Block work is most important work for the construction of any building. Concrete blocks are very common building components that are used worldwide. There is a wide variety of size and type used within the construction industry today. Let us look at some examples of units used in block work.
Blocks are produced in a range of shapes and sizes. The face side is usually 450 x 225, the thickness varies from 60 mm up to 150 mm and the weight from 6.3 to 15 kg. They are produced in solid, hollow and multi-cut format. Multicuts enable a bolster cut to be made without wastage. Walling built with pre-cast blocks may be divided into two main categories i.e. Load bearing and non- load bearing.
Types of Blocks
Load bearing blocks are pre-cast in moulds and compacted with the aid of vibration, or moulding machines involving the use of compressed air, or a combination of both. These blocks are usually made of concrete comprised of cement and aggregate. The cement is usually Portland cement and a variety of aggregates are used.
Non load bearing block can also be pre-cast in moulds but others are produced in slab format and cut to size when set. These blocks are usually made with a variety of lightweight materials and cement such as Breeze or Clinker waste coke or ash and cement, Burnt clay etc.
Advantages of Concrete Block
Concrete blocks are Versatile, durable and strong, Completely fire resistant, Excellent sound insulation. Also ideal background for dry lining wet finishes and fixings. Inherent thermal mass acts as heat store. These are proven and familiar building method with no risk. Widely and readily available and Cost effective.
Block Work Method of Statement
Materials in this construction activity include:
- Solid and Hollow Concrete Masonry Blocks
- Thermal Blocks
- Damp Proof Course
- Steel masonry accessories, head ties, lateral ties etc.
- Cement based Non shrink grout etc.
Required tools for block work
Below is the equipment involved in the construction of the block works / cavity walls:-
- Nail Gun
- Table Grinder fro block cutting
- Scaffolding Platforms
- Electric drills
- Trowels & Hand tools
- Mixer machine
- Wheel barrow
- Masonry saw
- Mason square
- 3m long Aluminum straight edge
- Spirit level
- Water level
- Measuring tape
- Line dory
- Plumb bob
- Calibrated survey instruments.
The capacity / size of the above equipment shall be judged in accordance with site conditions, requirements, and availability at the time of execution of block work activity.
Safety Requirements for Block Work
Prior to the construction of the block wall, a scaffold spanning the work area is constructed up to the level of the construction. The scaffold is to be designed to be able to hold the material that is to be used in the block wall construction. Scaffolding will be erected so that it will allow each mason free access without being tied off.
All workers working at height will have to wear safety harnesses with lanyard. The area where the block work activities are in progress will be barricaded.
MASONRY BLOCK WORK METHOD OF INSTALLATION
Ensure that bloc work material, sample and method statement and masonry accessories are approved. Masonry delivered to site shall be carefully unloaded & handled to prevent chipping and breakage and random sample to be sent for testing.
Masonry block work units shall be stored in dry location on plank platforms of adequate size. Verify that all reinforcing, anchors, dowels, lintels, flashings, and other built-in items are on hand, of proper size, and locations established. Before commencement of block work ascertain the nature and location of all MEP openings and built in items.
A Mock-up wall of typical wall type shall be constructed and approval to be taken from client. After approval of block work mock-up proceed with masonry works. Concrete block masonry work shall match with approved mock-up wall.
Block Work Procedure
- The surveyor will mark out the layout for the block work using current layout drawings.
- In dry and hot climate, masonry units will be wetted before laying in order to prevent quick drying and shrinkage of cement based mortars.
- 200 thick thermal blocks shall be used for all the external walls or as per approved shop drawings details.
- An approved Damp Proof Course (DPC) material shall be pre-laid into base of the wall along alignment of the block wall. The width of DPC material shall be same as the particular thickness of the blocks specified on the approved shop drawing.
- First layer of blocks to be solid blocks and it should be fully set out with proper alignment.
- Blocks shall be properly laid on a full bed of mortar. Mortar joint thickness for the general purpose mortar will be 8mm to 12mm
- Mortar made on site should preferably be mixed by machine.
Mortar Mixing for Wall Block Work
- Mortar mix ration is 1:6 OPC / Sand for CMU blocks and 1:4 OPC / Sand for thermal blocks or as specified.
- Add and mix thoroughly and uniformly in enough water to make mortar tightly ball in man’s hand and to lightly ooze through fingers as the hand is closed.
- Mix no more mortar at a time than can be used within one and half hour. Mortar not used within the one and half hour time shall be disposed off. Do not re-temper mortar.
- Place masonry to lines and levels indicated. Masonry units shall be set out with a storey rod so that coursing lines up at steel shelf angles, sills, heads of windows and doors with full courses.
- Masonry units will be assembled together overlapped, so the vertical joints are staggered from course to course. At the corners and wall intersections the overlapping should be the minimum width of the units. Only cut dimension units will be used at these locations.
- Horizontal anchors for the masonry block walls will be respected as per specifications.
- All the horizontal joints shall be leveled and vertical joint shall be aligned during construction.
- Cutting of masonry will be done by power driven masonry saw.
General Requirements – Block Works
Walls shall be kept level at all times. Do not install any portion of wall more than 1.2 m in height in any particular day. Carry up walls in a uniform manner, no part being raised more than 1000 mm above any adjacent un-built course, and no area of walling higher than 600 mm, above any course which is not fully set. Angles and reveals shall be kept true, square and plumb. Broken walls must be laid up with a lead.
Walls shall be constructed as true planes and when tested with a 3000 mm straight edge placed anywhere on the wall in any direction shall be true to place within 3 mm and plumb within 4 mm. Each horizontal joint shall be level and at same height in all walls around the room and true to the lines and dimensions indicated on the drawings. Unsatisfactory work shall be removed and replaced.
Intersecting concrete block walls shall be tied together in a masonry bond. Extend masonry partitions, unless shown otherwise, to within 20 mm of underside of structure. Fill the 20 mm gap with insulation under 25% compression, so placed that space is left each side of the finished wall to accept joint sealant
Install reinforced concrete lintels over openings in concrete block walls. Lintels shall a minimum of 200 mm bearing on supporting masonry. Install solid concrete masonry bearing blocks at the jambs of all concrete block. The bearing blocks to be of the same material as the adjacent wall surfaces.
How To Provide Lateral Support
Intersecting bearing walls shall be tied together with a prefabricated “Tee Section” of wall reinforcement or strap anchor set in the second bed course and every third course thereafter, full height of wall. Tops of masonry walls up to 45 mm thick shall be secured to cast-in place concrete slabs above with strap anchors securely fixed to the slab and securely embedded into mortar joints of the wall. Space anchors not more than 600 mm apart.
Block work more than 6 m in height shall be reinforced with reinforced concrete stiffening frame work comprising of 200 x 200 mm verticals at 4.00 meter center and 200 x 300 mm horizontals at mid-height or at every 3.00 meters in case wall height is bigger than 5.00 meters as per the approved shop drawings. When the distance between the structural columns is more than 6.o meters that is the width of panel Block masonry is more than 6.0 meter, and the height and the height of the panel is more than 4.0 m, provide nonstructural columns (200×200) not exceeding 6.0 m on centers as stiffeners.
Stiffener columns and beams shall be provided according to the approved shop drawings and should be approved before any casting of stiffener columns and lintels.
Construct vertical control joints in masonry walls at maximum 6000 mm o.c. Joints shall be constructed full height of the walls or partitions. Joints shall be formed by using one half and full blocks to form a continuous straight vertical joint and placing continuous tarred or waxed paper or asphalt emulsion on the end half-cells of the blocks; the resulting center key cavity is to be completely filled with mortar as each course is placed. Vertical joint between the block ends shall be raked out to a depth of 12 mm full height, both sides and left ready to receive caulking as specified.
MEP Cut out in Block Wall
Maintain openings as per the drawing and cut units to accommodate frames, conduit, fixtures, recesses and other MEP work inside the wall block work.
Doors in Block Wall
As Work progresses, install metal door frames, fabricated metal frames, window frames anchor bolts, plates, conduits, pipes, and other built-in items into Work. All frame work shall be anchored both jams and set plumb and true. Block work shall built to the respective dimension, thickness and height mentioned on the drawing.
Curing the block work
Damp cure the block works for 3 days, lintels and sills for 7 days as per the project specifications.
Cleaning of block work
As the work proceeds, carefully remove mortar splashes from masonry surfaces and adjoining surfaces. After completing each section of the wall block work, clean down surfaces and make good where required.