Masonry Magazine October 1989 Page. 22
MATERIALS
Units
Concrete masonry units are designated by their nominal dimensions: width, height, and length (in that order) and are included under one of the following product specifications: ASTM C90, ASTM C145, ASTM C129, ASTM C55. Modular unit dimensions are actually 3/8 inch less than stated to allow for the thickness of the mortar joint.
Field inspection of masonry units includes determining that units are sound and free of cracks or other defects that would interfere with the proper placing of the unit or impair the strength or permanence of the construction. Minor imperfections are not grounds for rejection unless clearly stated in the specification. Units selected at the job site for laboratory testing should be picked at random so that the sample is representative. Concrete masonry units on the job site should be protected against wetting prior to use. Preferably they should be stored off the ground as moisture can be absorbed from the ground as well as from rain or snow. Once wetted, units at the job site will dry to equilibrium with the atmospheric conditions if sufficient time is permitted and units are protected from further exposure to moisture.
Aggregates for Mortar and Grout
Aggregates meeting the specification requirements should be delivered to the job site pretested so that checks need only be made to insure that the gradations are consistent. Field tests are necessary only when required by the job specifications. Aggregates are to be stored in a dry, level location from which they can be protected from deleterious substances.
When the color of mortar joints is critical, aggregates must be obtained from the same source. If possible, sufficient aggregates required for those portions of the job where control of color is critical should be stockpiled at one time.
Cementitious Materials
Cementitious materials such as portland cement (ASTM C150), masonry cement (ASTM C91) and lime (ASTM C207) should be stored off the ground and protected from moisture.
When the color of mortar joints is critical, the same type and brand of material should be used throughout the job.
Any sacks containing hard lumps should be rejected.
Reinforcing Steel
Reinforcing steel must be stored to keep it free from dirt, mud, oil or any other foreign substance detrimental to bond and protected from kinking or bending. Moderate amounts of surface rust or mill scale are usually not considered to be detrimental to bond.
MATERIAL PREPARATION
Mortar
Proportions for the various types of mortar are regulated by ASTM C270.
Once the mortar proportions are established, it is important they be accurately and consistently maintained for the duration of the project. Batch size should be such that cement can be used in full sack quantities. Sand should be accurately measured, preferably in a box constructed to contain a volume of one cubic foot.
Mortar should be mixed in a paddle type mechanical mixer. The desirable sequence of mixing consists of loading approximately one-half of the sand and water into the operating mixer; next all the cementitious materials are added; and then the remainder of the sand and water are added. Mixing should continue for a minimum of 3 minutes after all materials had been added. Admixtures should not be used without permission of the designer.
The inspector does not have the authority to change the mortar from that specified; however, he should reject a mortar which is unworkable and consult with the engineer or architect to find a solution.
Grout
Grout for use in concrete masonry should comply with ASTM C476. Fine or coarse grout may be used depending upon the horizontal dimension of the grout space; fine grout is used when the minimal dimension is 2 inches and coarse grout when the minimal dimension is 4 inches.
All grout should be of fluid consistency; the desired slump is 8 inches for units with low absorption, up to 11 inches for units with high absorption.
Whenever possible, grout should be batched, mixed, and delivered in accordance with ASTM C94, requirements for transit mixed concrete.
When a batch mixer is used on the job site, all materials should be mixed thoroughly for at least 5 minutes.
Grout which has not been placed 1½ hours after water is first added should be discarded.
CONSTRUCTION
Prior to laying the first course of masonry units, the general sequence of operations should be determined.
Work should not commence until the layout, dimensions, location of all wall openings, and positioning of reinforcement has been verified.
Foundation alignment must be accurate so that the centerline of the wall stays as close as possible to the centerline of the foundation. Where reinforced hollow block masonry construction is used, dowels of the specified size and length should be