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Old 04-08-2013, 11:13 AM   #1
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Cracks in AAC Blocks


Hello All


There have been long long almost 2/3 the length of the wall crack in AAC Block Masonry

The Cracks are horizontal and vertical , almost on 7 out of 10 blocks wall in house .

Its a normal G+1 Structure .

The Blocks are laid in normal Sand and Cement Mortar . 1:5

The Walling was done before 3-4 months

i'll be glad if any one can tell me solution and help me out in finding reason for the cracks .

Thank you

http://postimg.org/gallery/2nnq228q/

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Old 04-08-2013, 03:20 PM   #2
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Cracks in AAC Blocks


AAC blocks are relativley new in the US, but have been used in Europe for years. They're dreadful. All concrete block walls undergo an initial shrinkage, resulting in cracking on long walls. In quality work, movement joints are usually incorporated to control the cracking.
But these AAC blocks are the worst. I've seen them shrink to the extent that they pull ceramic tiles off walls.
Having said that, it's nothing structural; you'll just have to go round caulking up the joints when the shrinkage has finished.

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Old 04-09-2013, 05:02 AM   #3
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Cracks in AAC Blocks


for the rest of us ignorant oafs, aac block is autoclaved aerated concrete - wikipedia.org/wiki/Autoclaved_aerated_concrete - lite weight, pre-cast units w/no coarse aggregate - provides structure, insulation, fire, & mold resistance

sounds good IF properly & sufficiently cured ,,, i suspect that isn't the case w/your very fine home as tony's responded,,, haven't seen them in our area yet. AAC products include blocks, wall panels, floor/roof panels, & lintels,,, 1 advantage's quick/easy installs as mtl can be routed, sanded, & sized on-site w/std bandsaws, hand saws, & drill bits


in theory, there's no difference 'tween theory & practice,,, in practice, there is
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if you hear it from a guy in the apron store, be VERY suspicious the mtl/method will work,,, when it time to build something together, they won't answer phones NOR help
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Old 04-25-2013, 10:03 AM   #4
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Cracks in AAC Blocks


What brand of blocks are you using?
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Old 04-25-2013, 10:55 AM   #5
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Cracks in AAC Blocks


I agree those look like typical shrinkage cracks. If you see cracking in the foundation (concrete?) then it may be a settlement issue.
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Old 04-25-2013, 02:18 PM   #6
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Cracks in AAC Blocks


I cannot speak to the block, but the mortar joints look lousy to me. Undersized, Voids, Untooled etc. etc. Very poor masonry work IMO.
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Old 04-25-2013, 04:27 PM   #7
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Cracks in AAC Blocks


Maybe "stuart45" will see this thread, he's pretty knowledgeable in AAC constuction............
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Old 04-25-2013, 04:55 PM   #8
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Cracks in AAC Blocks


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Originally Posted by jomama45 View Post
Maybe "stuart45" will see this thread, he's pretty knowledgeable in AAC constuction............
....but he's from Europe, I understand!....
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Old 04-25-2013, 06:01 PM   #9
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Cracks in AAC Blocks


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Originally Posted by tony.g View Post
....but he's from Europe, I understand!....
And so is this OP likely............

I didn't mean that as a "dig" btw when I said that weeks ago. What I was getting at is that a professional that had set his own eyes on the issue on site likely has a better diagnosis of the real issue vs. someone on the internet on another continent or even another country, or state for that matter.........
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Old 04-25-2013, 06:15 PM   #10
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Cracks in AAC Blocks


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Originally Posted by jagans View Post
the mortar joints look lousy to me. Undersized....
Thin joints seem to be normal on AAC blocks.
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Old 04-26-2013, 09:55 AM   #11
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Cracks in AAC Blocks


I have been doing a lot of research on various types of cracks in walls constructed by AAC blocks.. and as far my experience goes, such type of cracks are prominent in the region where there is drastic climate variations.
Secondly, the mortar used for AAC should be designed such that in any circumstances the strength of mortar should be less than the strength of blocks.
@Abhyudaya: I suggest instead of using 1:5, try using 1:8 mix design. Another point to be noticed is that OPC 43 & 53 grade cement should be strictly prohibited.
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Old 04-27-2013, 06:31 AM   #12
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Cracks in AAC Blocks


Quote:
Originally Posted by itsreallyconc View Post
for the rest of us ignorant oafs, aac block is autoclaved aerated concrete - wikipedia.org/wiki/Autoclaved_aerated_concrete - lite weight, pre-cast units w/no coarse aggregate - provides structure, insulation, fire, & mold resistance
Wow, I learn something from this forum almost every day. Call me old school, but AAC doesn't sound like a product I'd want to use.
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Old 04-27-2013, 08:49 AM   #13
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Cracks in AAC Blocks


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AAC doesn't sound like a product I'd want to use.
I don't blame you. It's been in use here in UK for years, as most buildings here are solid or cavity masonry construction.
Its like working with solid blocks of meringue. Bricklayers like them because of their low weight. They have good (relatively speaking) insulation characteristics and can be cut with a hand saw.

But a draw-back is shrinkage cracking. Like all concrete walls, walls of AAC block do shrink, but rather more than normal (dense) concrete blocks.
Partly that will be a function of the strength of the mortar, and sometimes allowing the blocks to get wet during construction.

In terms of load-bearing capacity, they are quite low on the scale of masonry blocks, though with careful design, multi-storey domestic structures can be built. One point builders have to watch when dealing with masonry construction are the bearing points for steel beams spanning on to walls. Thicker piers of dense blocks are often required here because of the locally increased stresss.

I know of many builders here who have stopped using them because of the problems involved.
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Old 04-29-2013, 11:30 AM   #14
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Cracks in AAC Blocks


AAC is a great product when applied properly. It gets its criticism from people who try to outright replace traditional cmu with it. That's where it all goes wrong. It may be installed by a mason, but that is generally where the similarities stop. It falls in line with spray foam. Just because it can be used everywhere doesn't mean it should under the umbrella of good building practice.
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Old 04-29-2013, 12:45 PM   #15
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Cracks in AAC Blocks


AAC is made in a wide range of properties, depending on the location and customers choice.

Usually it is based on density, with lightest having the best insulation and fire resistance, but lower strengths, so properties are dictated by the use and the needs preferred.

As you see on the photos, there are vertical striations on the faces because the individual block are wire cut from a large loaf or billet that is completely cured at the plant, so there is no curing shrinkage, but moisture shrinkage will depend on the exposure. The block is the photos were laid with a thick traditional mortar joint and not the thinner joinst suggested by the international experts. Usually AAC is made in smaller (block-sized) units, but I have seen 4" wall panels used in a home in Atlanta after the trusses were placed, but before any interior finishing. The product was also made in thicker wall panels for exterior non-bearing building walls.

The strength is really not too low, because I saw many 3 to 5 story buildings built in Europe using AAC with either brick of stucco on the exterior walls and plaster on the interior walls.

Dick

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