Scope: This is to provide a method statement for construction of Block work in accordance with standard specifications and relevant drawings.
Procedure : This work should be done in accordance with the standard specification and frequency of test to be conducted as per Quality Assurance Plan (QAP)
Checks before Starting block work:
- Make sure that the area, where block work is to be constructed is as per the architectural drawings, and drawing dimensions are matching with the field conditions
- Ensure that blocks obtained from approved vendor, which meets the minimum requirements of 4N/mm2 of compressive strength for hollow blocks and 7 N/mm2 for Solid blocks
- Make sure for all other materials like Cement and M sand also meets the require parameters and should submit Manufacturing test certificate (MTC) before unloading at the project site
- The term Hacking is used at various instances during construction.
- It is synonymous with various activities such as. Striking a surface with a special tool so as to roughen it to take plaster.
- Hackings to be done in advance, for all contact surfaces of beams, columns, staircases and roof slabs, where block work is to be constructed.
- Generally 80 No’s of hackings are required per Sft of area or at least 50 – 60 no. is must.
- The length of hacking is 25 mm, width and depth should not less than 3 mm if manual hacking is adopted (Fig 2).
- If we can go for machine hacking using Grinding machines ( Fig 1 ) then it should be 50 mm x 4 mm x 4 mm.
- The best pattern of hacking is forward strokes followed by reverse strokes.
- Apply a coat of cement slurry in the ratio 1:2 for the hacked surface and curing to be done for 3 days before starting block masonry. This will enhance the better bonding between the concrete surface and regular mortar going to be used during block work.
Preparation of Work, and shifting of Materials and Components:
- When all the materials and components are distributed or shifted to the work area at higher floors, make sure that the place of unloading over structural slab is not overloaded.
- To maintain this, stack the blocks in lines, one above the other and limit the height of stacking to 1 meter. (Fig 3)
- Make a good Plan for staging material required for block masonry at heights.
- Plan for extra manpower for shifting and lifting blocks by properly using wheel barrows to higher levels. (Fig 4)
- Mark the exact position of doors, windows and ventilators openings in block work to avoid unnecessary cutting blocks, and shoddy adjustment of masonry unit’s results in insufficient bonding.
- Always transfer a level of 1 meter height from finished floor level, for columns and walls in all rooms and floors, so that all sills, lintels, chajjas, door frames and window frames can be fixed with respect to this level.
Preparation of Mortar Mix:
- Always go for professional way of Mortar mixing by using Mixer, except for small quantities only Hand mixing can be done on a Metal tray which acts as a watertight platform. ( Fig 5)
- When mixed at site, use measuring boxes for correct and consistent mixing ratio of cement mortar.
- Always mix mortar in 1:5 ratio and in manageable small quantities so that it can be consumed within max. 2 hours (1-2 hours) of its mixing.
Tools required for Block work:
Masons Trowels (small and medium), Line thread, Sand Sieve, Spades, Pans, Measuring boxes, Metal tray, Tube levels, Plumb bobs, Measuring Tape, Spirit levels 1-2 m, Aluminium straight edge, Right angle, Chipping Tools, Masons hammer, Leveling threads, Masons brushes and buckets, Water Barrel and Wheel barrows.
Checks required during block work:
- Base course : Keep the base course or first course of block, after checking the plumb thoroughly with respect to the beam and alignment with respect to the columns. Cross check with PMC and Quality consultant.
- Mortar joints : Maintain minimum thickness of Mortar joints and should not be more than 10 mm for both vertical and horizontal joints. The joints should be neatly raked or pointed using an Aluminium Straight edge.
- Height of block work is restricted to 1 meter height per day.
- RCC band : For 4” block work or partition wall masonry, Provide RCC band of 100 mm thick in 1:2:4 mix or M 200 grade with reinforcement of 2 No’s of 8 mm dia. steel at every 1 meter height of wall construction. ( Fig 6)
- Always follow the principle that, block work for the present floor is constructed one course below, beam bottom and can be constructed the same after the next floor block work is raised in the same fashion, one course below beam bottom.
- Screed concrete : In the terrace floor, first build the parapet wall and do the waterproofing and screed concrete before placing and packing the last course of masonry in the previous floor.
- Always avoid using thin blocks or concrete band, say about 2- 3” thick for top most course, rather go for the same, two courses below the beam bottom.
- Dowel blocks : For continuation of block work use dowel blocks, so that staggered joints or interlocking joints can be utilized in best manner.
- Electrical Groove cutting : For Electrical conduits chasing in block work, use appropriate chasing machines and avoid manual chasing as well as horizontal chasing. Go for chasing after at least 21 days of block work completion and for tiled surface walls, it is better to chase after first coat or rough plastering work completed and well cured.
- For Electrical pipes packing in block work, joints having more than 10 mm width, and more number of pipes accumulated in restricted place for junction box, DB, MCB etc. should be done in PCC 1:2:4 using 12 mm jelly and curing to be done for at least 3 days.
- Block work date to be mention over wall surface in paint and accordingly monitor curing works for 7 days.
- Provide bearing of 200 mm for all sill, lintel and chajjas with bed block.
Care to be taken after block work:
- Do not go for excessive conduits chasing, which distracts the masonry joints results in developing cracks and weakening the work.
- The Junction between block and all concrete structures like columns, beams, staircase and roof ceiling are most critical zones and needs special attention. This is due to inconsistency of bondage between two different materials. Before starting plastering, these zones should be properly treated. (This will be dealt separately under plastering)
- After completion of 7 days curing period, it is time for testing of mortar joints by striking a nail into the joint. This is required to test the strength of joints at random.
- Check the work is executed as per the approved drawings at site.
- Block work should fulfills the requirements of alignment, verticality without bends and uniform level as the basic principles of civil engineering.
- Ensure all the dimensions including the diagonals are equal, with metallic measuring tape.
- Check all openings for doors, windows, lifts, cut-outs etc. including its diagonals for accuracy.
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