aircrete vs. ferrocement



  • So I want to build a dome house (in a tropical climate), where sun, lots of rain, humidity, insects and earthquakes are to be considered.

    I really like the aircrete idea, however some local builders pointed out to me that ferrocement
    with a rebar structure would be more suitable. Offering both, better stability and flexibility of the structure, and it´s much better tested in terms of durability. Those domes can carry a lot of weight...

    Plus, there is always the risk that the aircrete blocks are not done the right way and you have no way to test their quality...

    Any thoughts on that?
    Thanks


  • Little Dragon Tamer Forum Facilitator

    Great post. Great questions. I'm glad to hear that you are questioning standard building practices - thinking outside the box - thinking for yourself.

    You want to build a dome. Domes appear to be good housing options for many reasons. Being essentially the strongest possible habitable type geometric structure, we have the option of using materials that don't need to be as strong as those used for making inherently weak geometric structures. Is a ferrocement dome of the same shape and wall thickness stronger than a aircrete dome? Absolutely. If the goal is to live in an above ground bomb shelter, then ferrocement is the better choice. And while my neighbor lives in his ferro-cement bomb shelter, I'll use the same budget and build 10 very safe, comfortable, aircrete domes of the same size. Ferrocement is definitely "much better tested" than aircrete in the sense that it is the popular building material. It is not better tested in the sense that it has not been tested as well - the consumer-industrial-capitalistic society tends to promote, research, and test those products that have the most profit making potential. Aircrete is to the building industrial complex, what herbs are to the medical industrial complex. Those who choose to build with aircrete are generally those who are not afraid to make choices for themselves - observe, orient, decide, act. Many others choose what is considered "well tested" - observe others, act.

    Concrete can be poured the wrong way also - I've done it. While it's true that there are volumes of detailed testing methods prescribed by the American Society for Testing and Materials (ASTM) whose instructions are meticulously followed by well paid scientists in white lab coats inside of multi-million dollar ferro-cement laboratories, no sample of concrete from your project will get tested there. In reality, we test building materials by feeling it, looking at it, standing on it, jumping on it, hitting it with hammers and cutting it with saws.

    Those are some of my thoughts on this topic.



  • Zander, thanks for your reply. This is very interesting to learn and no, I definitely don't need a bomb shelter :)
    But... can you walk on an aircrete dome? Or install a roof structure like on Steve Areen's dome?


  • Little Dragon Tamer Forum Facilitator

    @claudettn We walk on our domes frequently. We've not attempted to add a roof structure like Steve's. Depending on the mass of the roof structure, the dome needs to be made with appropriately thick walls and shape (see catenary dome) to accommodate. Our typical domes use 3.5" thick blocks. I think for now our focus is on creating affordable, practical, reasonable living spaces. But there is lots of room out there for exploring even more artistic, creative endeavors. I would suggest building a small simple dome first, then another larger one, try connecting them, then play with more advanced concepts like roof structures and so on.


  • Little Dragon Tamer Forum Facilitator

    @claudettn said

    So I want to build a dome house (in a tropical climate), where sun, lots of rain, humidity, insects and earthquakes are to be considered.

    Regarding sun: Aircrete is very insulative, ferrocement is not insulative. Most ferrocement domes are coated with a thick layer of spray foam insulation.

    Regarding rain, humidity, and insects: Aircrete and ferrocement perform the same in this arena. Both are cementitious materials that are not affected by water, moisture, or insects and do not support the growth of molds.

    Regarding earthquakes: My personal vote goes toward aircrete, though there may be room for some debate. Aircrete is well known for it's inherent flexibility. An aircrete dome wrapped with a polyesther fabric shell has amazing resilience to seismic movement. The dome complex I am most familiar with is near the epicenter of Hawaii's recent 6.9 earthquake, which was preceded and followed by literally hundreds of smaller quakes in the surrounding few weeks. During that period 4 and 5 degree quakes were considered normal daily occurrences, with 2 and 3 degree quakes being experienced up to several times per hour. As a result, some cracks (up to 1mm wide and up to 24 inches long) can be observed in the dome structure above the raw cutouts for the planned windows and doors. To be precise, I observed one such crack above each of these raw cutouts. The one window that was finished has no cracks whatsoever. Regardless of how earthquake proof a structure may be, there are no rules on how strong an earthquake may be. In a catastrophic event where a structure is overcome by an earthquake, I'd rather be in an aircrete structure because chunks of falling aircrete will hurt, like ouch!, but falling chunks of concrete sever, crush, and splatter.


  • Little Dragon Tamer Forum Facilitator

    Here is a great forum post about how the same concrete is made differently by various concrete companies. This post questions the common notion that concrete is strictly regulated. It questions the validity/usefulness of concrete "PSI ratings". To me this post supports my earlier statement that "in reality, we test building materials [including concrete] by feeling it, looking at it, standing on it, jumping on it, hitting it with hammers and cutting it with saws [or jackhammers]".


  • Major Contributor

    Is Aircrete strong enough, can you walk in it..

    Yes..

    If my entire 24' dome was the wet mixing weight it would be 55,800 pounds. Divided over the area of the
    8" thick dome wall is only 7.5 pounds per square inch.. Now cure out the water weight and consider that my test samples cure out stronger than 160 psi at 30 days... Yeah it's strong enough to walk on and not going to fall over...

    Now considering the tensile strength of the fabric at the equator.. Apoc 482S is rated 35 psi.. The circumference is 904 inches. The total tensile strength is 31,667 pounds. Using g a fabric rated 90 PSI would yeild 81360 points of tensile strength. Now how much weight of the structure transfers through via compression and how much stress is actually put on the fabric... I have no idea...