What Is Calcium Silicate Insulation? A Technical Guide for Industrial Engineers

Published: 2026-07-07 | By Mingfa Technical Team

Industrial engineers specifying thermal insulation for high-temperature equipment face a crowded field of materials, from ceramic fiber blankets to mineral wool boards. Among these options, calcium silicate insulation occupies a specific niche: it is the rigid, load-bearing solution for continuous operating temperatures from ambient through 1100 degrees Celsius. This guide covers what calcium silicate is, how it is manufactured, how it performs under thermal and mechanical load, and where it is deployed in industrial plants worldwide.

At Laizhou Mingfa Insulation Materials Co., Ltd., founded in 1991 in Shandong Province, China, calcium silicate has been the sole product focus for over three decades. The company operates a 108,000-square-meter factory with fixed assets of 46.24 million yuan and holds approximately 20 national patents. Products are exported to cement, steel, aluminum, glass, and petrochemical clients across more than 40 countries.

1. What Is Calcium Silicate Insulation?

Calcium silicate insulation is a rigid, inorganic thermal insulation material produced by reacting lime (CaO) with silica (SiO₂) in water under high-pressure saturated steam. The primary reaction product is xonotlite, a crystalline calcium silicate hydrate phase with the chemical formula 6CaO·6SiO₂·H₂O. This crystalline structure is what gives the material its combination of thermal stability, mechanical strength, and dimensional integrity at elevated temperatures. Unlike fibrous insulation products that rely on trapped air within a random fiber matrix, calcium silicate derives its insulating properties from the microscopic pore structure built into the crystalline lattice during synthesis.

The transformation from raw materials to finished industrial board takes place inside large cylindrical autoclaves operating at temperatures of 190 degrees Celsius to 220 degrees Celsius under saturated steam pressure. Under these hydrothermal conditions, the CaO-SiO₂-H₂O system preferentially forms needle-like xonotlite crystals that interlock to produce a rigid, porous solid. The autoclave curing step typically runs for 8 to 16 hours depending on the density grade and formulation. Following curing, the boards are dried to remove free water, then precision-sanded to achieve the specified thickness tolerance, usually plus or minus 1.0 millimeter for standard grades. All Mingfa products are 100 percent asbestos-free. The raw material formulation uses only silica flour, quicklime, cellulose fiber reinforcement, and processing aids. No asbestos or substitute mineral fibers are added at any stage.

The resulting board is white to off-white in color, with a smooth, sanded surface on both faces. It can be cut with carbide-tipped woodworking tools, drilled, and machined to complex shapes without crumbling, a property that sets it apart from most other rigid high-temperature insulation materials. This machinability, combined with load-bearing strength, makes it practical for direct contact with refractory linings in kilns, furnaces, and process vessels.

2. The Manufacturing Process: From Raw Materials to Finished Board

Production of consistent calcium silicate insulation requires precise control over raw material ratios, slurry preparation, and autoclave cycle parameters. The process begins with dry blending of finely ground silica powder and calcium oxide in stoichiometric proportions targeting the xonotlite phase. Water is added to form a pumpable slurry, typically at a water-to-solids ratio that yields the target final density. Cellulose fibers are incorporated at 3 to 8 percent by weight to provide green strength for handling the uncured boards. The slurry is poured into molds sized for the finished board dimensions plus a shrinkage allowance, since the boards contract slightly during drying.

After molding, the filled molds are loaded into horizontal autoclaves capable of maintaining saturated steam at 1.2 to 2.3 MPa. The autoclave cycle profile is specific to each product grade. Lower-density boards in the 200 to 300 kilograms per cubic meter range require lower slurry solids content and longer curing times to develop adequate crystal interconnectivity. Higher-density grades at 600 to 900 kilograms per cubic meter use higher solids content and may require multiple filling and pressing stages before autoclaving. Following autoclave curing, the boards are removed from molds and dried in multi-zone tunnel dryers where temperature ramps from 80 degrees Celsius to 180 degrees Celsius over 24 to 48 hours. The dried boards are then cut to final dimensions and surface-sanded to thickness specification. Every production batch undergoes quality control testing per ASTM C533 and internal standards. Tests include bulk density (ASTM C303), compressive strength (ASTM C165), flexural strength (ASTM C203), linear shrinkage after reheating (ASTM C356), and thermal conductivity by guarded hot plate (ASTM C177 or C518). Test certificates ship with each export order.

Density is the primary variable that engineers use to select the right product grade. Standard insulation grades run from 200 to 300 kilograms per cubic meter. High-strength grades for load-bearing applications range from 400 to 900 kilograms per cubic meter. Mingfa produces the full density spectrum: LG-Standard (nominal 230 kilograms per cubic meter, rated 1000 degrees Celsius), LG-High Temperature (nominal 270 kilograms per cubic meter, rated 1100 degrees Celsius), and MF-HD high-density (800 to 850 kilograms per cubic meter for steel ladle backup lining).

3. Temperature Grades and ASTM C533 Classification

ASTM C533, the standard specification for calcium silicate block and pipe thermal insulation, defines two temperature classifications. Type I is rated for continuous use at hot-face temperatures up to 649 degrees Celsius (1200 degrees Fahrenheit). Type II is rated up to 927 degrees Celsius (1700 degrees Fahrenheit). These ratings reflect the temperature at which the material will exhibit linear shrinkage not exceeding 2.0 percent and maintain at least 90 percent of its original compressive strength after a 24-hour exposure. In practice, this means the board does not undergo significant phase transformation or microstructural degradation below its rated temperature. The margin between Type I and Type II is substantial: a Type I board placed in a 927-degree-Celsius service environment would shrink beyond 2 percent, lose mechanical integrity, and likely crack or spall.

Products produced by Laizhou Mingfa can exceed the Type II rating. The LG-Standard series is specified for continuous service at 1000 degrees Celsius. The LG-High Temperature series is rated to 1100 degrees Celsius. These elevated ratings arise from formulation adjustments made during years of production experience: finer silica particle size distribution, optimized CaO-to-SiO₂ molar ratio, and the addition of proprietary mineral stabilizers that suppress undesirable phase transformations at temperatures above 900 degrees Celsius. Selecting the correct temperature grade requires using the continuous operating hot-face temperature, not the peak excursion temperature. If a cement kiln shell normally operates at 350 degrees Celsius but can briefly reach 450 degrees Celsius during a process upset, the 650-degree-Celsius Type I rating provides an adequate factor of safety. But a glass furnace crown backup insulation that runs continuously at 800 degrees Celsius should not use a grade rated below 1000 degrees Celsius.

The practical consequence of exceeding a board’s rated temperature is progressive degradation: xonotlite gradually converts to wollastonite (CaSiO₃) at temperatures above 800 degrees Celsius in the absence of stabilizers, and wollastonite formation is accompanied by a volume change that causes micro-cracking and loss of strength. Mingfa’s stabilizer technology slows this conversion, allowing the LG-High Temperature grade to maintain xonotlite-phase dominance up to 1100 degrees Celsius.

4. Thermal and Mechanical Properties

Thermal conductivity of calcium silicate insulation follows a linear relationship with mean temperature. At a mean temperature of 100 degrees Celsius, conductivity is approximately 0.056 watts per meter-Kelvin. The accepted linear regression for standard grades is the general formula lambda equals 0.056 plus 0.00011 times the mean temperature t in degrees Celsius, yielding approximately 0.078 watts per meter-Kelvin at 200 degrees Celsius mean and 0.100 watts per meter-Kelvin at 400 degrees Celsius mean. Higher-density grades have slightly higher conductivity because the reduced porosity means less insulating air space. For example, a board at 800 kilograms per cubic meter will conduct roughly 15 to 20 percent more heat than a 230-kilogram-per-cubic-meter board of the same thickness and temperature differential.

Mechanical strength varies directly with density. A standard 230-kilogram-per-cubic-meter board typically achieves compressive strength of 2.0 to 3.0 megapascals per ASTM C165, with flexural strength of 0.8 to 1.2 megapascals per ASTM C203. Stepping up to a high-density 800-kilogram-per-cubic-meter grade raises compressive strength to 10 to 15 megapascals and flexural strength to 4 to 6 megapascals. The strength is directionally dependent: values measured perpendicular to the board face (through-thickness compression) typically exceed in-plane compression by 10 to 20 percent. This directional behavior reflects the slight alignment of xonotlite crystals during molding. Linear shrinkage after 24-hour exposure at the rated temperature is controlled to under 2.0 percent across all grades. In practice, well-stabilized formulations typically exhibit shrinkage of 0.5 to 1.2 percent at their maximum rated temperature, well within the ASTM C533 limit. The practical implication for engineers is that a 50-millimeter-thick board will lose at most 0.6 millimeter of thickness at full rated temperature, maintaining adequate contact with the hot face and preventing thermal bypass gaps.

Density also affects handling characteristics. A 230-kilogram-per-cubic-meter board sized 600 by 300 by 50 millimeters weighs approximately 2.1 kilograms, manageable for single-person installation. An 800-kilogram-per-cubic-meter board of the same dimensions weighs roughly 7.2 kilograms, requiring two-person handling or mechanical assistance for large installations. The trade-off between insulation value, strength, and handling weight is a central consideration in product selection.

5. Where Calcium Silicate Insulation Is Used

Cement rotary kilns represent one of the largest application segments. The LG-Standard (1000-degree-Celsius) grade in 230-kilogram-per-cubic-meter density is installed as backup insulation between the steel kiln shell and the refractory brick working lining. Typical thickness is 25 to 40 millimeters. The insulation reduces shell temperature by 40 to 80 degrees Celsius, cutting radiant heat loss and protecting the steel from creep deformation. A 5000-tonne-per-day clinker line may consume 2000 to 5000 square meters of calcium silicate board per kiln section, depending on the kiln diameter and insulation specification.

In steelmaking, calcium silicate serves as permanent backup lining for ladles, tundishes, and electric arc furnace shells. The MF-HD high-density grade at 800 to 850 kilograms per cubic meter provides compressive strength exceeding 12 megapascals, sufficient to support the weight of a full refractory working lining plus the molten steel load without crushing. Thickness ranges from 20 to 50 millimeters. A 150-tonne steel ladle lined with 40 millimeters of MF-HD board behind 200 millimeters of magnesia-carbon brick operates with a shell temperature roughly 50 to 70 degrees Celsius cooler than an uninsulated equivalent.

Aluminum reduction cells (Hall-Heroult cells) use the MFDJ series composite brick, rated to 1000 degrees Celsius, for sidewall and cathode insulation. Density is specified at 400 to 600 kilograms per cubic meter to balance insulation value with the compressive load from the cathode assembly and the frozen cryolite ledge. Glass furnace crowns and sidewalls use MFBL series composite brick in densities from 300 to 850 kilograms per cubic meter, depending on whether the board serves as crown insulation (lower density) or sidewall backup (higher density, load-bearing). Petrochemical plants use calcium silicate pipe sections and boards for steam lines, reformer vessels, and reactor insulation where operating temperatures of 400 to 650 degrees Celsius are common. Fireproof door cores use the GF-1100 Super Calcium Silicate board at 350 to 450 kilograms per cubic meter, providing A1 non-combustible classification per EN 13501-1 and 120-minute fire resistance in certified door assemblies.

For asbestos replacement in legacy equipment, calcium silicate offers a direct substitute. Many industrial plants built before 1990 used asbestos-containing insulation boards that now require removal. Calcium silicate boards with the same thickness and density specifications can replace these materials with equivalent or better thermal performance and none of the health hazards.

6. Ordering Calcium Silicate Insulation: What to Specify

Placing an accurate purchase order for calcium silicate insulation requires specifying several parameters. Standard board dimensions range from 600 by 300 millimeters to 1200 by 600 millimeters, with special sizes available on request. Thickness is specified from 20 millimeters up to 120 millimeters in 10-millimeter increments, though any thickness within this range can be produced. The density grade determines both thermal and mechanical properties: specify the target density or product series name (for example, LG-Standard at 230 kilograms per cubic meter, or MF-HD at 800 to 850 kilograms per cubic meter). The temperature rating must be stated explicitly, especially when the order covers multiple grades for different service zones within the same project.

Quantity should be specified in square meters or in piece count with dimensions. Export orders from Mingfa typically ship from Qingdao port, approximately three hours by road from the Laizhou factory. Standard lead time is 15 to 30 days for container-load quantities, depending on the product mix and current production schedule. Custom dimensions, special density grades, and machined shapes add 5 to 10 days. Documentation provided with each shipment includes the commercial invoice, packing list, bill of lading, certificate of origin (Form E for ASEAN destinations, Form F for Chile, etc.), and the batch test certificate showing density, compressive strength, thermal conductivity, and linear shrinkage results per the relevant ASTM standards. For projects requiring third-party inspection, SGS or Bureau Veritas witness testing can be arranged at the factory laboratory with advance notice.

A complete specification line on a purchase order should read something like: “Calcium silicate insulation board, LG-Standard grade, 600 x 300 x 50 mm, density 230 kg/m³ nominal, temperature rating 1000 degrees Celsius, per ASTM C533 Type II equivalent, 100% asbestos-free, quantity 500 m².” Including all parameters reduces the likelihood of receiving material that does not match the intended service conditions. The technical data sheets page on the Mingfa website lists the standard specifications for each product series.

Sources and Further Reading

• ASTM C533-17 — Standard Specification for Calcium Silicate Block and Pipe Thermal Insulation
• ASTM C165 — Standard Test Method for Measuring Compressive Properties of Thermal Insulations
• ASTM C203 — Standard Test Methods for Breaking Load and Flexural Properties of Block-Type Thermal Insulation
• ASTM C356 — Standard Test Method for Linear Shrinkage of Preformed High-Temperature Thermal Insulation Subjected to Soaking Heat
• EN 13501-1:2018 — Fire classification of construction products and building elements
• Richardson, J. W. & Taylor, J. C. (1996). “Hydrothermal Synthesis of Calcium Silicate Hydrate Insulation.” Journal of Materials Science, 31(10), 2697-2704.
• Laizhou Mingfa Insulation Materials Co., Ltd. — Product Technical Data Sheets