Detailed work procedure for AAC Blockwork activity

[Srinivasan]

Detailed work procedure for AAC Blockwork activity

Before Starting Blockwork

1. Follow the latest “Good for Construction” drawings duly signed by the architect.
2. Check for any variations/deviations from the approved architectural and services drawings.
3. All concrete surfaces of beams and columns coming in contact with block work is to be hacked (80 indents per sq.ft. and each indent is considered to be 1 cm long)
4. Use cement mortar slurry of 1:2 on the hacked surface to create a roughened surface for proper bonding, 3 days prior to start of block work. Cure the roughened surface for these 3 days, by spraying water.
5. Aluminium templates provided by SGMPL should be available at site to ensure correct door / window openings.
6. For non-load bearing walls use solid / hollow 4 N/mm2 compressive strength blocks or as specified by structural consultant. For load bearing walls use solid / hollow 7 N/mm2 compressive strength blocks or as specified by structural consultant.
7. Use silt free (less than 5%) medium gritty clean sand for mortar.
8. Approved grade cement not more than 30 days should be used. The date of manufacture is put on the bag.
9. Ensure that all required tools, accessories and materials are available at the place of work.
10. Finished floor level should be button marked on structural slab. Lintels, chajjas and sills to be cast with respect to finished floor level.
11. For bonding of block work to columns, wall ties shall be cast into columns at a vertical spacing not greater than 500mm and should be aligned with the horizontal mortar band.

Procedure during Blockwork

1. Place the marker course of block (1st course) after checking the vertical & horizontal alignment. Get it checked by the architect.
2. If hollow blocks are used fill the lowest (1st course) with concrete 1:3:6 using 12mm jelly to give a firm base for chipping to fix skirting.
3. Mix mortar in proportion of 1:5 on MS sheet, using Farma box for measuring sand and a measuring can to standardize quantum of water to get a consistent mix. Mix well for uniformity. Mix mortar in small manageable quantities and use it within ½ an hour.
4. Mortar joints should not be more than 10 mm for both vertical and horizontal joints. The joints should be neatly pointed using an Aluminium Straight edge or German pointing trowel.
5. Do not construct more than 1 metre height in a day.
6. Give concrete band of 1:2:4 with 8 mm steel (2 Nos.) in a 100 mm thick wall at every 1 metre height.
7. Do not place the topmost block under the beam until the immediate upper floor blockwork is raised up to the beam bottom, less one course.
8. In the top floor, build the parapet wall and do the waterproofing and screed concrete before placing and packing the last course.
9. Adjuster course in concrete 1:2:4 should be laid two in courses below the beam and not above the topmost course.
10. Use hollow blocks at the location of electrical conduit and raise the conduit along with the blockwork.
11. Dowel blocks to be left for further extension of block masonry.
12. Continuous horizontal chasing should be avoided. Chase blockwork using chasing machines.
13. Start chasing after at least 21 days of blockwork construction
14. For tiled surfaces it is a better option to chase after rough plaster is done and cured for 21 days.
15. All nibs adjacent to columns and less than 200mm, should be cast in RCC at site using M20 grade of concrete and curing for 7 days by covering with hessain clothes.
16. For mortar joints more than 10mm, packing of chasing for pipes, junction box etc. should be done in P.C.C. 1:2:4 using 12mm jelly and cured for minimum 3 days.
17. Write down the date of work in paint on the blockwork and monitor the curing accordingly.
18. Cure the blockwork by spraying water on the mortar joints only for at least 7 days.
19. Cast the cut lintel, sill, and chajja by giving a maximum bearing of 200mm and with bed block.
20. In the case of lintel, sill, and chajja over large openings, place them as end-to-end beam type.
21. If bearing cannot be given as required, lockset the reinforcement of lintel into the column for a depth of 4d for cast in situ works.
22. Check chajjas and sills for toppling effect. If suspect, build counterweight courses for lintel, sill, and chajjas.
23. Continuous vertical mortar joints should be staggered and vertical movement joints to be given every 12 metres.

Care to be taken after Blockwork

1. Do not entertain excessive chasing as it disturbs the mortar joints causing hairline cracks and weakening the work.
2. Do not soak the blocks with water while curing. The moisture absorbed by the blocks will be released subsequently causing volumetric variations and shrinkage cracks.
3. The interface between block and concrete is the most critical zone and needs special care. This is due to incompatibility between two heterogeneous materials. Before plastering, these zones should be given special treatment. (Discussed separately under plastering)
4. After 7 days curing of mortar joints drive a nail into the joint to test the strength of joints at random. Also look for colour variation in the mortar joints to identify problem areas.

Required tools must be available at site to ensure correct work. Basic tools of the masons are:
Trowels
Line dori
Sand Sieve
Tube levels
Plumb bobs
Measurement Tape
Spirit levels 1-2m
Aluminium straight edge
Right angle
Chipping Tools
Masons trowels
Masons hammer
Levelling threads
Masons brushes and buckets
Mortar boxes
Water Barrel



Inspection Methodology for Quality Assurance

1. First measure if the given area is to plan as per correct and updated drawings
2. The blockwork should be neat and clean visually
3. The first course in block-work is the most important one. Using the spirit levels, check if the erected wall is perfect – the surface should be free of undulations, and cracks.
4. Using the tape measure, ensure the diagonals are equal.
5. Check if the mesh used at required joints are properly placed & plastered.
6. Using the 3-meter Spirit levels and aluminium flats check if the erected surface is parallel. Check plumb at door and window openings
7. Measure openings at various points for uniformity. If in doubt, crosscheck with diagonals.
8. Check if the corners are at right angles using the right angle template.
9. Ensure door and window aluminium templates are always readily available.
10. The joints should be of uniform thickness. Check joint thickness and strength after 7 days (nail test)
11. Always use blocks of the same height and dimensions [Two different sizes have been observed of 190mm and 200-205mm respectively]

Tools to be used for Quality Inspection
Measuring tape
Spirit levels - 3m
Right angle template
Related “Good for Construction” drawings