Although not necessarily required for earthbag building, stabilizing soil improves water resistance and compressive strength, and speeds drying time. Since 1978, Istanbul Technical University has been researching a technique called alker technology or alker construction. Basically it’s just soil stabilized with lime and calcined gypsum (plaster of Paris). The following summary is taken from their websites.

Comparison:
Traditional earthen construction: preprocessing, grinding, sieving, setting the soil aside, 30% clay
Alker construction: preprocessing is not necessary, 10% clay

Ingredient/% by Weight
Soil/100
Gypsum/10
Lime/2
Water/18-20

Traditional earth construction
15-21 days strengthening
curing area
water sprinkling
rain protection

Alker construction
20 min. strengthening
no curing area
no water sprinkling
no rain protection

Drawbacks:
No building system is perfect. Although more moisture resistant than plain earth, Alker stabilized soil will absorb moisture, so your design must take this into account. Either raise the lower wall (ex: higher foundation), add waterproofing sealant and/or protect walls with wide roof overhangs. Note the rapid set time — you have to place the soil within 15 minutes. Plus, there is the added cost of materials.

http://www.kerpic.org/alker_technology.htm
http://web.itu.edu.tr/~isikb/yemenbildiri01.html

Note the similarity to Cast Earth at Wikipedia that explains the cast earth formula is proprietary knowledge, but the alker method is not. The major advantage of cast earth is greater working time that enables continuous pouring of an entire house, and then rapid strengthening so forms can be removed the same day.


Comments

Gypsum and Lime Stabilized Soil (Alker Technology) — 5 Comments

  1. Wondering if there is a recipe for lime stabilized soil, or Portland stabilized soil that is best for earthbag building.
    Like what type to use and how much per wheelbarrow of earth?
    I know the local mega-orange hardware store sells a “type s” lime, is that what I should use? I don’t seem to have as much clay in my native soil as I wanted, and a lot of the areas where I want to excavate for earthbag building were “filled” with a sandy fill as part of the originial house construction.
    Is stabilizing the soil with Lime a better option than adding portland cement? If not, how much Portland should I be using.
    Sorry for the simplistic questions, but I do appreciate all the help I can get :)
    Richard

    • It partly depends on where you live and your local conditions. Most often earthbags don’t need stabilizing. It’s a lot of extra mixing and expense, so only do this if necessary. Or maybe you can get by just stabilizing lower courses. (Ex: areas with heavy wind driven rain or deep snow would benefit from some stabilized courses.)

      The percentage of lime or cement, and which is best, is based on your soil conditions. Cement works best with sandy soil; lime with clayey soils. Do some experiments with sample bags. Wait two weeks or so, spray with water, soak in water, cut open and examine them, etc.

      Lime gains strength more slowly than cement, but is less detrimental to the environment. Plus, lime allows moisture to pass through the wall.

      • The primary company mining and selling scoria in that region is Colorado Lava. Their number is 800 528 2765. The mine is just outside Antonito, Colorado, on the New Mexico side of the border with their main offices in Illinois.

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