Copyright Goodheart-Willcox Co., Inc. 118 Section 3 Specifications and Materials • Type K has very low strength and should only be used for interior applications when strength is not a concern. Stone work usually requires a special type of mortar consisting of white Portland cement, hydrated lime, and sand. This mortar prevents stains caused by ordi- nary cements. Mortar in the joints is normally raked back from the surface as the stone is set. Later, the joint is pointed, using the same mortar or a colored sealant. Trade associations recommend proportions of cement, hydrated lime, and sand for mortar. Local building codes also set allowable limits. A typical mixture would be 1 part Portland cement by volume, one-fourth part hydrated lime, and 3 parts sand. Water is added as needed to make the mortar workable. Many brick masons use a special masonry cement containing plasticizing agents to make the mortar more workable. Masonry Accessories Besides the masonry units and mortar, additional components are needed in masonry construction. Bond beams, joints, lintels, and flashing are needed to complete a wall. Bond Beams Concrete masonry walls are usually reinforced horizon- tally and vertically by constructing a reinforced beam or column within the wall. This is done by pouring grout (a flowable mixture of sand and cement) around rein- forcing steel inserted in the units. Special channel blocks are used to form horizontal bond beams, using reinforcing steel and mortar or grout. Vertical bond beams are formed by inserting reinforcing bars in a vertical cell after the wall is laid, then filling the cell with grout. Bond beams are typically used over masonry wall openings such as windows and doors, the top of walls, or anywhere that additional strength is required in the wall construction. See Figure 7-16 for a typical detail showing a bond beam at the top of a wall. Lintels Lintels are members placed in masonry walls above door and window openings. Lintels are supported on either side of the opening. They can be made of precast concrete, steel, or other materials. The door and window schedule will often include the size and type of lintel used. Masonry Joint Reinforcement Masonry walls are reinforced by placing various anchors, ties, and rods in the mortar joints. These reinforcing units are produced in many sizes and shapes for different applications. Reinforcing devices are called out directly on the prints or in applicable building codes. location. Unlike ashlar masonry, which is laid largely at the design of the mason, cut stones are laid according to the design of the architect. Structural Clay Tile Structural clay tile is made of materials similar to those used in brick, but it is a larger building unit. It has many uses in construction—as load-bearing walls, backup for curtain walls, and fireproofing around structural steel. Rectangular open cells pass through each unit, and tile comes in a variety of shapes and sizes. Clay tile has largely been replaced with hollow brick and concrete masonry units. Most masonry walls today are composite walls of a finish surface material and a less expensive backup material. Terra cotta is a type of structural clay tile principally used for nonbearing ornamental and decorative effects. Gypsum Blocks Gypsum masonry blocks are used primarily for interior nonbearing walls, fire-resistant partitions, and enclo- sures around structural steel. Made from gypsum and a binder of vegetable fiber or wood chips, gypsum blocks can be given a plaster finish coat. Gypsum blocks have a face size of 12″ × 30″ and come in thicknesses of 2″, ″ 3″, 4″, ″ and 6″. ″ Mortar Mortar is the binding agent used to hold masonry units together. Mortar also compensates for the differences in brick and stone sizes. Metal ties and reinforcement are secured in mortar. Mortar consists of cement, hydrated lime, sand, and water. ASTM International has established standards for mortar. There are five different standardized types: • Type M has high compressive strength and good durability. It is used for unreinforced underground masonry. • Type S is also a high-strength mortar. Although its compressive strength is not as high as that associated with Type M, it has a stronger bond and greater lateral strength. It also has the greatest tensile strength of any mortar type. Type S is used for reinforced masonry, unreinforced masonry subjected to bending, and in situations where mortar is the only connection between face brick and backing brick. • Type N is a medium-strength, general-use mortar. It is best used for exposed, above-ground masonry. • Type O is low-strength mortar used for interior, nonbearing masonry. This type of mortar should not be used in applications that will be exposed to freezing temperatures.