Autoclaved Aerated Concrete

Disclaimer

Autoclaved Aerated Concrete

A number of people have asked me how I found Hebel (aerated concrete) as a construction material.

First I should add a further disclaimer: this page contains only my personal opinions, and it has nothing to do with my employer, the University of New South Wales. They employ me for my expertise in computing-related areas, and neither they nor I claim any expertise in building. If you pay any attention to anything on this page, you do so at your own risk, and should rely on your own or other expertise to assess it.

Secondly, my opinions are essentially about the material, and not about particular manufacturers. For the record, I used AAC manufactured by CSR- Hebel, and found them very helpful, and their literature on the material was great, but that is probably also true of other manufacturers. I have absolutely no commercial relationship with CSR other than having bought their product, and no personal relationship beyond the normal friendly relationship that has built up with contact with their representatives.

For the owner builder, I think AAC is superb. I found it easy to work with - far easier than brickwork, it's simply a matter of care rather than skill. Prior to building what is a pretty large and reasonably complex house, my only building experience was a couple of garden sheds and lining a garage. While building the house has been a pretty slow experience, I haven't hit any significant problems. But there is one very important caveat: you really have to follow the manufacturer's guidelines to the letter. There are too many ways things can go wrong if you just treat it as brickwork. Since I've worked with computers for about thirty years, I'm used to being precise and following instructions exactly. It that doesn't describe your personality, you may not find AAC such a good material. Most importantly of all, don't treat it like concrete blockwork. Even though AAC looks a lot like standard concrete blocks, its physical properties are very different. If you use standard blockwork techniques, you will almost certainly get serious cracking.

In terms of the finished product, the house is very comfortable, the walls have a good "feel", and the insulation is first rate. It already works well as house, despite the fact that we don't yet have the verandahs which are an important part of the overall design. Despite the reasonably cold Winters (for Australia) - we're at approximately 1000 metres - our only major heat source is a big cooking stove in the kitchen. That was enough to heat the top floor for virtually the whole of last Winter - we used portable electric heaters in the farther rooms maybe ten times (and we didn't even have all the curtains up).

I haven't mentioned the most important issue for us: the house is structurally virtually fireproof, as not only the walls, but also the intermediate floor and roof, are AAC structures. And for added security, there's a fire refuge - no windows, and the door is a one-hour fire door.

I used 200mm blockwork for the external walls, and 150mm for the internal supporting walls, with steel framing for non-structural walls. The roof and mid-floor are 200mm panels, except for the wet areas which used 150mm panels to permit a contoured floor. The ground floor is a slab. We topped the floor with a levelling compound and parqueted it (except for wet areas, which are tiled). We used whiteset on the structural walls and gyprock for the non-structural walls and ceilings, with the external walls being bagged in the manufacturer's render. All of these worked well, though the external render was a b.... to apply (I've been told that some other brands of render are better to work with, but can't vouch for this; I can definitely say that the internal whiteset - from another supplier - was much easier, despite the fact that we were going for a much smoother finish, and that whiteset has a reputation of being harder to work with than render).

I've also had limited experience with the use of the wall panels (a friend's house). These worked well and were very quick, but her Dad was a retired builder, and was able to solve some tricky problems because of his experience. If, like me, you're a near novice, the blocks might be a better bet.

If you're thinking about AAC, and would like to talk it over, drop me a line trough the email below.

Best Wishes
Bob McKay


Email: rim@csadfa.cs.adfa.edu.au
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21/4/1999