Failed Plaster on Dome — 6 Comments

  1. Mike, Owen just referred me to this link regarding earthbag building in Haiti. I am a straw bale builder/plasterer with no experience with earthbag building, apart from some wonderful books in my library at home. I have been plunked into a setting in PaP where there are some inexperienced (although well read and well intentioned) earthbag builders building a new washroom dome. They used unstabilised earth in the tubes, and we are at the point of figuring out plaster. Owen suggests cement- I’d be curious to know more about the coconut husks and the woven palm material- can you clarify what you mean?

    We do have some straw here on site, which we may be able to purchase for use as reinforcement fibers, but has anyone ever used bagasse? Shredded poly bags have also been recommended- any thoughts?


  2. This is a very good example of how necessary it is in green bulding, to know, understand and respect the characteristics of the locally available construction material ( in this case earth and its components).

    Earthbag building will not be the same everywhere or in all climatic conditions. It is so important to take a little time to study your local environment, its soil, etc, understand the characteristics and make the necessary adjustments BEFORE construction.

    I love the idea of building with earth, for many reasons amply discussed and talked about on this blog. The end result however of all these is a humbling experience of respecting your environment and how it works.

  3. More pictures would insure I am accurate but here is a first pass. The coating was applied too watered down and was allowed to dry to fast with out hydration. Second No reinforcement, Grass, straw, cloth strands, wire. These small fibers or connectors hold the shell together at the smallest point, in addition anything that holds water will release it during the set up phase in the concrete the concrete needs to say hydrated. No reason to blame anyone or the method you just need some simple process instructions – Do you know who built it – I will help them prevent it again. I cant see where the picture is taken from or the scope, or the structure in general. recommendations – A) for temporary protection cover with large soft leaves, blue tarp. B) then remove damaged areas, Break up this material 3/8 and smaller, removed and use as aggregate in new material. if in hati use chopped up coconut husk as a add mixture to make a blanket type covering material, use a weaved palm fron blankets directly on the bags to keep the layers of concrete shell consistent in thickness.

  4. If people are going to use cement, it must be used properly. I think “stabalized” earth for an exterior plaster is a bad idea. It is also unwise to use portland cement on a largely earthen structure . Think about the variability of settling time. Were the bags wet when tamped and applied. Is the clay content in the bags very high? IF the answer to these is yes then one should not use cement because it will inevitably crack and appear unappealing. No Dome in the tropics ought be plastered as the primary water proofing membrane. IT is SO important to keep the moisture content right when building any dome or strait walled structure, especially with less then ideal mixes. Too much clay and the wall will “move” when tamped. If rain saturates the building it can be less than ideal.

    Perhaps in areas of haiti with high clay content they use something like.) 60 pulverized rubble or chipped limerock X 40 HIgh clay soil) That might work to make the wall stable

    Ceramic Tiles. Yes. Roofing Tin Yes. Thatch Yes.

    I think we need to compile a “best practices manual” There is much new research that is not available in one text or document. This site is great, but often times people do not know where to begin with all of the posts. Some minds need organization!

  5. This project is worth thinking about.
    Cement needs decent sized aggregate to bind with, and this clay did not include it. Usually cement stucco is sand and Portland cement. Portland and clay is not the same.

    Also, I didn’t notice any fishnet or chickenwire in the plaster. I wonder how much that kind of reinforcement (which we’ve been considering a basic requirement for all construction in seismic areas) would strengthen the plaster.
    I’m about to start some experiments to test how heavy or expansive a clay can be used in the bags and still work with cement stucco. If an expansive clay gets damp it will swell. This would crack off the cement stucco, causing more wetting and more cracking.
    I’d love to hear if it was an impact point that this started on, and whether any swelling of the clay in the bags was involved.
    But for a heavy clay this is the most flexible and thus long lasting covering I’ve had recommended:
    1. Use an earth plaster as infill
    2. Then add 2 layers of lime plaster (earth in the first one and a more standard lime plaster with just sand in the second coat)

  6. Michael Reynolds of Earthship Biotecture does not allow this sort of problem to happen. In order to call your rammed tire home an “Earthship”, you must meet their strict criteria.

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