Refractory Mortars & Binders

Air-setting mortars develop strength through hydraulic reaction at ambient temperature (12-24 hours setting time) and are ready for heating after 24-48 hours drying. They use calcium aluminate cement (CAC) as the primary binder and achieve 20-40 MPa cold crushing strength.

Heat-setting mortars develop strength primarily during the initial heat-up when ceramic bonding occurs at 800-1200°C, requiring controlled heating rates (25-50°C/hour up to 600°C). They use fine refractory aggregates with minimal binder content (2-5% CAC) and achieve 40-70 MPa hot modulus of rupture at service temperature.

Air-setting mortars are preferred for general bricklaying with long installation times, while heat-setting mortars are used for high-temperature zones where ceramic bonding provides superior refractoriness (up to 1800°C).

For standard 3mm joint thickness (optimal for most refractory bricks), typical mortar consumption is 35-45 kg per square meter of wall surface. Thinner joints (2mm) require 25-30 kg/m², while thicker joints (5mm) need 50-60 kg/m².

Factors affecting consumption include brick dimensions (smaller bricks create more joints), joint thickness consistency, wastage (typically 5-10%), and application method (troweling vs. extrusion).

For a 50m² furnace wall with 3mm joints using standard 230×114×65mm bricks, expect to use approximately 2,000-2,250 kg of mortar. Always order 10-15% extra to account for mixing losses, joint variations, and filling irregular surfaces.

High-alumina cement (HAC or CAC - Calcium Aluminate Cement) is a rapid-hardening hydraulic cement containing 40-80% Al₂O₃, significantly higher than Portland cement's 5% Al₂O₃. In refractory mortars, CAC provides excellent high-temperature performance with a melting point of 1400-1750°C depending on alumina content.

CAC mortars provide:

• Rapid strength development (70% of final strength in 24 hours)
• Excellent thermal shock resistance due to similar thermal expansion as refractory bricks (6-8 × 10⁻⁶/°C)
• Maintained strength at elevated temperatures up to 1000-1300°C
• Resistance to chemical attack from slags and process gases

Common grades include CAC-50 (50-55% Al₂O₃, up to 1450°C), CAC-70 (70-75% Al₂O₃, up to 1650°C), and CAC-80 (80% Al₂O₃, up to 1750°C). CAC is the most widely used binder for refractory mortars globally due to its unique combination of hydraulic setting, high refractoriness, and chemical stability.

Yes, specialized hot repair mortars (plastic refractories and hot patching compounds) can be applied to furnace surfaces at temperatures of 800-1400°C while the unit remains in operation.

These mortars:

• Contain heat-resistant binders (phosphate or colloidal silica)
• Feature fine refractory aggregates and chemical setting agents that activate at elevated temperatures
• Are applied by hand troweling or pneumatic gunning in 10-50mm thick layers
• Adhere to hot surfaces through rapid dehydration and sintering
• Develop working strength within 30-120 minutes
• Cure fully during continued operation

They are ideal for emergency repairs of spalling areas, crack sealing in hot zones, extending campaign life of damaged linings, and avoiding costly shutdowns. However, hot repairs are temporary solutions; permanent repairs require cold rebuilding during scheduled maintenance shutdowns.

Refractory mortars have a typical shelf life of 6-12 months from manufacturing date when stored properly in sealed, moisture-proof bags. High-alumina cement-based mortars are particularly sensitive to moisture absorption, which causes pre-hydration and loss of binding properties.

Proper storage requires:

• Keeping bags on pallets off direct ground contact
• Storing in dry, covered warehouses with <60% relative humidity
• Maintaining cool temperatures (15-25°C, avoiding >35°C)
• Keeping original sealed packaging intact until use
• Implementing first-in-first-out inventory rotation
• Avoiding freezing temperatures for phosphate-bonded mortars

Signs of degraded mortar include lumping or hardening in the bag, extended setting time (>36 hours), reduced strength after setting, and difficulty achieving proper consistency.

For long-term storage beyond 12 months, perform trial batches to verify setting time and strength before large-scale use.

Refractory mortars are tested and certified according to ASTM C860 (Standard Specification for Refractory Mortar) which covers classification, testing, and acceptance criteria.

Key testing standards:

• ASTM C860 - Mortar classification and properties
• ASTM C198 - Modulus of rupture by cold crushing
• ASTM C133 - Cold crushing strength of dried specimens
• ASTM C874 - Rotary mixer for mortar preparation
• ASTM C1672 - Bond strength of refractory mortar
• ISO 1927 - International standard for refractory mortars

Quality certifications:

• ISO 9001:2015 - Quality management for production
• ISO 14001:2015 - Environmental management
• CE marking - European conformity for export markets

Manufacturers should provide mill test certificates (MTC) with chemical analysis and physical properties, technical data sheets (TDS) with application guidelines, and material safety data sheets (MSDS) for safe handling. Third-party inspection available through SGS, Bureau Veritas, and Intertek for export shipments.