Essential Earthbag Construction - an interview with Kelly Hart

by: EJ on 07/16/2018
Posted in: Natural Building

I've always been intrigued by earthbag building and Kelly Hart's new book Essential Earthbag Construction: The Complete Step-by-step Guide is the perfect book to fuel my dreams of an earthbag root cellar.  In today's author interview, Kelly Hart answers questions about building techniques and shares some stories from his international work.


1) What sites are best suited to building with earthbags?  Which are border line and would work with some adaptations.  Are there any you avoid altogether?

The best sites for building with earthbags are those where the climate favors the use of the local soil as fill. This means that the climate is moderate enough to not require extra insulation to create a comfortable abode, whether building above ground or below.

Practically any site can be suitable for earthbag building if you can locate appropriate insulating fill material, such as crushed volcanic stone, pumice, perlite or rice hulls.

One should consider building an earthbag dome only in rather arid climates; otherwise there is the risk of possible leaks undermining the structure.


 2) When using polypropylene bags, do they ever decompose and cause problems?

Polypropylene is not degraded by moisture or most chemicals, but the UV in sunlight can rather quickly degrade this fabric. Therefore it is very important to assure that the bags are kept away from sunlight as much as possible, with tarps while not actually engaged in construction or good plaster as a final treatment. 

3) What kind of plaster do you recommend and why?

For interiors a natural earthen plaster is often used, or a lime plaster will provide a more durable and brighter surface. For exteriors I suggest using a lime or cement stabilized earthen plaster or a regular lime plaster. In situations that require durability because of extreme exposure to the elements, a regular cement stucco might be advisable.

4) There are a lot of photos from around the world in your book.  Can you share a story of one of your overseas trips that was particularly memorable for you? 


My most memorable overseas trip was one I took about a decade ago to Saudi Arabia. I was invited to lecture at the King's University in Jeddah about sustainable architecture in general. This was a real eye-opener to a very different culture than what I am used to. The Saudis were very gracious and welcoming, but I often felt like I was engaged in the Twilight Zone, where gender roles were extremely skewed.

At one presentation I made in a large auditorium, the entire audience appeared to be men, then I noticed several women seated at the far back on the last row of seats. After my presentation, as I was preparing to leave the stage, several of the women approached me with a few questions, which I answered.

Later I learned that these women (students from the women's University across the street from the men's) were actually not supposed to have been present in the auditorium, since they are usually shunted to a separate room where presentations are viewed via television.  But someone had neglected to reserve this room for them, so they were allowed to sit in the back. The staff member who had made this mistake was severely reprimanded because I should not have been able to make contact with these women.


Photo credit: Mark Stephenson

5) What makes using bags better than tires? Earthbags vs. Earthship.

The trouble with tires is that it takes a tremendous amount work to pound the soil into the tires with a large sledge hammer. And then once they have been packed and arranged into place on the wall they don't really form a nice flat wall, since there are all of the cavities that are created by the circular patterns being tangent to each other; all of these cavities then have to be filled with plaster and/or other materials to create a flat wall. A traditional Earthship design could be built way more easily using earthbags instead of tires.




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