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1. Fire Door Construction and Core Materials

Steel fire doors are required by building codes to maintain structural integrity and thermal insulation for a specified duration when exposed to fire — typically 30, 60, 90, or 120 minutes. The door achieves this performance through a non-combustible core material enclosed within steel face sheets. The core is the functional element: it blocks heat transfer from the fire side to the non-fire side, prevents flame penetration, and provides a solid substrate for hinge, lock, and closer attachment.

Four core materials dominate the fire door manufacturing industry today:

• Calcium silicate board. The subject of this page. Xonotlite-based, autoclave-cured, inorganic. Offers the highest strength-to-weight ratio among non-combustible core materials, consistent thickness across the entire board, and the best screw retention performance.
• Vermiculite board. Exfoliated vermiculite bonded with inorganic binder. Fire resistance is good but mechanical properties are lower than calcium silicate. Screw pull-out strength is approximately 40-60% that of calcium silicate at equivalent density. Thickness consistency varies between manufacturers.
• Gypsum board. Calcium sulfate dihydrate (CaSO₄·2H₂O). Effective fire barrier due to endothermic dehydration releasing water vapor. However, gypsum loses mechanical strength after dehydration and the board becomes friable. Screw retention after fire exposure is poor. Also susceptible to moisture damage during storage and transport.
• Perlite board. Expanded perlite with inorganic binder. Lowest cost but also lowest strength. Screw retention insufficient for heavy commercial door hardware without reinforcement plates. Higher thickness required for equivalent fire rating.

The fireproof door core material selection determines the door's fire rating, weight, hardware durability, manufacturing process, and delivered cost. Calcium silicate has become the dominant core material for premium and code-critical fire doors because it simultaneously satisfies fire performance, mechanical requirements, and manufacturing efficiency.

2. GF-1100 Fireproof Core Board Specifications

The GF-1100 series is a calcium silicate board specifically formulated for fire rated door core board applications. The formulation balances density, mechanical strength, and thermal performance for fire door manufacturing.

Board dimensions are selected to match standard door leaf sizes with minimal cutting waste. The 2100×950mm and 2150×950mm panels are designed for single-leaf door production. The 2440×1220mm panel accommodates larger door leaves and double-leaf assemblies. Custom thicknesses outside the standard range can be produced for specific fire rating requirements or door designs.

The board surface is sanded to a smooth, consistent finish. No additional surface preparation is required before adhesive application and steel sheet facing. The board edges are square-cut and clean; edge profiling (rebates, chamfers) can be machined on request.

3. Fire Resistance Performance

The fire resistance of a calcium silicate core door derives from two mechanisms: (1) the inherently low thermal conductivity of the xonotlite crystal structure, which resists heat transfer from the fire side to the non-fire side, and (2) the endothermic dehydration of chemically bound water within the xonotlite crystal.

The dehydration reaction, which occurs at approximately 400-450°C, absorbs approximately 550 kJ per kilogram of chemically bound water released. A 40mm thick GF-1100 core of density 400 kg/m³ in a standard door leaf (approximately 2.0 m²) contains approximately 32 kg of calcium silicate. With bound water content of approximately 12% by weight, the dehydration absorbs roughly 2,100 kJ of heat energy from the fire — energy that would otherwise heat the non-fire side of the door. This endothermic plateau delays the temperature rise on the non-fire side, contributing directly to the door's fire resistance duration.

Fire rating by core thickness:

*180-minute rating with 50mm core is achievable but depends on door frame design, intumescent seal specification, glazing (if any), and the specific testing configuration. Each door design must be individually fire-tested to the target standard by an accredited laboratory.

The GF-1100 core contributes no fuel to a fire, produces no visible smoke (smoke developed index 0 per ASTM E84), and generates no flaming droplets. After fire exposure, the core retains its structural form, though mechanical properties are reduced by the dehydration. The residual structure continues to provide thermal insulation, which is important for maintaining the door's integrity through the full fire resistance duration.

4. Comparison with Alternative Core Materials

Calcium silicate delivers the best combination of fire performance, mechanical properties, manufacturing consistency, and handling characteristics. The material cost is higher than perlite or gypsum, but total door manufacturing cost — including rejection rate, hardware reinforcement requirements, and field warranty claims — is typically lower. Door manufacturers report that switching from perlite to calcium silicate core reduces factory rejection rates by 50-70% due to the board's consistent thickness and better screw retention eliminating stripped threads and loose hardware.

5. Door Manufacturing and Fabrication

The GF-1100 core board integrates into standard fire door production lines with minimal process changes:

Cutting to size. Boards are cut to the required door leaf dimensions using standard woodworking panel saws with carbide-tipped blades. A 40-tooth alternate top bevel (ATB) blade produces clean edges with no chipping. Dust extraction is recommended — the dust is inert and non-toxic (calcium silicate plus reinforcing fibers) but, like any fine dust, should not be inhaled. Standard workshop dust masks and ventilation are adequate.

Edge profiling. For door designs requiring rebated edges (for intumescent strip installation or door frame sealing), the core board edge can be profiled using a router or spindle moulder with carbide tooling. The board machines cleanly and holds a sharp edge profile.

Steel sheet adhesion. The core board is supplied sanded and ready for facing. Steel door skins (typically 0.8-1.2mm galvanized steel) are bonded to the core using a two-component polyurethane or epoxy structural adhesive applied by roller or curtain coater. Open time of 10-20 minutes provides adequate working time for assembly. The assembled door leaf is cold-pressed or vacuum-pressed for adhesive curing. For manufacturers using a hot press (60-80°C), the calcium silicate core is dimensionally stable and does not outgas during the press cycle.

Hardware installation. Hinges, locks, closers, panic bars, and door handles are fixed through the steel skin into the calcium silicate core with self-tapping screws. For heavy commercial hardware (door closers, panic exit devices), reinforcement plates are recommended. These can be steel backplates installed between the core and the steel skin, or through-bolts with nuts on the interior face. The core board provides reliable screw retention without the need for plastic wall plugs or chemical anchors — the screw thread cuts directly into the calcium silicate matrix.

No special personal protective equipment beyond standard workshop PPE is required when working with GF-1100 boards. The material contains no respirable crystalline silica hazard at the levels relevant to door manufacturing operations.

6. Quality Assurance and Fire Testing

Every production batch of GF-1100 core board is tested for density, moisture content, and compressive strength before dispatch. Samples are retained from each batch for a minimum of five years to support regulatory traceability.

Batch testing protocol: From each production run, a minimum of three boards are selected for testing. Density is determined on full-size boards by weight and dimensional measurement. Moisture content is measured by oven-drying a 100×100mm sample at 105°C to constant weight. Compressive strength is tested on 50×50mm specimens cut from the sample boards, tested at 10% strain per ASTM C165. Test results must meet the specification in Section 2 above before the batch is cleared for packing and shipment.

Fire resistance certification. The GF-1100 core board has been fire-tested in complete door assemblies to GB 12955 (Fire Resistant Doorsets) and EN 1634-1 (Fire Resistance and Smoke Control Tests for Door and Shutter Assemblies) at CNAS-accredited fire testing laboratories. Test reports document the door construction details, core thickness, and achieved fire resistance duration. These reports are available to door manufacturers for inclusion in their own certification submissions to building control authorities.

Ongoing compliance. Mingfa maintains a type-testing program with annual re-testing of representative door constructions to verify continued performance consistency. Any formulation or process change that could affect fire performance triggers a re-test before implementation. This program supports door manufacturers' obligations under construction products regulations requiring evidence of ongoing conformity of production.

7. Ordering for Door Manufacturers

GF-1100 core board is supplied in the following standard formats:

Custom cutting service. Mingfa offers a pre-cut service where boards are cut to exact door leaf dimensions before packing. This reduces handling, eliminates in-factory cutting waste, and simplifies material flow in the door manufacturing plant. Minimum order quantity applies for pre-cut sizes.

Container-optimized packaging. Boards are packed on ISPM 15 fumigated pallets with corner protection boards, wrapped in waterproof polyethylene film, and strapped with steel or PET banding. Pallet dimensions and loading patterns are optimized for maximum container utilization — typically 22-24 pallets per 40-foot high-cube container, depending on board thickness and panel size.

Sample boards. 300×300mm sample boards at standard thicknesses are available for initial evaluation and testing. Contact us through the inquiry form specifying the thickness(es) you need. Samples are provided at no charge; customer arranges or covers freight.

MOQ and lead time. Minimum order quantity is one pallet per thickness/size combination. Standard lead time is 15-25 working days. Rush orders for smaller quantities can be accommodated. Contact us with your annual door production volume and core specification for a long-term supply quotation.

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