbon / magnesia refractory mortar, resistant to cryolite corrosion and reducing atmosphere.

Household / Commercial Stoves: Ordinary refractory mortar (≤1200℃) for masonry and repair of firewood stoves, ground pots and fireplace hearths.