Refractory Bricks: Types, Compositions, Properties and How to Choose

Refractory bricks are shaped refractory products, fired, chemically bonded, carbon-bonded or fused-cast, that line kilns, furnaces, ladles and reactors, and they fall into 15 classes from fireclay brick to carbon blocks. Which class fits a zone depends on chemistry, temperature and slag, so how are the classes told apart?

A refractory fire brick, a refractories brick and refractory brickwork all name one product family: shapes of fixed size, laid with mortar or dry into a lining. Shaped bricks are one of three forms of refractory materials, next to monolithics and insulation.

The 15 classes sort into five groups. ISO 836:2001 sets the chemistry boundaries, ASTM C27-98(2022), C416-97(2022) and C455-07(2022) add the US classes and scope limits, and ISO 10081 splits basic brick at 7 % residual carbon. Seven industries take different classes zone by zone, and cutting or tearing out brick falls under the OSHA respirable crystalline silica limit of 50 µg/m³ (29 CFR 1910.1053, effective 2016-06-23).

Every value names its standard and edition, the product data sheet or the dated source it comes from; see our methodology and fact-checking process.

What Is a Refractory Brick?#

A refractory brick is the shaped form of a refractory, which ISO 836:2001 (term 107) defines as a non-metallic material or product whose chemical and physical properties allow it to be used in a high temperature environment. The ISO term carries no temperature threshold; ASTM C71-12(2024) sets the US boundary at 538 °C (1,000 °F).

Refractory bricks are the shaped form, made to fixed dimensions before they reach the site. Monolithic refractories, such as castables, gunning mixes and ramming mixes, take their final form in place. Refractory insulation, such as insulating firebrick, fiber and microporous board, sits behind the working lining and limits heat flow.

What Are Refractory Bricks Made Of?#

Refractory bricks are made of coarse refractory grains, a bond phase and small additions that adjust firing, oxidation or wetting. The main oxide or carbon content names the class: Al2O3 in fireclay and high-alumina brick, SiO2 in silica brick, MgO in magnesia brick, carbon in carbon blocks. Refractory raw materials for these classes include bauxite, andalusite, mullite, magnesia, chrome ore, zircon, silicon carbide and graphite.

Fireclay brick is rarely made from one raw clay: producers blend clays and add grog, according to a peer-reviewed review by Garbers-Craig (Journal of the SAIMM, 2008). Each grain is covered under refractory raw materials.

Fired, Chemically Bonded, Carbon-Bonded and Fused-Cast Bricks#

Refractory bricks follow one of four bond routes: ceramic (sintered above 800 °C, 1,472 °F), inorganic chemical (formed below 800 °C), carbon (from resin or pitch) or fusion casting. ISO 10081-1:2003 defines the ceramic, chemical and fusion-cast bond types and names a raw material in the designation when it makes up 50 % or more. The carbon bond forms when resin or pitch cokes.

ISO 10081-1:2003 excludes products with more than 5 % of a metallic oxide other than Al2O3, SiO2 and iron oxide, or more than 1 % carbon, carbides, nitrides or oxynitrides; those move to Parts 2, 3 or 4.

Types of Refractory Bricks: 15 Classes and the Size Series#

There are 15 types of refractory brick in five groups (alumina-silica, basic, carbon-containing, special and functional shapes), and a 16th entry covers the size and shape series that applies to all of them. Table 1 lists each class with its character, defining chemistry and basis, bond, US and ISO standard and main lining zones.

Character after ISO 836:2001; neutral is a practical label. Rows 1 to 15 are brick classes; row 16 is the size series that applies to every class.

Alumina-Silica Bricks: Fireclay, High-Alumina and Silica#

Alumina-silica bricks are the acid and neutral workhorses: fireclay for moderate zones, high-alumina where temperature or aluminum contact rises, silica for crowns and coke oven walls. Phosphate-bonded high-alumina grades face molten aluminum in melting and holding furnaces.

ASTM C27-98(2022) classifies fireclay brick by physical properties and high-alumina brick by Al2O3 content; mullite brick has its own classification in ASTM C467-14(2023). The chemistry boundaries of all three families sit once, in Table 2.

Basic Bricks: Magnesia, Magnesia-Chrome, Magnesia-Spinel and Dolomite#

Basic bricks resist lime-rich slags and are grouped in ISO 10081-2:2003 by MgO content: M (magnesia), MCr (magnesia-chromite), MSp (magnesia spinel) and D (dolomite) types. Magnesia brick lines BOF permanent linings, electric arc furnaces, lime kilns and glass furnaces, while dolomite brick lines AOD and VOD converters and ladles. Dolomite brick takes only anhydrous binders and mortars, because its free CaO hydrates in contact with water.

Magnesia-chrome brick remains the class for RH degassers and for copper converters and smelters. In cement kilns, chrome reacts with lime and alkali to hexavalent chromium, which drove the change to chrome-free magnesia-spinel brick in the burning and transition zones.

Carbon-Containing Bricks: Magnesia-Carbon, AMC and Carbon Blocks#

Carbon-containing bricks combine an oxide grain or carbon with a coked binder: magnesia-carbon brick holds 7 % to below 50 % residual carbon under ISO 10081-3:2003, and carbon blocks fall under ISO 10081-4:2014. Magnesia-carbon brick lines BOFs, electric arc furnaces and ladle slag lines.

Alumina-magnesia-carbon (AMC) brick lines ladle barrels and bottoms and torpedo ladles. Its resin bond is tempered, and above about 1000 °C (1,832 °F) in-situ spinel forms with an expansion that tightens the joints. Carbon blocks and graphite bricks line the blast furnace hearth wall and bottom.

Special Shapes: Zircon, Fused-Cast AZS and Silicon Carbide#

Special shapes are the zircon, zirconia, fused-cast AZS and silicon carbide products that ISO 10081-4:2014 classifies outside the alumina-silica and basic parts. Zircon and zirconia bricks pave E-glass and borosilicate furnace bottoms. Fused-cast AZS falls into ISO groups such as AZS30/30 (30 to below 40 % ZrO2) and AZS30/40 (40 to below 50 % ZrO2), both above 30 and up to 55 % Al2O3; AZS 33, 36 and 41 are trade grades, not ISO groups.

Silicon carbide brick is classed by bond type, and ASTM C863-00(2022) tests its oxidation resistance in steam.

Functional Shapes: Flow Control, Checkerwork and Size Series#

Functional shapes are defined by their job, not their chemistry: flow control refractories meter and shroud liquid steel, and checker bricks store and release heat in regenerators and hot blast stoves. Flow control parts are cold isostatically pressed and fired in a non-oxidizing atmosphere. Burner blocks and other precast refractory shapes are cast from castable, not pressed; see precast refractory shapes.

The size series applies to every class: ASTM C909-18(2022) builds US shapes on a 38 mm (1-1/2 in) module, and ISO 5019-1:1984 sets squares of 230 × 114 × 64 and 76 mm (9.06 × 4.49 × 2.52 and 2.99 in).

How Are Refractory Bricks Classified by Chemistry and Standard?#

Refractory bricks are classified by main oxide or carbon content, by the ASTM classification that names the US class and by the ISO 10081 part that groups them; acid, neutral and basic describe slag compatibility, not a standard class. A purchase specification names all three: chemistry with its basis, the ASTM class and the ISO 10081 group.

ISO 836:2001 defines acid, basic and neutral refractories by reaction: acid ones contain substantial silica and react with basic slags, basic ones (magnesia, CaO, chromite, spinel, forsterite) react with acid slags, and neutral ones show no appreciable reaction. Class by class, see acid, basic and neutral refractories.

Chemistry Thresholds in ASTM and ISO Side by Side#

ISO 836:2001 fixes the chemistry boundaries between families; ASTM C27-98(2022) and C416-97(2022) add class requirements and scope limits. Table 2 sets the ISO definition or group next to the US classification for six brick families.

All chemistry in mass %; ISO 10081 groups are analyzed on the calcined product.

ASTM C27-98(2022) grades fireclay brick by physical properties, because the Al2O3 and SiO2 contents of its super duty, high duty, medium duty, low duty and semi-silica classes overlap; it states inch-pound units as standard.

ASTM C416-97(2022) applies only to silica brick inside every scope limit, so a brick with 1.50 % Al2O3 falls outside it. The ASTM C27 classification, class by class, is set out under ASTM C27 classification of fireclay and high-alumina brick.

Residual Carbon and the Four Parts of ISO 10081#

ISO 10081 splits dense shaped refractory products into four parts by chemistry and residual carbon, with the 7 % residual carbon line separating Part 2 from Part 3. All four parts were confirmed by ISO on 2025-06-10.

Part 3 groups magnesia-carbon brick by MgO in steps of 98, 95, 90, 85 and 80 % and by residual carbon in bands from 7 to below 10 % up to 30 to below 50 %; MC 85/10A is a magnesia carbon designation with antioxidants.

The ISO 10081 classification of dense shaped products measures residual carbon after coking to ISO 10060:1993; ASTM C831-18(2023) does not separate carbon in SiC from free carbon. See ISO 10081 classification of dense shaped products.

Which Refractory Brick Suits Which Temperature, Slag and Atmosphere?#

The right refractory brick is the class whose chemistry matches the zone's slag and atmosphere: silica or fireclay for acid service, magnesia-based brick for basic slag, carbon-containing brick where slag and thermal shock combine. Temperature comes next, through standard test results at the zone's service temperature. A specification should name the standard and class, not a brand.

Selection runs zone by zone, not furnace by furnace. A steel ladle takes magnesia-carbon brick in the slag line and AMC brick in the barrel and bottom, and a cement kiln takes magnesia-spinel brick in the burning and transition zones but high-alumina brick in the preheater and cooler.

Brick Classes by Industry and Lining Zone#

Seven industries consume the brick classes, and each lining zone takes a different class, as Table 3 shows.

Steel takes ten of the classes in Table 3, from carbon blocks in the blast furnace hearth to flow control parts at the tundish, where liquid steel runs at about 1500 to 1570 °C (2,732 to 2,858 °F) (Nippon Steel Technical Report No. 125, 2020).

Slag Chemistry, Alkalis and Reducing Atmospheres#

Slag chemistry decides between acid and basic brick, because silica-rich brick reacts with basic slags and magnesia brick with acid slags at service temperature (ISO 836:2001). High-alumina, AZS, zircon, SiC and carbon classes carry the neutral label in Table 1, a practical label for products with no appreciable reaction with acid or basic slag.

Atmosphere changes the choice for carbon-bearing classes. Carbon-containing brick loses graphite in oxidizing service, so antioxidant powders protect it, and a silica-rich glaze seals flow control graphite against air during preheat. Used magnesia-chrome brick from alkali-rich oxidizing service can carry water-soluble hexavalent chromium. These are forms of slag and chemical attack, covered under slag and chemical attack.

High-Temperature Limits: Test Results Versus Producer Ratings#

A high-temperature refractory brick is defined by standard test results, PCE to ASTM C24-09(2022) and reheat change to ASTM C113-14(2025), not by a producer's service rating. ASTM C27-98(2022) grades fireclay brick by these results and modulus of rupture to ASTM C133-24, so a duty class is a test outcome. ASTM C24-09(2022) applies PCE as a specification value only to fireclay and high-alumina materials.

Under load, creep and refractoriness under load decide: high-alumina brick for hot blast stoves and reheat furnaces is chosen on creep and RUL at 1000 to 1500 °C (1,832 to 2,732 °F) (Journal of the SAIMM, 2013). A producer's service temperature is a product claim for the class page.

Binders and Additives in Refractory Bricks#

Every refractory brick class depends on a bond phase and small additions: clay or lime in fired alumina-silica brick, phosphate in chemically bonded high-alumina, resin and antioxidants in carbon-containing brick, spinel in chrome-free basic brick. Fused-cast AZS replaces the bond with a soda-bearing glassy phase. Table 4 lists the bond and main additions of nine brick groups, with level and basis.

Levels in Table 4 are standard limits or class ranges from published reviews and papers, not product recipes. Refractory additives and binders beyond brick, such as calcium aluminate cement, dispersants and fibers, are covered under refractory additives and binders.

Clay, Lime and Phosphate Bonds in Fired and Chemically Bonded Bricks#

Fired alumina-silica bricks are bonded by clay or lime, and chemically bonded high-alumina bricks by phosphate. Silica brick uses a lime bond: lime reacts with fine silica to beta-dicalcium silicate above 600 °C (1,112 °F), converting near 1000 °C (1,832 °F) to pseudo-wollastonite, and the melt mineralizes quartz to tridymite and cristobalite (Engel, Glass International, 2019). A lignosulfonate solution serves as pressing aid.

Phosphate-bonded high-alumina brick uses phosphoric acid or aluminum phosphate and is supplied cured or burned. ISO 10081-1:2003 records the bond in the designation, as in "HA 75 based on natural calcined bauxite and sillimanite, chemical inorganic bond, tempered".

Resin, Pitch and Antioxidants in Carbon-Containing Bricks#

Carbon-containing bricks are bonded by phenolic resin tempered at about 200 °C (392 °F) or by coal tar pitch. The resin is a novolac with hexamethylenetetramine hardener or a resol; pitch releases polyaromatic volatiles and falls under the CTPHT rules in the handling section.

Converter grades of magnesia-carbon brick carry 15 to 20 mass % graphite (Nippon Steel Technical Report No. 125, 2020). Antioxidants for carbon-containing refractories include aluminum, silicon, Al-Mg alloy, B4C, CaB6 and SiC; see antioxidants for carbon-containing refractories.

Aluminum powder forms Al4C3 and AlN, then Al2O3 and MgAl2O4 spinel above about 1000 °C (1,832 °F), raising hot modulus of rupture.

Spinel, Soda and Nitride Bonds in Basic and Special Bricks#

Spinel, a soda-bearing glass and nitride phases bond three classes: magnesia-spinel brick, fused-cast AZS and silicon carbide brick. Magnesia-spinel brick contains 10 to 20 % spinel, a class range stated in a UNITECR 2025 conference paper, added preformed (sintered or fused) or formed in situ from calcined alumina. The expansion mismatch between MgO and spinel creates microcracks that raise thermal shock resistance.

Fused-cast AZS is melted from alumina, zircon sand, soda ash and recycled AZS in an electric arc furnace at about 2200 to 2400 °C (3,992 to 4,352 °F) (van Dijk, Eindhoven University of Technology, 1994). Soda forms the glassy phase that absorbs the zirconia volume change at 900 to 1200 °C (1,652 to 2,192 °F). Silicon carbide brick bonds through oxide, Si3N4, Si2N2O or beta-SiAlON phases, or self-bonds.

Standards and Test Methods for Refractory Brick Data Sheets#

Refractory brick standards come in two layers: classifications that define the classes and test methods that produce the data-sheet values. The classification layer covers ASTM C27-98(2022), C416-97(2022), C455-07(2022), C467-14(2023) and C1547-02(2022) and ISO 10081 Parts 1 to 4; the test layer covers ASTM C20-00(2022), C133-24, C113-14(2025) and C24-09(2022) with their ISO counterparts.

Side by side means the same family or the same property, never equivalent requirements: a value measured to one method is reported with that method's designation and edition. The full list of refractory standards with editions, ASTM, ISO, EN and API, is kept under refractory standards.

Classification Standards by Brick Family#

Five brick families map to US and ISO classifications, and Table 5 lists them with their EN adoptions.

ASTM C455-07(2022) covers machine-made chrome, chrome-magnesia, magnesia-chrome and magnesia brick and classes them by MgO, except chrome brick. It excludes electrofused magnesia and fusion-cast products; ASTM C1547-02(2022) classifies fusion-cast blocks and shapes by mineralogical composition and excludes fused grains, and ASTM C1223-19(2023) measures the glass exudation of fusion-cast AZS as a percentage volume increase.

Test Methods Behind Brick Property Values#

Five property tests stand behind brick data sheets: porosity and bulk density, cold crushing strength, modulus of rupture, permanent linear change and refractoriness, plus the hot load test. Table 6 pairs each ASTM method with its ISO or EN method for the same property; what each value means is explained under properties of refractory materials.

Two European methods changed in 2025: EN ISO 10059-1:2025 (cold crushing strength) and EN ISO 5014:2025 (modulus of rupture at ambient temperature) replaced their EN 993 parts on 2025-12-09, so a data sheet citing EN 993-5 or EN 993-6 uses a superseded method. ISO 2478:2025 excludes carbon-containing products.

Sourcing, Installing and Handling Refractory Bricks#

Sourcing refractory bricks starts with a specification that names class and standard, continues with a lining laid in matching mortar and heated on a controlled schedule, and ends with dust and waste rules for cutting and tear-out. Each step has its own document: a classification standard for the order, a brick lining standard for installation and occupational exposure limits for the work.

Bricklaying is one of the refractory installation methods, next to casting, pumping, gunning and shotcrete. Method by method, the steps are covered under refractory installation methods.

What a Refractory Brick Specification and RFQ Contain#

A refractory brick specification names class and standard, chemistry target with basis, shape series, key properties (bulk density, porosity, cold crushing strength, hot MOR, permanent linear change) and quantity in metric tonnes (a US short ton is 907.2 kg). The four US tariff lines below cover refractory bricks, blocks and other refractory ceramic goods (hts.usitc.gov, checked 2026-10-27).

• 6902.10: more than 50 % MgO, CaO or Cr2O3
• 6902.20: more than 50 % alumina, silica or a mixture of these
• 6902.90: other refractory bricks, blocks and tiles
• 6903.10: other refractory ceramic goods with more than 50 % free carbon

Refractory mortars fall under heading 3816. Quote factors are class, raw-material origin, shape complexity, quantity, freight and trade-remedy duties (US antidumping orders on certain magnesia-carbon bricks from China and Mexico since September 2010, third five-year review instituted 2026-07-01). The US BLS producer price index for clay refractories (WPU1352, 1982 = 100) stood at 405.818 in September 2026, a trend, not a price.

Bricklaying, Mortar Joints and Heat-Up of Brick Linings#

A brick lining is laid in a refractory mortar of matching chemistry, fireclay or high-alumina, air-setting or heat-setting, with a larger expansion allowance for high-alumina than for fireclay brick. Joints stay thin, and mortar types by setting mechanism are covered under refractory mortar.

Brick rings in a steel shell hold by interference fit, so start-up and shutdown after the initial dry-out run at no more than 56 to 69 °C/h (100 to 125 °F/h) (Thorpe, cited by Jenkins, 2011). API Std 975, 2nd edition (April 2025), covers brick systems.

Crystalline Silica, Chromium and Pitch Rules for Brick Work#

Cutting and tearing out brick releases respirable crystalline silica, which OSHA limits to 50 µg/m³ as an 8-hour TWA with an action level of 25 µg/m³ (29 CFR 1910.1053, construction 29 CFR 1926.1153, effective 2016-06-23). The EU limit is 0.1 mg/m³, respirable fraction (Directive (EU) 2017/2398, transposition by 2020-01-17). For quartz (crystalline silica), ECHA (read 2026-10-27) gives: "No Annex VI entry; product-specific, see supplier SDS (ECHA C&L: no majority; not classified 27.5 %, H372 25.2 %, H373 18.8 %, H350 7.7 %)".

Used magnesia-chrome brick can carry hexavalent chromium: OSHA PEL 5 µg/m³, action level 2.5 µg/m³ (29 CFR 1910.1026, eCFR text of 2026-10-27); EU limit 0.005 mg/m³ since 2025-01-18 (Directive (EU) 2017/2398).

Coal tar pitch, high temperature (CTPHT, CAS 65996-93-2) carries "Harmonised CLP Annex VI: H340, H350, H360FD" (index 648-055-00-5, Delegated Regulation (EU) 2020/217) and is REACH Annex XIV entry 41, sunset 2020-10-04 (Commission Regulation (EU) 2017/999), so EU use after that date needs an authorization. Each hazard has its own page, listed below.

• crystalline silica in refractories: silica phases, exposure limits and silica brick work
• hexavalent chromium in spent magnesia chrome refractories: Cr(VI) formation in used brick
• coal tar pitch in carbon-bonded refractories: CTPHT, PAH and resin fumes

How Do Refractory Bricks Compare With Other Lining Materials?#

Refractory bricks compete with castables, insulating firebrick and fiber: brick brings factory-set properties and fixed dimensions, castables bring jointless linings, insulating products bring low conductivity behind the working lining. In everyday use, "fire brick" means one class of refractory brick, fireclay brick, so every fire brick is a refractory brick but not every refractory brick is a fire brick. The difference between fire brick and refractory brick is answered under fireclay brick.

Residential firebox and pizza-oven bricks are consumer products outside the scope of this page. Insulating firebrick is a shaped insulating product, not a dense refractory brick, and belongs with refractory insulation.

How Long Do Refractory Brick Linings Last?#

Refractory brick lining life is counted in heats for steel vessels and in months or years for continuous furnaces; Si3N4-bonded SiC sidewalls in aluminum reduction cells last campaigns of 60 to 84 months (ICSOBA, 2023).

The same zone can be lined with brick or castable, and lining life is one criterion; see castable vs refractory brick.

Do Fired Bricks Need a Dry-Out Before Service?#

Fired bricks hold no mixing water and need no curing, so the heat-up follows the producer's schedule and the castable and mortar around them. Resin-bonded magnesia-carbon brick holds no water either, but aluminum-bearing grades must stay dry before heat-up, because Al4C3 hydrates.