AAC Block construction experiences

[rkodal]

Hello All,

We are planning for group construction with friends, as of today we short-listed 2 properties 40x60 plots and now we are in process of understanding/choosing the construction materials for the construction estimation cost around 5000+ SQ FT.

I was searching on the net.. found that AAC Blocks construction is better than the regular solid cement blocks & cost effective, faster construction, requires lesser sand and eco friendly. I would like to know, Is anyone in the group explored with AAC or construction experiences ?

Thanks,
Ram

[civil88]

Hi,

I have started my house construction using AAC blocks from UltraTech. The product is called Xtralite.

All the advantages that you have listed are correct. In fact, if you inform the structural engineer before hand that you are going to use AAC blocks, he would keep that in mind while designing the structural drawings. This will also result in savings in terms of less steel, as AAC blocks reduce the dead load of the structure.

I have had good experience with using AAC blocks. The blocks are strong, light, consume less mortar between joints and also for plastering.

Their water absorption is also less. They have millions of tiny holes which are not actually in straight lines. So, even if they are exposed to continuous rain, it takes very long for the water to reach from one surface of the block to the other. When you drop them in water, they actually float!

I urge all the prospective house owners to consider this for walls for the obvious advantages and also for getting the satisfaction that we doing our bit for the society:
1. These blocks are made using flyash, which is an environmental threat in the sense that huge mountains of flyash are getting piled up near the Thermal power plants. If they are not used for making blocks they get absorbed into the atmosphere causing health hazards.
2. By not using red bricks we are helping the environment by letting it have the top soil useful for agriculture.

Do PM me if you need any further information.

Thanks,
Venky

[rkodal]

Thank you Venky. Sure I will do PM to you further information.

Meanwhile,
1. Can you let us know average construction cost per sft? & requires a highly skilled/trained labours to construct using this blocks?
2. Does this blocks requires out side plastering ?

In which area your house is constructed? If you do not mind, can we see your building sometime in the weekends?

Thanks,
Ram

[Naveenkpt]

There are many light weight bricks available in market and it will reduce cost with speedy construction.

[civil88]

Hi Ram,

1. I cannot give you Average Cost of construction per sft right now, as my house construction is still in progress. It does not require special/skilled construction. But the masons need to maintain the plumb and line very carefully. Even if they make a single mistake, it becomes obvious to the onlooker because the length of the block is 2 feet.
2. They do require outside plastering as well as inside plastering just like normal wall. Some people are avoiding inside plastering by going for putty application directly. But I feel it is not advisable. Outside plastering is a must to avoid seepage of water. Please use kabootar/chicken mesh jali at the junction of beams and walls, so that there are no cracks in the wall, especially on the external side.

My house is situated in Plot No 134, Confident Whitefield Oberon Layout, Adjacent to Mount Litera Zee School, Sadaramangala
Whitefield, Bangalore 67

Thanks,
Venky

[myhousemyhome]

I read with interest that some of our esteemed members here are keen on experimenting with AAC Blocks. I had researched this item for use on an external wall, and was also recommended their use by my Str Engg. However,he did add a corollary-- seeing that Quality of Masonry is poor in general, and scientific methods are replaced on-the-fly with traditional skill-based methods-- AAC expands when in contact with water. Cracks developing on external surface of wall-plastering will lead to water-absorption, and a worsening of the condition. This is typically noticed under Awnings and window-sills. Adequate details are available on the net. Click this http://tinyurl.com/ph7qgax. The story on environment protection is just that--a story, for obtaining sales. This product's manufacturing is energy-intensive, through autoclaving. Flyash disposal to address environmental concerns , has already adequately been achieved, by mixing flyash of good-quality (the operative word, about which we in India are provided no information on) into OPC, at a ratio extending from 15 % by weight to 75% for heavy structural compressive concrete requirement, obtaining finally what is called PPC. An option that I then considered, as an alternative to AAC, was Clay Extruded Bricks. Thanks.

[civil88]

However,he did add a corollary-- seeing that Quality of Masonry is poor in general, and scientific methods are replaced on-the-fly with traditional skill-based methods-- AAC expands when in contact with water. Cracks developing on external surface of wall-plastering will lead to water-absorption, and a worsening of the condition. This is typically noticed under Awnings and window-sills. Adequate details are available on the net. Click this http://tinyurl.com/ph7qgax.

Your Structural Engineer has put forth some theory, which as far I know, is not really substantiated well enough. 'AAC expands when in contact with water' is not correct. I have exposed my full load of AAC blocks in the mighty November Bangalore rains. The blocks did get wet, but there is no change in shape as claimed by your Structural Engineer.
Any external wall needs to be taken care of while constructing to take care of seepages, and AAC is no exception for that. If you add a Kabootar jali at the junction of beams and walls, the cracks are taken care of. Other than that there should not be any other seepage problems.

Your link, is very funny in that, the guy says cons and adds pros. Sample this:

Climates

Aerated concrete blocks are mostly beneficial in climates that have a big temperature fluctuations over the course of a 24-hour period. This is particularly for sunnier climates that yield a long period of hot days and cold nights. This is because of the high thermal mass that these blocks provide. The walls made from these blocks react similar to a sponge during the hot sunny hours and then releases the heat later when the temperature gets colder.

In fact, thermal insulation is one of the major advantages of AAC Blocks. They keep the house cool in summer and warm in winter due to the millions of pores they have which retain the heat/cold, for a long period of time.

I don't think the person who wrote that article is a qualified technical guy for the simple reason that there is no mention of the author's name in that article anywhere. Someone has rightly commented at the end of the article: "Where are the cons?"

Please do not spread wrong information, simply for the sake of it. This forum is meant for exchange of useful info and by that we mean, either you speak from your personal experience or quote a qualified technical guy, not some one who is either not giving the reason behind his blanket statements or some one who is not bold enough to write his name in the article.

[myhousemyhome]

Dear Members/readers

I had commented in this forum , stating that AAC is affected by moisture, and had reproduced a caution from a qualified Str Engg for the benefit of those interested in the product.This was not a biased opinion, as being labeled by some here.

I urge all interested people to read and research products and services that are introduced in the Market for their Magical properties, peddled by sales/marketing people, who are trained to unilaterally dismiss any voice of caution or negative experience about a product, by breezily dismissing all queries or genuine fears.

The Paper presented by Bohner&Odeen ( people with technical qualifications, I presume; And, bold enough to publish their findings under their name) in an International Conference on Durability of Building Material,is linked here, openly sourced from Public access to Google Books, page 110 to 112, Articles 4.3 onwards, in Part I, Paper 10 with the Title " Durability of Autoclaved Aerated Concrete"( AAC). http://tinyurl.com/nde6czf

If I had waited for personal experience to educate members, as seems to be the operating logic pressed upon others by some, then I would remind them of Otto Von Bismarck's Quote “Only a fool learns from his own mistakes. The wise man learns from the mistakes of others.”
Please be wise and take calibrated decisions.

[civil88]

Dear MyhouseMyhome,

I urge all interested people to read and research products and services that are introduced in the Market for their Magical properties, peddled by sales/marketing people, who are trained to unilaterally dismiss any voice of caution or negative experience about a product, by breezily dismissing all queries or genuine fears.

With respect to AAC, it is only logical that users have fears of accepting a new product how much ever, good it actually is or supposed to be. At the same time, we need to evaluate the pros and cons before fully embracing it.
To trace the evolution of AAC, let me first quote the excerpt from the online reference given by you:

Excerpt from article

AAC Article.JPG (54.75 KiB) Viewed 12651 times

As can be seen the technology is there from as early 1960's or even before. In India, it has picked up in the last ten years. If the AAC blocks technology is so bad, why would a giant in the Construction industry like L&T promote this product. FYI, AAC blocks are being used more and more now-a-days by more and more people, not only in major cities but also in towns.

Earlier, when Cement hollow and solid blocks came newly, people did not accept it for a long time. Now more than 50% of the constructions use them. They have replaced bricks to a large extent.

Coming back to the article. They are several things to note:
1. It was done on industrial buildings.
2. It was done on buildings built 3 decades ago, where the walls were either not plastered or if plastered, with thin plaster.

So all their findings are based on these sample industrial buildings.

Please do not quote out of context. If you do not want to embrace AAC technology. It is absolutely fine with me or any body in this forum.

For the sake of quoting you have quoted from a US forum site, which does not have even half the meaningful contributions that we have in this forum.
Today's quote is from a book written in 1999. Technology evolves so much in a decade. AAC has evolved so much that qualified technical people (I will give the details in the end) have certified this technology and have been advocating the use of it in all their projects in multi-storied residential and commercial complexes all over South India including Chennai, Bangalore and Hyderabad.

If any body has any more reservations about AAC blocks, they can speak to this Structural Engineer, Mr. Pratap and get their doubts clarified.
M/S Continental Designers, Hyderabad. If you google you can get their full details.

[hrsn]

Does AAC walls need any special plastering such as water proofing?