Thermal Performance Data on an Earthbag Dome

Awhile ago, I wrote to you asking if you had any recommendations for stabilizing our 14′ (inner diameter) scoria dome tank house which had started to fail as a result of the bags breaking down. I wanted to give you an update.

Beldar
We paid a crew last November to shotcrete it inside and out, and it is performing very well. I just wish I knew whether it was the mass of concrete or the insulation of the bags. Probably a combo. I am interested to see how it performs once the mass has heated up a bit this summer.

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Does Insulating Paint Really Work?

For many years I have wondered about the effectiveness of various products that advertise that they can insulate roofs and walls by simply painting them! The technology is said to stem from the science (developed by NASA) of protecting space vehicles by coating them with tiny ceramic spheres that reflect heat, so that they don’t burn up when re-entering the atmosphere. Some products consist of an additive for paint, while others are specially formulated paint.

When I realized that I wanted to insulate the 1940’s adobe house I had bought, I began to wonder whether this might be a simple solution to accomplish this. In researching this possibility I discovered that there were conflicting opinions about whether such a paint could work. The manufacturers claimed that many tests have proven their effectiveness and there were some testimonials from individuals or businesses that made similar claims. But I couldn’t find any independent studies that I considered actual validation of the concept.

Not being willing to proceed blindly with painting my entire house with expensive paint on the assumption that it would improve the thermal dynamics of my completely thermal mass walls, I decided to conduct an experiment that would accurately inform me exactly how effective the paint might be. I conceived of a situation that would simulate the thermal mass walls that were left open to the ambient atmosphere over several days. There would be one setup painted as prescribed with the insulating paint and then a second control setup that was identical, except without the insulating additive. Embedded within each of these would be a wireless thermometer probe to keep track of the separate interior temperatures.

painting

I found some perfectly uniform 16’X16″X3.5″ concrete blocks for sale at my local building supply store quite cheaply, so I bought ten of these. Next I acquired the insulating additive (Insuladd was the brand name) and used some exterior latex paint that I already had on hand. I thoroughly mixed the additive to some of the paint and kept some of it in its original form for the control. Then I painted half of the concrete blocks with the insulating paint and half with the control paint, applying two coats of each.

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First Earthbag Shake Table Tests Create a Computer Model

Results of earthbag wall shake table test at Dartmouth University.
Results of earthbag wall shake table test at Dartmouth University.

“How much reinforcement do straight wall earthbag buildings need for earthquakes?
Engineers can’t tell without test results. Until this year no one has tested earthbag on a shake table, since full-size testing could cost between $10,000 and $15,000 USD.

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Proctor Soil Compaction Test

The Proctor Test is used to determine the optimum moisture content in soil, and can help create stronger earthbag and rammed earth structures.
The Proctor Test is used to determine the optimum moisture content in soil, and can help create stronger earthbag and rammed earth structures.

“The Standard Proctor Test is a laboratory test used to determine the optimum water for a given compaction energy, for a given soil. The graph illustrates the results obtained from a Standard Proctor test.

The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density. (Compaction is the process by which the bulk density of an aggregate of matter is increased by driving out air.) The term Proctor is in honor of R. R. Proctor, who in 1933 showed that the dry density of a soil for a given compactive effort depends on the amount of water the soil contains during soil compaction.

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Shear Strength Wall Test Report

Test description: Shear strength of plastered 4′ x 4’/ 1.2 x 1.2 m bag wall (15″ / 38 cm thick) of weak cohesive soil with barbed wire; Materials: solid poly bags, tamped subsoils of silt and clay, lime and earthen plaster Abstract: Earthbag is a growing sustainable building technique that is increasingly desired in the … Read more