Masonry Magazine February 1996 Page. 44
Fig. 2a. Face shell bedding is typically used in concrete block construction.
Fig. 2b. Full mortar bedding is used in concrete brick and clay brick construction.
Retemper colored mortar cautiously to avoid color changes. Water content and stiffness of mortar during tooling affects color (see section on tooling mortar joints). Filling mortar joints. Two types of mortar bedding are used in masonry construction: face-shell mortar bedding and full mortar bedding (Fig. 2). Face shell bedding is generally used in concrete block or hollow clay masonry construction. Full mortar bedding is used for laying the first or starting course of block on a footing or foundation wall as well as for laying solid concrete brick, clay brick, or solid concrete block. It is also commonly used to construct concrete masonry columns, piers, and pilasters that will carry heavy loads. Where some vertical cores are to be grouted, such as in reinforced masonry, the webs around each grouted core are fully mortared.
Hollow concrete block should be laid with the thicker part of the face shell up. This provides a larger mortar-bedding area and makes the block easier to handle. Mortar is applied to the face-shell bedding surface of the previous course of units. For head joints, mortar is applied only to the face-shell ends of the block. Some masons butter (mortar) the vertical ends of the block previously placed; others set the block on one end and butter the other end before laying the block. Different techniques are acceptable provided the mason makes certain that face-shell head and bed joint surfaces are fully mortared. Buttering both the block already laid and the block to be laid provides well-filled head joints and improved bond (Fig. 3).
Fig. 3. A well-filled head joint results from mortaring both block.
Regardless of the method used to apply mortar to the vertical edges, each unit is brought over its intended final position and pushed downward into the mortar bed and sideways against the previously laid unit. Once laid and positioned, the unit should not be disturbed. Movement will break the bond between mortar and unit. That bond is never fully re-established unless the unit is removed and re-laid in fresh mortar.
For concrete brick as well as clay brick, mortar should be spread to a uniform thickness covering the full width of the bedding surface of the preceding course of masonry. The mortar bed should be furrowed only slightly, if at all. Many project specifications prohibit furrowing of bed joints.
Special care should be taken in filling the head joints. If head joints are not completely filled with mortar, resulting voids and channels may permit excessive moisture to penetrate that wythe of masonry. Mortar should be trow-
Fig. 4. Mortar extrudes from the joints of a unit being placed, indicating full mortar joints.
44 MASONRY-JANUARY/FEBRUARY, 1996