AAC Block Masonry
We usually observe the cracks in the AAC block masonry wall and try to find out the reasons behind it. This may be a hurdle for us at the site when others point out it by saying bad quality.
But the situation can be reversed if engineers have sound knowledge behind the reasons of these cracks.
Following points can help to avoid the crack formation while using dos and don’ts theory at work.
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| AAC Block Masonry |
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| Crack in AAC Block Masonry |
Checks at DELIVERY
1. Unloading of blocks
1. It is important that the engineers
should monitor the unloading work at site.
2. Blocks should be properly stacked at
site as shown in picture.
3. Stacking in an irregular manner may lead to the crack formation in AAC blocks.
4. Labor should be guided to stack the blocks
slowly-slowly without any fall. Damage blocks should be reported to concern person or authority to take necessary actions against the quality of blocks and
to be returned.
5. Engineers should make sure all the edges of the blocks should
be straight and without damage.
2. Dry Shrinkage
1. Engineers should check the dry
shrinkage limit of the AAC blocks as improper dryness will develop the cracks
in the blocks later on.
2. The reading of the Drying Shrinkage can be checked in the MTC
(material testing certificate) which the supplier shares at the time of
delivery and compare with the fig. given by consultant.
Checks at Execution
1. Number of layers in 1 day
1. It is recommended that the masons
should execute only 6 layers of block masonry in a day.
2. It is because as
per the code we have to place the reinforcement in cement mortar or RCC band
after every 900 to 1200 mm height which depends upon the L/R ratio of wall. Placing of band will be helpful in the formation of cracks.
2. Embedding wires/steel bars
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| Mild steel bars |
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| MS flat strips |
1. It is recommended by code and experts that
after every 900 to 1200 mm layer in height, engineer must embed minimum 3mm diameter mild
steel or galvanized steel or welded wire fabric strip in bed joints or RCC band as discussed above in cement
mortar 1:2.
2. Sometimes, 6mm mild steel is also used instead of above
specification.
3. This will avoid the formation of cracks due to deformation of
floor/roof under the deflection of load.
3. Layer of resilient material
1. The AAC block wall shall be
separated from the ceiling by a gap or by a layer of resilient material or lean
mortar to avoid the crack due to deflection of ceiling under loads.
2. While in
the case of plastered finishes, the risk of cracking can be avoided by forming
a cut between the ceiling plaster and the wall plaster.
3. In order to avoid cracks on walls
due to such movements under load a slip joint to be provided preferably pack
with a resilient material or lean mortar.
4. Bond beam
1. In order to avoid cracks at the
corner of door and window
frames at lintel level or sill level, it is desirable
to provide a nominal reinforced concrete bond beam at sill level and a vertical
reinforced concrete stud at either side of the vertical members of frames.
2. Apart from that, it is recommended
that bond beam should also be provided in the AAC block masonry wall to avoid
cracks.
3. Their location can be at floor level, at top of all door and window
openings, below the sill, and at the plinth level subjected to the
recommendation from the structural consultants or as per the code.
5. No to chisel & hammer
1. Engineer should not be allowed
chisel and hammer for chasing out work in block wall for laying conduit, plumbing pipe purposes as it will disturb the joints of wall.
2. These actions will lead to the formation
of cracks. Therefore, cutter machines should only be used.
3. Apart from that mason should not
allowed to use chisel & hammer for cutting of AAC blocks as it will also disturb
the inner structure of the block.
4. For the cutting of blocks, handsaw or hexa
should be used.
6. Thickness of mortar
1. The mortar thickness in any case
should not be more than 3mm.
2. Engineers usually get confuse to choose between
cement mortar and adhesive.
3. Here, it is recommended that AAC block should be
fixed with adhesive as it will give the flexibility during the expansion and
contraction of block which is not in the case of cement mortar because it binds
the block tightly and does not allow it for expansion and contraction, which
leads to the formation of cracks later on.
Checks - During Plaster Work
1. The use of Gypsum Plaster will aid
to avoid the crack formation in the AAC block wall because the density of Gypsum Plaster and AAC block is almost same due to which there is not so much
difference between their thermal expansion and contraction.
2. Use of wire mesh on joints can
also be used to prevent from the cracks.
Conclusion:
- It is recommended that the engineers must pay attention to all above points and closely monitor the masonry work by filling the checklist sheet.
- Engineers must look the skill set of the masons. The manpower must know about the procedure of laying and handling the blocks.
- It will be recommended that engineers must call the technical or trainer executive from AAC block supplier to trained the masons for work.
- Shifting and handling of AAC blocks should be taken care otherwise wastage will be increased.
- Engineers must send the blocks for the testing in a lab. It
is advisable to go through the Codes and instruction given consultants at once to avoid the cracks on
wall.
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