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Technical Notes 9A - Manufacturing, Classification, and Selection of Brick
Abstract: This Technical Notes describes the various kinds of brick and their classification. Specific requirements including physical properties, efflorescence, dimensional tolerances, distortion, chippage, and coring are described. Additional requirements for each kind of brick are also covered.

Key Words: appearance, ASTM Standards, brick, chippage, classification, cores, dimensional tolerances, distortion, efflorescence, exposure, frogs, grades, physical properties, types, uses.

The classification of brick is determined by the usage of brick in specific applications. Brick used in the wrong application can lead to failure or an unpleasing appearance. Standard specifications have been developed to produce uniform requirements for brick. The standard specifications include strength, durability and aesthetic requirements.

The American Society for Testing and Materials (ASTM) publish the most widely accepted standards on brick. These standards are voluntary consensus standards. All have been through a review process by various segments of the construction industry - producers, users and general interest members. Most of the model building codes reference ASTM standards. Many of the requirements in the brick standards aid in predicting the durability of the product in actual use. These predictors, and other requirements in ASTM standards, are not infallible. All ASTM standards are reviewed and updated periodically to obtain optimal performance.

This Technical Notes addresses the specific requirements for various classifications of brick. Other Technical Notes in this series provide the fundamentals of brick manufacturing and the proper selection of brick.

Fig. 1

Depending on its use, brick can be classified by one of several specifications.

1American Society for Testng and Materials, 100 Barr Harbor Drive, West Conshoohocken, PA 19428-2959

2Canadian Standards Association, 178 Rexdale boulevard, Etibicoke, Ontario, Canada, M9W 1R3

Since chemical resistant brick and industrial floor brick are special applications, they will not be addressed in this Technical Notes.

As the names imply, the uses of brick are similar to their respective ASTM designations.

Building Brick. Building brick are intended for use in both structural and non-structural masonry where appearance is not a requirement. Building brick are typically used as a backing material.

Facing Brick. Facing brick are intended for use in both structural and non-structural masonry where appearance is a requirement.

Hollow Brick. Hollow brick are identical to facing brick but have a larger core area. Most hollow brick are used in the same application as facing brick. Hollow brick with very large cores are used in walls that are reinforced with steel and grouted solid. Larger cores or cells in hollow brick allow reinforcing steel and grout to be placed in these units whereas it would be difficult to do so with building brick, facing brick or some hollow brick.

Paving Brick. Paving brick are intended for use as a paving material to support pedestrian and light vehicular traffic.

Ceramic Glazed Brick. Ceramic glazed brick are units with a ceramic glaze fused to the body and used as facing brick. The body may be either facing brick or other solid masonry units.

Thin Brick. Thin brick veneer units are fired clay units with normal face dimensions, but a reduced thickness. They are used in adhered veneer applications.

Sewer and Manhole Brick. Sewer and manhole brick are intended for use in drainage structures for the conveyance of sewage, industrial wastes, and storm water; and related structures, such as manholes and catch basins.

There are several terms in each standard used for classification which may include exposure, appearance, physical properties, efflorescence, dimensional tolerances, distortion, chippage, cores and frogs. Brick can be classified by use, grade, type and/or class in most specifications. All options should be specified, as each ASTM brick standard has requirements for grade and type which apply automatically if an option is omitted. By not specifying the desired requirements, a delivery may contain brick not suitable for the intended use.


Because of the varying climates throughout the country, and the different applications of brick, specific grades of brick are required. Brick must meet a grade of SW, MW, or NW based on the weathering index and the exposure of the brick. The weathering index is the product of the average annual number of freezing cycle days and the average annual winter rainfall in inches (see Figure 1). The exposure is related to either a vertical or horizontal surface and whether the unit will be in contact with the earth (see Table 1). A higher weathering index or a more severe exposure will require a face brick to meet the SW requirements. The grade is typically based on physical properties of the brick. See Technical Notes 9B for selection of grades. The grades for each specification are listed in Table 2, and the physical requirements are listed in Table 4.

Brick types are related to the appearance of the unit, and specifically to limits on dimensional tolerances, distortion tolerances and chippage of the units. The brick type can be selected depending upon whether: a high degree of precision is necessary; a wider range of color or size is permitted; or a characteristic architectural effect is desired. The types of brick for each specification are listed in Table 3, and requirements for size variation, distortion, and chippage are listed in Tables 5, 6 and 7, respectively.

1No requirements for durability

2Based on durability and abrasion

Physical Property Requirements
The physical property requirements in most specifications are compressive strength, water absorption and saturation coefficient. These properties must be determined in accordance with ASTM C 67, Standard Methods of Sampling and Testing Brick and Structural Clay Tile. The minimum compressive strength, maximum water absorption and maximum saturation coefficient are used in combination to predict the durability of the units in use. The saturation coefficient, also referred to as the C/B ratio, is the ratio of 24 hour cold water absorption to the 5 hour boiling absorption. The physical property requirements for each standard are listed in Table 4.

1Hollow brick in bearing position.

2Numbers in parentheses are for molded brick and apply provided the requirements for saturation coefficient are met.

3Where a high and uniform degree of resistance to frost action in the presence of moisture is required. See C 32 for waiver of saturation coefficient.

Alternates. Because of the variability of raw materials and production methods throughout the country, it is difficult to use only these requirements to classify all brick. Therefore, in each standard there are waivers which include those brick which are durable but cannot be classified under the physical requirements. Using the waiver permits the use of brick which are known to perform well. It does not signify that the brick are of a lower quality. Waivers include: waiving the saturation coefficient and water absorption requirements if brick are intended to be used where the weathering index is less than 50; waiving the saturation coefficient requirement if the cold water absorption is less than 8% on an average of five units allowing one brick of the sample to exceed 8% but be less than 10%; waiving the saturation coefficient and water absorption requirements if the sample complies with the 50 cycle freeze and thaw test requiring no breakage and not greater than 0.5% loss in dry weight of any individual brick (Grade SW only). Freeze-thaw requirements apply only if the units do not meet the saturation coefficient and absorption requirements. For waivers specific to each type of brick, consult the appropriate ASTM Specification.


Efflorescence is a crystalline deposit of water-soluble salts which forms on the surface of masonry. The principal objection is an unsightly appearance, though it typically is not harmful to brick. The test for efflorescence is described in ASTM C 67. The brick is given a rating of "effloresced" or "not effloresced". ASTM standards (C 216, C 652, C 902, C 1088) require the rating for brick to be "not effloresced".

Although brick is the only material in masonry construction that is tested for efflorescence, brick itself is not a major source of efflorescing salts.

Dimensional Tolerances

Because of the variations in the raw materials and the manufacturing process, brick may vary in size. The permitted size variation is based on the brick type and the dimension being measured. These variations in size are listed in Table 5. The variation is plus or minus from the specified dimension. Generally, "through-the-body" colored brick with a wide color range will also have a wide variation in dimensions. Brick without a wide color range may vary one way or another. Size variation becomes important when constructing an assembly with units aligned vertically or in wall sections with short horizontal dimensions.


Dimensional Tolerances

1As specified by the purchase

2Over 5 in. to 8 in.

3No limit

4Special Requirements -- see ASTM C 126


Permitted distortion, or warpage, of brick is listed in Table 6. The amount of distortion is based on the brick type and face dimension. Other terms for distortion are "bowed" or "banana" brick. A brick that is over the distortion limitations is difficult to lay and is easily noticeable in the finished wall.

1As specified by the purchaser

2Special requirements - see ASTM C 126


Brick may be damaged or chipped during packaging, shipping or on the jobsite. Limitations to the size and number of chips on individual units are listed in Table 7. The amount of chippage is based upon the brick type.

A delivery of brick may contain up to 5% broken or chipped brick beyond the limits in Table 7. The chippage requirements in Table 7 are based on the remaining 95% of the shipment. The chips are measured from an edge or a corner, and the total length of these chips may not be greater than 10% of the perimeter of the face of the brick. Chips are more noticeable on brick that have a surface color different from the body of the brick. Chips on "through-the-body" color brick are less noticeable.


Maximum Permissible Range of Chippage1

1There are no chippage requirements for C 62, or C 32.

2Smooth texture -- die skin finish.

3Rough texture - sanded, combed, scratched, wire cut.

Brick are generally classified as solid or hollow. A solid brick unit is defined as a unit whose net cross-sectional area in every plane parallel to the bearing surface is 75% or more of its gross cross-sectional area measured in the same plane. Thus, a solid brick unit has a maximum coring of 25%. A hollow brick unit is defined as a unit whose net cross-sectional area in every plane parallel to the bearing surface is less than 75% of its gross cross-sectional area measured in the same plane. A hollow brick unit has a minimum coring of 25%, and a maximum coring of 60%.

Holes in brick, referred to as cores, are used to aid in the manufacturing process and shipping of brick. The cores create more uniform drying and firing of the units, reduce the amount of fuel necessary to fire the units and reduce shipping costs by reducing weight. Additional advantages, such as aiding in mechanical bond in a wall, easier laying of the units, etc., may also result from brick manufactured with cores. Cores are only found in brick manufactured by the extrusion or dry-press process. Limits to the amount of coring allowed in brick, the distance from a core to a face, and web thickness where applicable are listed in Table 8.

Cells are similar to cores except that a cell is larger in cross-section than a core. Some requirements for cells are shown in Table 8. Additional requirements for cells can be found in ASTM C 652 and C 126.


Frogs are depressions in brick usually located on one bed surface and are included for the same reasons as cores. Frogs are found in brick manufactured by the molded process. Panel frogs are limited to a specified depth and a specified distance from a face. Requirements for panel frogs are listed in Table 8. Deep frogs are frogs that are deeper than 3/8" (10 mm) deep, and must conform to the requirements for coring, hollow spaces and void area of the applicable standard.


Requirements for Cores and Frogs1


1Deep frogsshall meet coring requirements of the applicable standard (see ASTM C 62, C216, C 652)

2Additional coring requirments for cored-shell and double-shell hollow brick in ASTM C 652

3Based on 3" and 4" nominal width (For 6", 8", 10" and 12" see C652

4Additional Requirements for cells in ASTM C 126

5See C 126 for web thickness in cored units


Paving Brick, ASTM C 902

Not only must paving brick conform to the physical requirements in Table 4, but they must meet additional requirements for abrasion resistance or alternate performance requirements.

Alternate Performance Requirements. If information on the performance of units in an application of similar exposure and similar traffic is given, then the physical requirements in Table 4 may be waived.

Paving brick manufactured by the molded process have different physical requirements. See Table 4.

An optional test for the freeze and thaw test is ASTM C 88 Test Method for Soundness of Aggregates by Use of Sodium Sulfate. The sulfate soundness test, like the freeze/thaw test is not required, and the requirements apply only if the paving units do not meet the saturation coefficient and absorption requirements.

Abrasion Requirements. Since paving brick are used in a horizontal application and are exposed to traffic, brick must meet a specified abrasion limit. Paving brick are assigned a type by the traffic or abrasion expected. Type I pavers are exposed to extensive abrasion, such as driveways or public entries. Type II pavers are exposed to high levels of pedestrian traffic, such as in stores, restaurant floors or exterior walkways. Type III pavers, are exposed to pedestrian traffic, such as floors or patios in homes. The abrasion resistance can be determined in either of two ways: 1) an abrasion index is calculated by dividing the absorption by the compressive strength and multiplying by 100, or 2) by determining the volume abrasion loss in accordance with ASTM C 418 Test Method for Abrasion Resistance of Concrete by Sandblasting. The abrasion requirements for Type I, II, and III are listed in Table 9.

Ceramic Glazed Brick, ASTM C 126

Since this specification is for ceramic glazed brick and tile, there are requirements for properties of the finish. These are imperviousness, opacity, resistance to fading, resistance to crazing, flame spread, fuel contribution and smoke density, toxic fumes, hardness and abrasion resistance. Requirements for each of these are included in the specification.


This Technical Notes describes the classification of brick and the specific requirements found in ASTM standard specifications. It attempts to clarify some of the wording in ASTM specifications, although an official interpretation from ASTM must be received from the appropriate subcommittee. Problems and confusion can be eliminated if a basic understanding of the ASTM specifications is known.

The information and suggestions contained in this Technical Notes are based on the available data and the experience of the technical staff of the Brick Institute of America. The information contained herein should be used with good technical judgment and an understanding of the properties of brick masonry. Final decisions on the use of the information discussed in this Technical Notes are not within the purview of the Brick Institute of America and must rest with the project designer, owner or both.

More detailed information on subjects discussed here can be found in the following publications:

1. ASTM Standard Specifications for Brick, Mortar and Applicable Testing Methods for Units Reprinted by the Brick Institute of America.

2. ASTM C 88 Test Method for Soundness of Aggregates by Use of Sodium Sulfate. Annual Book of ASTM Standards, Volume 04.02.

3. ASTM C 418 Test Method for Abrasion Resistance of Concrete by Sandblasting. Annual Book of ASTM Standards, Volume 04.02.

4. Technical Notes on Brick Construction 9B, "Manufacturing, Classification and Selection of Brick - Selection - Part III of III", January 1989.

4. American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshocken, PA 19428-2959" and "Canadian Standards Association, 178 Rexdale Boulevard, Etibicoke, Ontario, Canada, M9W 1R3

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