Burnt clay brick walls
• This example, developed at the CBRI, Roorkee, India, shows how simple devices and a well organized work place can not only increase the speed of construction (field trials resulted in a 30 percent increase), but also greatly improve the accuracy and quality of brickwork. All that is needed is a set of end-frames for different wall thicknesses and heights, string holders that can be used with any straight, vertical member, of rectangular cross-section (eg concrete columns), boards to hold the mortar, a few accessories, and a well worked out plan of action.
• The mortar used for laying the bricks and for plastering must satisfy a number of requirements: it must be easy to spread, remain plastic as long as it is being applied, but then harden rapidly to resist deformation.
• Mortars basically consist of sand and a suitable binder, in most cases ordinary portland cement, in proportions varying from 1: 3 to 1: 12 (cement: sand), depending on the strengths required. However, the use of OPC alone makes a harsh mortar, which achieves undesirably high strengths. Hence it is advisable to add lime, which makes a more workable mortar, prevents cracking and achieves strengths that correspond to those of the bricks.
• The high costs of OPC can be reduced by replacing 30 % of it by a suitable pozzolana (see section on Pozzolanas). Further information: Bibl. 22.03.
Bricklaying With Higher Efficiency
• With a few end-frames (as illustrated) the usual, time- consuming process of plumbing and stringing the wall is avoided. Each end-frame consists of two wooden planks held at right angles by a welded steel frame. The widths of the boards correspond to the wall thickness, ie half, one, or one and a half brick length.
• Simple L-shaped wooden string holders, which are held in place by the tension of the string, are slid along the edge of the frame as required. Accurate marks on the frame, corresponding to the height of the brick plus mortar joint, eliminate the need for measurements at each layer.
• Higher efficiency is also achieved by improving the layout of the work place. The principal idea is to place stacks of bricks and mortar boards in alternate succession parallel to the wall under construction, at a distance of 50 - 60 cm for the mason to move along. The bricks are placed on edge for the bricklayer to grip easily. The mortar is placed on the boards, substituting the traditional metal pans, which the masons normally hold in one hand. Bricks and mortar are continuously supplied from the other side by helpers.
• The mortar is picked up on a trowel and unloaded on the wall while moving along it for a distance of about 1 m. Then 8 - 10 bricks are placed in line with the string, each time filling the vertical joints with mortar. The procedure is then repeated for the next metre and so on. For each new layer the string holders are just pushed up to the next mark.
• The string holders can also be used independently for filler brick walls in framed buildings by fixing them directly on the reinforced columns. The method is equally applicable for work on scaffolding.
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