Carry out one row of block work with ‘‘dry bond’’ (i.e. with out mortar, lay the blocks in position), the wall to establish the proper spacing of blocks. Lay mortar for full bed width and for a length of 3 blocks at a time, and to 12mm thickness. Lay one block at a time & gently pressing it in the mortar bed. Use a line thread from one end to end with a line pin.
All block work shall be plumb, square and properly bonded. The block joints shall not be broken. Excess mortar coming out on the edge (while pressing block in position in bed mortar) to be taken by trowel & buttered to the cross directional joint or head joint surface of the next block being laid.
The thickness of courses shall be uniform with courses horizontal. Use straight edge & spirit levels on top of the blocks laid & check the top level. Make sure that the spirit level is in working condition & read the bubble carefully. Lay the last closure block in the course, to close the bond and locate it to be near the center of the wall normally. Butter both edges of closure block with mortar before laying.
Repeat the above points for building more courses. After every two course of block work laid, check the verticality using plumb bob, sight down the wall. The whole block work to be built in uniform layers. For pointed masonry without plaster, smooth textured concrete block shall be used. The face of blocks work shall be kept clean at all times. Where block are to be used for load bearing walls, the uppermost layer of block masonry supporting slab or other structured members, shall be solid or treated as directed.
Striking of joints:
As soon as mortars in the joints have initially set, use a proper tool and strike the vertical joints first. The horizontal bed joints are to be raked next to a depth of 10 mm. After “striking joints” brush the wall surface head joint first & bed joints last to complete brushing. If, it is exposed block work with out any plastering, the striking of joints should be 15mm in depth instead of 10mm.
Height of Construction: No part of wall during construction shall raise more than one and a half meter above the general construction level.
In hot & dry weather the mortar is likely to dry up before it has attained its final set in the block work. This leads to crumbling of mortar and resulting in weak block masonry. This shall be prevented, by keeping the new block work constantly wet, for at least seven days.
General Requirements in block work:
In load bearing structures the top layer of block work has to be plastered smooth. (This is to prevent the slab concrete getting attached to the block work thereby causing cracks just one block after the top most layers).The junction of block work with the RCC beam or ceiling must be filled with dry sand or very lean mortar. This is to prevent the cracks afterwards in the wall plastering (due to presence of different materials like block and RCC). To receive lintel or beam in position in the block work, the bearing must be plastered on such blocks without fail.
Do’s & Don’ts in block work
- Do stack the blocks on a proper platform & clean surface.
- Do stack blocks at just convenient location for immediate use.
- Do not over rule safety aspects to achieve timely completion.