Masonry Magazine September 1975 Page. 15
Unless otherwise specified, the top of the foundation should be broom cleaned to remove loose mortar and debris. The top of the foundation should be damp when the first course is laid. The first course should be carefully laid in a full mortar bed. Do not furrow the bed; this will permit the grout to come into direct contact with the top of the foundation.
Unless otherwise specified, hollow units are normally laid with mortar coverage on horizontal and vertical face shells. Webs are also covered where they are adjacent to a cell or cavity which is to be grouted so that grout will be confined to that area. If wall is to be fully grouted it is not necessary to cover the cross webs with mortar, since the grout will flow into these spaces.
As masonry units are laid in the wall the mason generally strings the bed joint mortar several units in advance of the units being laid. The inspector should check that this mortar does not stiffen to the point where units being placed on top will not properly bond. The proper distance for stringing bed joints will depend upon temperature and speed of laying.
It is important that bearing walls be kept level and plumb, and in multi-story walls that they line up accurately one on top of the other. Allowable tolerances for concrete masonry construction based on actual dimensions are as follows:
Variation from the Plumb
1. In the lines and surfaces of columns, walls and arrises:
in 10 feet 1/4 inch
in any story or 20 feet maximum 3/8 inch
in 40 feet or more 1/2 inch
2. For external corners, control joints and other conspicuous lines:
in any story or 20 feet maximum 1/4 inch
in 40 feet or more 1/2 inch
Variation from the level or grades indicated on the Drawings
1. For exposed lintels, sills, parapets, horizontal grooves and other conspicuous lines:
in any bay or 20 feet maximum 1/4 inch
in 40 feet or more 1/2 inch
Variation of the linear building lines from established position in plan and related portion of columns, walls and partitions:
In any bay or 20 feet maximum 1/2 inch
in 40 feet or more 3/4 inch
Variation in cross-sectional dimensions of columns and in the thickness of walls:
minus 1/4 inch; plus 1/2 inch
For reinforced masonry construction steel reinforcement must be free of surface materials such as mud, dirt or oil that would impair the bond to mortar or grout. Bends or kinks in bars caused by handling incident to delivery should be straightened out without injury to the material before placing it in the masonry. Reinforcing steel should be located as shown on the drawings and held in position at not over 192 bar diameters on center or frequently enough to prohibit displacement during grouting. Unless otherwise noted on the plans, vertical bars are placed at the centerline of the wall. Vertical bars do not necessarily have to be located in the same core as a foundation dowel. They may be in adjacent cores and grouted to the full height of the dowel. The cores containing vertical wall steel, of course, are grouted to the full height of the bars.
The thickness of grout or mortar between masonry units and reinforcement should be not less than 1/4 inch except that 1/4 inch bars may be laid in 1/2 inch horizontal mortar joints, and No. 6 gage and smaller wires may be laid in 3/8 inch horizontal joints. Horiontal reinforcement in bond beams may rest on cross webs of the units.
Grouting
Grouting of hollow block construction requires that the units be aligned to form an unobstructed, continuous series of vertical spaces within the wall framework. Spaces that will contain reinforcement should have a minimum width of 2 inches. Proper preparation of the grout space before grouting is very important. All mortar droppings and debris should be removed through the cleanout openings. Mortar that protrudes more than about 3/8 inch into the grout space should be removed so that grout will not bridge at these locations causing incomplete filling of cores. Where low-lift grouting is used, this is done during erection and checked prior to grouting. If high-lift grouting is used, protrusions can be knocked off and removed through the clean-out openings.
After the grout spaces are checked for cleanliness and reinforcement positioned, the clean-outs are then closed by inserting face shells of masonry units, mortaring in units that were left out, or by forming over the openings to allow grouting to the plane of the wall. Face shell plugs or mortared units should then be adequately braced to resist the fluid pressure of the grout. In hollow unit masonry, the mortar should be permitted to cure 24 hours before grouting to prevent mortar joints from being blown out by fluid pressure from the grout. When filling the cavity space between two wythes of masonry, a period of not less than 3 days is recommended to prevent "blowouts".
Procedures used in grouting are important. In low-lift grouted construction, grout should be consolidated at time of pouring by puddling or vibrating. In high-lift grouted construction, grouting is done in a continuous pour, in lifts appropriate to avoid blowouts. It should be consolidated by puddling or vibrating during placing, and reconsolidated after excess moisture has been absorbed but before workability is lost. In high-lift grouted construction, the grouting of any section of wall should be completed in one day with no interruptions greater than one hour. If grouting is stopped for longer than one hour, horizontal construction joints should be formed by stopping the pour of the grout at least 1 1/2 inches above or below a mortar bed joint,
Prism Testing
Where prism testing is required, the test prisms should be a representative sample of the actual composition of the wall. Each test prism should be