Stabilized adobe bricks (CEBs) curing in the shade

Stabilized adobe bricks (CEBs) curing in the shade


“In response to a recent post on the blog, I searched for Earthen Buildings East Africa to look for photographs and came across the following link:
http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1187&context=theses
[large file warning to those with slow Internet connections]

You may judge it worth publishing on your site as it, for a thesis, examines the properties of building bricks made from various materials for low-cost building in Africa but could be used anywhere as demonstrated by tests in central Tanzania with parallel results from California.

It, rather surprisingly, shows the “Best bricks for the Buck” are made from clay stabilised with lime, provided you protect them from rain and particularly floods. These are ideal for those who cannot afford or do not want to use cement.

Lime is the traditional stabiliser, used on the East African coast for 2 or more millennia, with dead coral blocks and coral rag.

I think we can regard lime as a sustainable material as, in Kenya, the major supplier uses their own plantation timber for firing the kilns.”
Tony

From the Conclusion of ANALYSIS OF STABILIZED ADOBE IN RURAL EAST AFRICA By Grace Ying Yu Chen

“Because flooding is not common in Itigi, the 7% lime with clay bricks, which performed well in all tests except water submersion, is recommended for future construction in Itigi. Using 5% cement+5% lime instead of 10% cement decreases the cost of bricks by 23%. Using 7% lime with clay instead of 10% cement decreases the cost of bricks by 61%. The 7% lime with clay mix is the most affordable choice.

Thanks to Tony for notifying us of this report. Our blog benefits greatly from reader contributions.
Note: Lime can also be used to stabilize earthbags where moisture problems are a concern.
Related: Eleven Earth Floor Methods


Comments

Lime Stabilized Adobe Bricks — 5 Comments

  1. As a mudbrick builder in Melbourne Australia we use no lime or cement in our blocks as the clay in our region is perfect when mixed with a little straw. By far the most effective render is one made from a mixture of river silt and fresh cow manure. As the manure is made predominately of cellulose, it bonds with the silt creating a plasticised render that repels water for up to ten years. This by far the most cost effective low impact type of construction. Using this render avoids de lamination from the bricks as they expand and contract at very similar rates.

    • Hello,
      I noticed you said “fresh cow manure”. I’ve seen online that if you ferment the cow dung for at least a few days (up to 6 months), it becomes more waterproof and more wear resistant. Do you know anything about this?

  2. Thanks a lot for posting this.

    Research such as this is very important and a necessary step along the way of optimizing materials for maximum benefit.

    There are other important steps that still could use some research.

    For example, is it more effective in cost/performance ratio to use the lime to enhance the plastering layers protecting an unstablized adobe wall, or to incorporate the lime into the adobe to stabilize it? A family is concerned with the total cost of the structure. Sometimes investing in the protective layer is more effective than investing in what should be getting protection so that it never encounters water in the first place.

    Does the entire wall NEED to be stabilized? If the first few rows of bricks near ground level are stabilized, and then unstabilized bricks are use to finish the wall to final height, how does the performance of that entire wall system compare to completely unstabilized as well as completely stabilized walls? Most wall structures encounter the biggest moisture threats near ground level. It may not be necessary, or even particularly advantageous, to stabilize the entire wall.

    I notice that during the waterjet penetration tests, that the unstabilized Clay (CEB) bricks performed just as well as (10% cement) and (5% lime/5% cement) stabilized bricks. Those three performed better than every other mix tested.

    This indicates that unstabilized bricks perform just as well as stabilized in a “splashback” or “rainfall exposed” environment. This seems to indicate that stabilizing areas of the wall that will not be subjected to flood waters may add no real value and add unnecessary cost.

    Unstabilized material did perform poorly in their submersion test, indicating that stabilized blocks which performed far better in the submersion test would provide substantial benefit to the lower parts of a wall that will tend to see the most flooding type of exposure.

    I submit that there is no real defense from flooding if a structure is nearly completely submerged other than simply building on higher ground in the first place.

    The most common type of flooding is a more shallow flood, such as a flash flood. Even more common may be improper grading of the building site causing water to pool near the foundation and base of the wall. Stabilizing the lower rows of brick should be more than sufficient to protect against these most common types of flooding.

    I suggest that the above information from this study should apply well to earthbag building as well, and I suggest that stabiling the first couple of rows of bags may provide sufficient protection against the most typical flooding events.

    I was VERY disappointed to learn that the Modulus of Rupture and Compression testing did not include any unstabilized samples. This absence taints the final results of the overall study because there was no control sample in the MR or Compression testing to use as a frame of reference with the other samples tested. The nature of their explanation for this oversight is that their unstabilized blocks broke apart during transport. This is an indication that their unstabilized adobe blocks very likely were not of high quality by adobe making standards. Yes, unstabilized adobe CEBs can be fragile, but they don’t typically just fall apart during transport if they are made well. Damaged blocks my not be uncommon, but having them completely fall apart as they described indicates a more general quality problem.

    I suspect that there was a fundamental flaw in the unstabilized bricks.

    NO SAND WAS USED IN UNSTABILIZED BRICKS.

    This factor draws into question the quality of all the unstabilized brick in every portion of the study. I know of no authoritative recommendations, nor of any common practice of using 100% clay unfired bricks in construction.

    Due to this fact, we cannot know for certain how the various percentages of cement and lime will compare to PROPERLY MADE unstabilized bricks, and that is the appearance of the question that the authors seemed to be attempting to explore.

    However, even with these serious flaws in their samples, I think the study still has a lot of good information and value in it.

    Great post. Thanks for sharing.

    • In most cases there is no need to stabilize the entire wall, whether earthbag or CEB. Common practice is to stabilize the lower wall up to 100 year flood line and/or one course above floor height. For deep snow, it’s good to stabilize the walls up to the snow height.

      You might also want to add some earth berming and 6 mil plastic around the base of the wall for an additional layer of moisture protection.

      Bill Steen has the best info on lime plastering. An entire issue of The Last Straw Journal was devoted to Steen’s lime plaster methods. Back issues are available.

      Unstabilized CEBs are brittle but should not fall apart if properly made. Adding some sand to the mix is standard. Clay binds the sand together. The sand increases compressive strength and hardness.

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