Setting Stone

Ashlar stone that is laid in straight horizontal courses can be installed using string lines and line blocks just like unit masonry. For rubble stone that is less precise, pattern bonds are more like putting together a puzzle in which no two pieces are the same size or shape. There is an art to cre- ating uniformity in pattern so that the front of the house looks the same as the sides and back. Colors must be blended and some regularity of coursing and placement is required. The necessary skills can be acquired only with hands-on experience and a good eye for the esthetics.

5.5.4

Flashing and Weep Holes

Even though stone is not as absorptive as brick or block, stone masonry walls still require flashing and weeps to drain moisture from the wall. Water entry in stone walls, like in brick and block walls, is most often

through the mortar joints, and when the joints are irregular and diffi- cult to tool, water penetration can be significant.

5.5.5

Accessories

Residential stone masonry usually is limited to veneer applications, garden walls, and retaining walls. Steel reinforcement is seldom nec- essary for these applications, so the accessories necessary for stone masonry construction are usually limited to wall ties and anchors. These need flexibility to accommodate the irregularities of the stone, and either wire or corrugated metal are most frequently used.

5.6

Grouting Masonry

Concrete block basement walls often require steel reinforcing for added strength. In reinforced concrete block construction, the cores of the hollow units are pumped with grout to secure the reinforcing steel and bond it to the masonry. All of the cores of a concrete block wall may be grouted with reinforcement spaced every few cores, or the grout may be limited only to the cores which contain reinforcement.

If only isolated cores of a concrete block wall will be grouted, the cores that will be grouted must be fully bedded in mortar, including the webs and face shell flanges. This will prevent the grout from flow- ing beyond its intended location. If the whole wall is to be grouted, the face shells are mortared as usual, but the webs are not. This allows the grout to flow laterally inside the wall for better bond. Spacers are used to maintain alignment of the vertical reinforcement to assure that grout completely surrounds the steel for full embedment and proper struc- tural performance. Protrusions or fins of mortar which project into the cores will interfere with proper flow and distribution of the grout and could prevent complete bonding.

The low-lift method of grouting a wall is done in 8-in. lifts as the wall is laid up. Grout should be well mixed to avoid segregation of materials, and carefully poured to avoid splashing on the top of the units, since dried grout will prevent proper mortar bond at the suc- ceeding bed joint. At least 15 minutes should elapse between pours to allow the grout to achieve some degree of stiffness before the next layer is added. If grout is poured too quickly, and the mortar joints are fresh, hydrostatic pressure can cause the wall to bulge out of plumb. A

displacement of as little as Ⲑ8in. will destroy the bed joint bond, and the work must be torn down and rebuilt. The joint rupture will cause a permanent plane of weakness and cannot be repaired by simply realigning the wall. Grout that is in contact with the masonry hardens more rapidly than that in the center of the grout space so it is impor- tant that consolidation or puddling of the grout take place immedi- ately after the pour and before this hardening begins. Vibrators used in masonry grouting are usually smaller than those used in concrete work because the space they must fit into is smaller. In single-wythe, hol- low-unit construction, walls may be built to a maximum 4-ft. height before grout is pumped or poured into the cores. Grout is placed in the cores and then consolidated by vibration to ensure complete filling and solid embedment of steel.

High-lift grouting operations are not performed until the wall is laid up to full story height. The cross webs of hollow units are fully embedded in mortar about every 25 ft. to form grout barriers. This lim- its the size of the pour to a manageable area and contains the grout within the designated area. Cleanouts must be provided at the base of the wall by leaving out every other unit in the bottom course of the sec- tion being poured. In single-wythe, hollow-unit walls, cleanout open- ings at least 3⫻4 in. are located at the bottom of every core containing dowels or vertical reinforcement, and in at least every second core that will be grouted, but has no steel. In solidly grouted, unreinforced sin- gle-wythe walls, every other unit in the bottom course should be left out. A high-pressure air blower is used to remove any debris which may have fallen into the cores. Cleanout plugs are filled in after clean- ing the cavity, but before the grouting begins. The mortar joints in a wall should be allowed to cure for at least three days to gain strength before grouting by the high-lift method. In cold, damp weather, or dur- ing periods of heavy rain, curing should be extended to five days. Grout should be placed in a continuous operation with no intermedi- ate horizontal construction joints within a story height. Four-foot max- imum lifts are recommended, with 30 to 60 minutes between pours to allow for settlement, shrinkage, and absorption of excess water by the units. In each lift, the top 12 to 18 in. should be reconsolidated before or during placement of the next lift.

It is critical that the grout consistency be fluid, and that it be mechanically vibrated into place. When the grout is stiff, it hangs up

on the side walls of the cores and the rein- forcing bars, leaving voids in which the steel is not properly bonded or embedded and is much more susceptible to corrosion from moisture within the wall.

5.7

Protections

During construction, partially completed masonry work requires some protection from damage caused by weather or by other construction operations.

5.7.1

Bracing

High-lift grouting requires that walls be temporarily braced until the mortar and grout has fully set. Partially completed walls should also be braced during con- struction against lateral loads from wind or other forces applied before full design strength is attained or before permanent supporting construction is completed (Fig- ure 5-32). Partially completed structures

may be subject to loads which exceed their structural capabilities. Wind pressure, for instance, can create four times as much bending stress in a new, freestanding wall as in the wall of a completed build- ing. Fresh masonry with uncured mortar has no tensile strength to resist such lateral forces. Most codes require that new, uncured, unan- chored walls be braced against wind pressure. Bracing should be pro- vided until the mortar has cured and the wall has been integrally tied to the structural frame of the building. Bracing should be designed on the basis of wall height and expected wind pressures.

5.7.2

Coverings

Masonry walls should be covered at the end of each day and when work is not in progress. Excess moisture entering the wall during con- struction can cause saturation of units, which may take weeks or months to dry out. Such prolonged wetting may result in efflorescence,

TEMPORARY BRACING

F I G U R E 5 - 3 2

Bracing provides wind load resistance during con- struction. (from NCMA, TEK 72, National Concrete

particularly if the cooler winter months lengthen the drying process. Extended wetting will also prolong cement hydration, producing large amounts of calcium hydroxide, which may also be taken into solution and leached to the surface to cause calcium carbonate stains.

Covers such as water-repellent tarps or heavy plastic sheets should extend a minimum of two feet down each side of uncompleted walls and be held securely in place. During construction, scaffold planks should also be turned on edge at the end of each day so that rain will not splash mortar droppings or dirt onto the face of the masonry.