Masonry Magazine October 2000 Page. 20
Masonry Cement and Mortar
Masonry cement is a hydraulic cement, that is, it hardens by chemically reacting with water and will do so under water. It consists of portland or blended cement and inorganic plasticizing materials (such as pulverized limestone, hydrated or hydraulic lime) together with other agents introduced to optimize workability, board life and water retention, contribute to improved durability; and reduce drying shrinkage and water absorption of mortar.
Mortar cement is a relatively new product designed for use in demanding structural masonry applications. Mortar cement, like masonry cement, is a hydraulic cement, primarily used to produce masonry mortar. However, mortar cement must meet lower maximum air content limits than masonry cement and is the only mortar material or system that has minimum bond strength requirements.
Whether present as an integral part of masonry cement or as a separate ingredient added at the mixer with hydrated lime, portland cement acts as the glue, which holds the mortar and, ultimately, the masonry, together. Compressive strength and bond strength are related to the portland cement content of mortar.
Hydrated lime may be batched with portland cement, sand, and water at the job site. In this system, lime functions as a plasticizer contributing to workability, board life, and water retention of the mortar.
Either air-entrained portland cement or air-entrained hydrated lime may be used to improve the workability and durability of the portland cement-hydrated lime mortar. However, air-entrained cement and air-entrained lime should not be combined in the same mix.
SELECTION
Once the design loads, type of structure, and masonry units have been determined, the mortar type can be selected. Table 3, adapted from ASTM C 270, provides guidelines for selecting mortar for unreinforced (plain) masonry. It should be remembered that stronger is not necessarily better when selecting mortar for unit masonry. For example, it is not typically necessary to use Type M mortar for high-strength masonry. Type S will provide comparable strength of masonry, and in fact the Masonry Standards Joint Committee's design standard ACI 530/ASCE 5/TMS 402 does not distinguish between the structural properties of masonry constructed using Type S mortar from that constructed using Type M mortar. Moreover, Type S and Type N generally have better workability, board life, and water retention. As a rule of thumb, the specifier should not require use of a mortar of higher compressive strength than necessary to meet structural design criteria.
Unless otherwise indicated, either a masonry cement or cement-lime mortar may be used. Masonry cement mortars, generally offering improved convenience, workability, durability, and uniformity, are used in a majority of masonry construction. For structural masonry, the designer may require Type S cement-lime mortar or mortar cement mortar if the allowable tensile flexural stress values associated with these mortars have been used in the design of the masonry. Codes may also require the use of Type S cement-lime or mortar
Great Ideas In Masonry Construction
Great Ideas In Masonry Construction one of a series Introducing... Hook Shield* The Mortar Stops Here! When inadvertent mortar droppings occur, they don't get past Hook Shield, the completely different approach to stopping excess mortar! Hook Shield installs easily with any hook-and-eye, triangle or adjustable tab system, on any veneer anchoring system. The Hook Shiekl system accommodates any size cavity and may be used on very high walls.
It's A Snap! Constructed of rigid plastic, each Hook Shield piece snaps into place quickly, supported by the stability of the double hook. Double eyelets, placed alternately on the lower courses of masonry, provide staggered spacing for Hook Shield. Mortar droppings are suspended and will not fall to the bottom of the cavity. This avoids mortar buildup and allows moisture to exit through weeps and vents. Hook Shield is easy to handle, and it's economical. Four small boxes, each containing 100 pieces, require only two cubic feet of storage. Each box contains 225 picces which can provide excess mortar protection for approximately 100 linear feet of masonry wall cavity. Mortar just doesn't get past Hook Shield. It's the new alternative for stopping excess mortar! Call us today at 1-800-MRCA (6722) concerning Hook Shield or any of the items in our complete line of masonry joint reinforcement materials and accessories. We're always searching for new solutions in the masonry industry. "Patent # 5,845,455 1-800-849-MRCA (6722) WIRE-BOND Masonry Reinforcing Corp. of America Innovation In Masonry Construction www.wirebond.com
20 MASONRY-SEPTEMBER/OCTOBER, 2000