1. (AAC BLOCK TECHNICAL DATA COMPILATION) DELF INDIA’S TECHNICAL NOTE - 1/2014
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Technical data compilation for Autoclaved Aerated Concrete (AAC) Block masonry
Conforming to IS:2185 (Part 3)–1984, IS:6041-1985 & IS 6441-1972
(i) Manufacturing:
 In block manufacturing, replacement of cement by fly ash conforming to IS
3812-1981 may be permitted up to a limit of 20 percent.(as per clause 5.1.1. of
IS 2185 part 3) However, it shall be ensured that blending of fly ash with
cement is as intimate as possible, to achieve maximum uniformity.
 Suitable steam-curing is necessary in making cellular concrete blocks with
cement as binder’ and the same is absolutely essential when lime is used.
Generally, auto cleaving is done for about 14 to 18 hours at about 788 kPa
and about 185”C, the heating and raising of pressure or cooling and lowering
of pressure being generally gradual over a period of few hours.
(ii) Dimension checks:
The variation in the length of the units shall not be more than 5 mm and variation
in height and width of units, not more than 3 mm. – IS 2185(3) Clause no. 3.2.3
All units shall be sound and free of cracks or other defects
(iii) Specific requirements:
 AAC Blocks shall have block density in range of 650 - 750 kg/cum and
compressive strength in range of 4 - 5 Mpa. - IS 2185 (Part 3) – 1984 Table 1
 The water absorption – as per IS 2185 & test requirement of IS 6441
 Drying Shrinkage - shall not be more than 0.05 % as per IS 2185 (Part 3) – 1984
Clause 8.6
 Moisture movement – as per IS 2185 & test requirement of IS 6441
 Thermal conductivity – 0.24 to 0.30 IS 2185 (Part 3) – 1984 Table 1-Clause 8.6

2. (AAC BLOCK TECHNICAL DATA COMPILATION) DELF INDIA’S TECHNICAL NOTE - 1/2014
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(iv) Storage & preparation of work:
 The block shall be stored in such a way on level ground to avoid any contact
with moisture at site & shall be protected from rain.
 The blocks need not be wetted before or during the laying in the walls; in
case the climate condition so required, the top and the sides of the blocks
may be slightly moistened so as to prevent absorption of water from the
mortar and to ensure the development of required bond with the mortar.
(v) Limitation of use, Wall thickness & Nominal Bond beam: (as per IS 6041 Part 3)
 These Blocks shall not be used in foundation and for masonry below damp-
proof course (Ref – IS 6041 part 3)
 The height of the parapet walls made up of AAC block shall be limited to five
times of its thickness.
 The minimum thickness of non-load bearing internal wall shall be 10cm. The
minimum thickness of external non-load bearing walls in framed construction
shall be not less than 20cm. However, depending upon the local condition
and desired effect of thermal transmission and sound reduction, 15 cm thick
panel walls may be used, provided they are suitably braced and reinforced
by lateral and vertical support.
 These block wall without openings shall have the nominal bond beams (with
min reinforcement) spaced 1200 mm apart & they may be of any length up
to maximum of 18 m (as stated in clause 4.6 – avoidance of crack formation)
 Joint reinforcement shall be as recommended in Table 1 for L to H ratio

3. (AAC BLOCK TECHNICAL DATA COMPILATION) DELF INDIA’S TECHNICAL NOTE - 1/2014
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(vi) Use of Mortar & Application:
 Use of strong mortar with light weight AAC blocks in not recommended. Lean
mortars distribute and accommodate more readily the strains arising from
thermal, moisture and chemical changes. According to IS 6041:1985 blocks
shall be embedded with a mortar, the strength of which is relatively lower
than that of mix used in making of blocks
 Hence Cement send mortar – 1:6 shall be used. - IS 6041-1985 Clause no 3.9.2
Mortar shall not be spread so much ahead of the actual laying of the units
that it tends to stiffen and loose its plasticity, thereby resulting in poor bond.
For most of the work the joints, both horizontal and vertical, shall be 10 mm
thick.
 The laying of block may be started either at the corners first or it may be
started from one end and proceed to the other direction
 Mortar joint shall be struck off flush with wall surface and when the mortar
starts stiffening, it shall be compressed tightly to have a key for plastering
 Chicken mesh shall be used at instants as used in brick masonry works
 Guide lines for chases is masonry walls as per Indian Standard BIS:1905 need
to be followed. The cutting of chases, recesses etc. should be done without
damage to the surrounding masonry. It is desirable to use such tools for
cutting which depend upon rotary motion not on heavy impact for cutting
action
(vii) Sampling for Testing:
 A sample of 24 blocks selected randomly shall be taken from every
lot/consignment of 10000 blocks - from the same grade, size and same batch
of manufacture. (clause 10.1 of IS 2185 part 3)
 All the 24 blocks shall be checked for dimensions and inspected for visual
defects. Out of the 24 blocks, 12 blocks to the test for compressive strength, 3
blocks shall be subjected to the test for block density, 3 blocks to the test for
thermal conductivity, and 3 blocks to the test for drying shrinkage and later to
the test for moisture movement. The remaining 3 blocks shall be reserved for
retest for drying shrinkage and moisture movement, if a need arises. - IS 2185
(Part 3) – 1984 Clause 10.5.2
All tests shall be performed as described in IS 6441 & IS 3349