Friday, July 30, 2021

Block Work - Standard Operating Procedure

BLOCKWORK


Introduction:

This standard operating procedure enumerates the scope of AAC Block masonry work to be executed in the Tower area as specified in the approved drawings and at places when instructed by the Tower-in-charge.


Responsibility:  

The respective Tower-in-charge is responsible to execute the work as per the procedure.

Safety & protection:

Blocks shall be stacked properly near the place of work (Do not stack too large quantity  near the work area thereby causing safety hazards)

The height of the stack should not be more than one and a half meters.

Scaffolding to be braced adequately
Working space to be clear of rubbish waste mortar etc so that easy access is ensured.

Scaffolding to be checked for the load-carrying capacity and ensure no overloading.

Material hoists should be checked for load carrying capacity and ensure no overloading. Material hoist third-party safety inspection reports should be submitted by the contractor before using the hoist for material shifting.

Lifting, manual transporting of blocks, etc have to be carried out by workers who are properly trained. Otherwise, this may cause serious injuries to workers.

Chasing in the blockwork has to be carried using appropriate cutting tools only. While chasing the worker must wear proper safety appliances like shoes, goggles, helmets, etc.

Throwing debris from height is strictly prohibited.

Before commencement of blockwork in front of the lift shaft safety permit should be taken.

CT props to be fixed in the front lift shaft to tie the safety belt.

Hard barrication to be cut only by gas cutting (If any anchored in concrete along the openings and edge of the building).
PPEs should be used properly.

Educate the workmen through the pep-talk meetings.


Preparatory works:

Ensure the availability of a detailed layout of the Flat showing room dimensions, the thickness of walls at various locations in the Tower, details of openings (with sizes) to be provided in the walls for doors, windows & other openings. Details of cross walls to ensure proper bond in main walls, location details of concealed items such as electrical conduits, telephone conduits, conduits for TV Antenna wires and cables, location details of items such as water supply pipes with details of the inlet, outlet, and crossings of service lines, sanitary pipes with details of the inlet, outlet and crossings of service lines, openings or holes for positioning of water closet p / straps, openings required for air conditioning ducts, pipe sleeves to be left in walls for other service pipes.

Do check for customer changes prior to execution of blockwork. 

 Starting the blockwork:

Scrub & clean the floor area with the proper tools, where blockwork is to be done.  

Mark the wall lines on the floor to get the proper layout of blockwork, check the clear height between the floor top and the beam bottom/slab bottom, where block work is to be done.

Decide on the thickness of leveling course mortar to avoid wastage/cutting of blocks at the top course and to maintain the gap of 10 to 15mm at top of blockwork. The thickness of leveling course mortar should not be more than 25mm.

Mix quantity of mortar, which will be consumed in the next 2 hours only. Mixing shall be done with proper measurements of ingredients in the proportion of 1:6 with pharma, where 1 part is cement and 6 parts is crush sand. The mixing platform/Tray must be clean. (If more quantity is mixed and will not be consumed within the time, cement will start setting leading to weaker masonry). 

Add water to the dry mix of cement crush sand in the required quantity.

Prepare a scheme of scaffolding, draw a sketch and pass on the same to Workers for execution. Ensure safety aspects such as stability, proper joints, etc. Check and ensure availability of scaffolding materials, access ladder or staircases, working platforms, etc. 


Blockwork base course, alignment & jointing:

Fix one block at both ends of the wall in level as per layout.

Blocks should be wet before placing to avoid absorption of water from mortar.

Carry out leveling course of blockwork with a dry bond (i.e. without mortar in the vertical joints, lay the blocks in position) by fixing line thread on end blocks. Use a piece of plywood to have uniform vertical joints.

Lay mortar for full bed width and for a length of 3 blocks at a time. 

Lay one block at a time & gently pressing it in the mortar bed. 

Excess mortar coming out on the edge (while pressing block in position in bed mortar) to be taken by trowel and reused.  
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. 

Check the layout of leveling course blockwork and then fill all vertical joints of blocks with cement mortar.

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.

Curing to the base course should be done for the next 7days. 


Blockwork with Adhesive: 


After completion of the base course, Blockwork should be done with approved block adhesive. 

Block adhesive should be mixed thoroughly with water in the proportion specified by the manufacturer.

Block adhesive should be applied with an adhesive application trowel only to ensure uniform application.

Before starting the block fixing work above the base course, the positions of full and cut (required size) blocks should be finalized to ensure the staggered vertical joints are at least 6 and to minimize the wastage of blocks. This can be done by making elevation sketches/drawings for walls and pass on the same to Workers for execution.

The adhesive should be applied on both faces were block to RCC joint comes and on one face where block to block joints come.
Clean the surface of the block and apply adhesive on it from the end of the wall. Fix the block on adhesive by pressing it within 3 minutes.

For fixing the next block apply the adhesive on two sides (i.e.- the face of the block fixed earlier and at the top of the below block) and fix the block in position with the help of a wooden mallet. 

Each fixed block should be checked for its line, level, and plumb by a mason. 

The thickness of the adhesive is 3 to 4mm if not checked at the time of fixing will result in unleveled blockwork with the cavities in joints.

While fixing the block between two laid blocks, the adhesive should be applied on all three sides of the block.

Repeat the above points for building more courses.

All joints should be sealed from all sides while fixing blocks.

If the corners of blocks are broken then they should be filled and finished to the surface of the wall with cement mortar.

A clear gap of a minimum of 10mm should be left between the topmost layer and the RCC bottom.

This gap should be filled with very lean mortar and 10mm aggregates should be fixed on the surface. 

This is to prevent the cracks afterward in the wall plastering (due to the presence of different materials like block and RCC).

If the gap is bigger than 20mm the mortar with aggregate should be made to fill it.

In the double-wall area, an opening for water drainage and circulation of air should be made in chajja. After doing three layers of blockwork, ghotai to the chajja should be done with a slope towards the opening. Ghotai should be done on all sides of the box up to 300mm in height.


Height of Construction:

No part of the wall during construction shall raise more than one and a half meters above the general construction level.

Curing:

In hot & dry weather the mortar is likely to dry up before it has attained its final set in the blockwork. This leads to the crumbling of mortar and resulting in weak block masonry. This shall be prevented, by keeping the base blockwork layer constantly wet, for at least seven days. Blockwork is done with adhesive doesn't require curing.


Dos & Do not:

Do stack the blocks on a proper platform & clean surface. 

Do stack blocks at just a convenient location for immediate use. 

Do not overrule safety aspects to achieve timely completion.


Important Note: 

New masons should not be deployed directly on work without Training. The quality department will train the masons. On arrival of new masons at the site, information should be provided to the quality department by the respective Tower-in-charge.

Use Adhesive before its expiry date.


Team
CBEC India