Technical Notes 10 - Estimating Brick Masonry
Reissued May 1997

INTRODUCTION

Except for the non-modular "Standard Brick" (3 3/4 by 2 1/4 by 8 in.) and some oversize brick (3 3/4 by 2 3/4 by 8 in.), virtually 100 per cent of the brick produced and used in the United States are sized to fit the modular system. Even the "standard" brick is available also in a modular size (nominal dimensions 4 by 2 2/3 by 8 in.). Since there is still a considerable production of non-modular brick, this revised Technical Notes includes estimating information for that size of unit in addition to modular units.

ESTIMATING PROCEDURE

Because of its simplicity and accuracy, the most widely used estimating procedure is the "wall-area" method. It consists simply of multiplying known quantities of material required per square foot by the net wall area (gross areas less areas of all openings).

Estimating material quantities is greatly simplified under the modular system. For a given nominal size, the number of modular masonry units per square foot of wall will be the same regardless of mortar joint thickness - assuming, of course, that the units are to be laid with the thickness of joint for which they are designed. There are only three standard modular joint thicknesses: 1/4 in., 3/8 in. and 1/2 in.

In contrast, the number of non-modular standard brick required per square foot of wall will vary with the thickness of the mortar joint.

In the estimating procedure, determine the net quantities of all material before adding any allowances for waste. Allowances for waste and breakage vary, but, as a general rule, at least 5 per cent should be added to the net brick quantities and 10 to 25 per cent to the net mortar quantities. Particular job conditions, or experience, may dictate different factors.

ESTIMATING TABLES

Table 1 gives net quantities of brick and mortar required to construct walls one wythe in thickness with various modular brick sizes and the two most common joint thicknesses ( 3/8 in. and 1/2 in.). Mortar quantities are for full bed and head joints.

Table 2 provides similar information for walls constructed only with non-modular brick.

1Note: Correction factors are applicable only to those brick which have lengths of twice their bed depths.

The brick and mortar quantities in Tables 1 and 2 are for running (or stack) bond which contains no headers. For bonds requiring full headers, the correction factors given in Table 3 must be applied. Also, when estimating quantities for multiwythe walls, the mortar quantities for interior vertical and/or longitudinal collar joints given in Table 4 must be added.

Table 5 contains the quantities of portland cement, hydrated lime and sand required for 1 cu ft of four types of mortar. Although ASTM Standard Specifications for Mortar for Unit Masonry (ASTM Designation C 270) permits a range of proportions for each mortar type, the quantities in Table 5 have been based on a single set of proportions for each of these types. For convenience in estimating, quantities based on both weight and volume are included in the table. Mortar is generally proportioned by volume on the job, although proportioning by weight is the more accurate method. For more complete information on mortar ingredients, proportions, properties and uses, see Technical Notes 8 Revised, "Portland Cement-Lime Mortars for Brick Masonry".

MORTAR YIELD

General. For given volumes of materials, mortar yield depends upon proportions, water content and air content. Water content will vary with sand gradation, lime and cement content, and, quite often, the judgment of the brick mason.

Mortar yield calculations are based on absolute volume. To determine yield, first obtain:

1. Unit weights and specific quantities of all materials (see Table 6).

2. Total volume of water used in mortar mix, including mixing water and the water present in the sand.

1Values for sand are not listed because they vary considerably. Obtain precise values from laboratory tests (or from supplier).

Sand. When a relatively small amount of water (4 to 10 per cent) is added to dry sand, it bulks, that is, it increases in volume far in excess of the volume of water added. This increase can be as much as 50 per cent, depending largely upon the gradation of the sand. Because of bulking, volumetric measurement of sand is not very accurate.

Although weighing sand is a more accurate method of measurement, it is, perhaps, not nearly so convenient as measuring volume. For proportion specifications, ASTM C 270 assumes that 1 cu ft of damp, loose sand (bulked sand) is equal to 80 lb of dry sand (and that it has bulked approximately 38 per cent).

Specific Gravity of Sand. Obtain the specific gravity of sand from the supplier. Procedure for determining specific gravities of sands is given in ASTM C 128, Standard Method of Test for Specific Gravity and Absorption of Fine Aggregate. An average value for silica sands is 2.65.

Moisture Content of Sand. In any given sand, the moisture content may vary from day to day or even from hour to hour. While this variation exists, it is not as critical in mortars as it is in portland cement concrete. Most damp loose sands contain approximately 1/2 to 1 gal of water per cu ft of sand. For many yield calculations, an assumption of this amount of water may be sufficient. Where greater accuracy is desired, determine moisture content according to the procedure given in ASTM C 70, Standard Method of Test for Surface Moisture in Fine Aggregate.

Weight of Sand. To accurately determine mortar yield requires knowledge of the sand's moisture content, specific gravity and unit weight (bulked and dry). To determine bulked unit weight, weigh 1 cu ft of bulked sand. The standard method for determining unit weight of aggregate is given in ASTM C 29, Standard Method of Test for Unit Weight of Aggregate. When moisture content and bulked weight are known, the weights of water and dry sand are easily computed.

Water. Use the total weight of water in yield calculations; i.e., sum of the weights of mixing water and water present in the sand. If the moisture content of the sand is known, it is a simple matter to calculate the weight of water in the sand. Add the weight of water present in the sand to the weight of mixing water added to the batch at the mixer. To convert gallons of mixing water to pounds, multiply by 8.33.

Absolute Volume. The absolute solid volume of a material is the volume of its solid portion only; voids are not included. Thus:

Vm = absolute solid volume of any given material in cubic feet

Wm = batch weight of the material in pounds

Gm = specific gravity of the material

Y = volume of mortar yield in cubic feet

VM = absolute solid volume of mortar in cubic feet from Eq (2)

a = air content of freshly mixed mortar in per cent

Mortar Yield by "Rule-of-Thumb". For jobs where mortar yield calculations are not critical, use the following "rule-of-thumb" to determine approximate mortar yield:

For each 1 cu ft of damp loose sand, the mortar yield will be 1 cu ft.

Illustrative Example. Determine the batch yield for the following mortar:

Batch proportions by volume: 1 cu ft portland cement, 1 cu ft lime, 6 cu ft damp loose sand, and 8 1/3, gal mixing water. For all materials except sand, specific gravities and unit weights are as shown in Table 6. Specific gravity of sand, GS = 2.65. Moisture content of sand, w = 8 per cent. Damp loose weight of sand, W = 87 lb per cu ft. Batch weight of sand = 6(87) = 522 lb. Assume mixed mortar contains 10 per cent air.

Step1. Determine the total weight of each material in the batch (see Table 6).

Step 2. Using the batch weights determined in Step 1, calculate the absolute solid volume for each material from Eq (1) and the total from Eq (2)
Step 3. Determine mortar yield from Eq (3)

Note: By the "rule-of-thumb" method the yield is 6 cu ft. However, had this mix required more or less mixing water, or had it varied in air content, the yield would have varied also. Conceivably, this difference may be significant for large quantity computations.