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    Understanding Adobe

CROCKER LTD  
Architectural Conservation  
2019 Galisteo Street, Suite N-10 A  
Santa Fe, New Mexico 87505  
505/ 982.2448  •  877/ 982.2448  





Waiting for the Big One
Edward Crocker

An architect friend in San Francisco recently asked if I would undertake a "small" project on the outskirts of Riobamba in Ecuador. Being an easy mark, and having a four-year old daughter who my wife, Ann, and I are determined to expose intensely to a second language, I incautiously responded in the positive. So we spent six weeks in the central highlands, at about 1.5 degrees south latitude, surrounded by active and inactive volcanoes, just before Christmas.

I love building with adobe. I donít mean being a contractor, which has its ups and downs, but sinking my hands in the mud, spreading the mortar out in a thick, luscious layer, and pressing the blocks in until they seat, firmly and with the promise that they will provide a comforting and safe retreat. That was a big part of what this project was all about for me. The rest involved a bit more responsibility; building a training center intended to house up to 25 guests at a time in one of the most seismically active zones in the world.

The site is on a farm, about four acres in size. The building, a quarter circle of about 2500 square feet embracing a small hill, will be used to advance the promise of organic agriculture, potable water systems in rural communities, earthen building technologies and small-scale marketing strategies for indigenous peoples in the region. One of the things that I find most compelling about the project is that though it sounds a bit idealistic, with a mission statement that reads as though it comes from the not-for-profit world, it is private enterprise, pure and simple. The owners, Marco and Marta Andino, are a couple with 15 years of community development experience with SwissAid who have had a parting of the ways with that agency. They are betting their lifestyle on the hope, not unreasonable based on their research, that national and international organizations will pay for the use of the facility and for the commitment and experience the Andinos have to offer.

Ecuador has, as most places do, a long history of building with earth and, as noted, doing so in a very unstable area. My approach to the project was to first assess the local soils and then determine which of the local building technologies was most appropriate. The region has thousands of examples each of rammed earth, adobe and wattle and daub, many clearly dating to the Nineteenth Century and before. That, of course, implies that they have survived many, and some quite significant, seismic events.

Unfortunately for the Andinos, I was quick to eliminate the soil on the farm as a candidate for rammed earth, their presumed method of building. The soil was nearly pure silt, almost no clay and the aggregate was the odd pebble. When we built a test wall, by the time we got to the second 8-inch lift we couldn't compact; the soil became springy and walking on it was like stepping on a sponge.

Just to verify to everyone that the soils wouldn't work, we made some sample adobes with it and had compressive strength tests done at the local polytechnic institute. The results were surprising Ė the lowest I have ever seen - with a bearing capacity of 56 psi. An average New Mexico adobe will test between 400 and 600 psi.

While all of this was going on, Ann and I continued our survey of local building methods and materials. Our first significant "find" was in a little town called Chambo where the modern regional building material of choice, low-fired bricks, are produced. There are numerous small manufactories that convert the rich local black clay into fragile, friable red bricks. We weren't interested in the bricks, except in their incipient state -- as adobes before they went into the kiln.

We got really interested when we were quoted the price: 3½ cents (US) apiece!

Next stop: Licto. This little community is famous for its light, fluffy biscuits: Those are good though I prefer their antithesis, Walker's shortbread. Our attention, however, was diverted from the pastry by a series of buildings, seemingly dating to the mid-1800s based on architectural detailing, constructed of bareque, or bahareque depending on whom you asked.

Bareque is an elegant solution to a serious threat. Where wattle-and-daub has always seemed to me a little insubstantial (though spectacularly successful in earthquakes) and only good for one-story buildings, bareque by contrast has some heft, and is suitable for multiple living levels. It is, in brief, a composite wall with mud, often adobe, entrapped in a cage of wooden slats. When the shaking begins, even if the mud fails the blocks of masonry are impounded.

We saw many, many examples of bareque that had clearly been through tremors that had left the earthen walls cracked and, in some cases, nearly disintegrated. Still, the walls were standing and had been repaired by the addition of fresh material.

So that is what we did for the Andinos. We used lumber sawn from the local (actually alien) weed tree, Eucalyptus, for upright posts affixed to the foundation and as horizontal slats to contain the wall at one-half and full height.

I used to be in the water well drilling business which is a highly intuitive enterprise. Science can give you a few pointers, and experience helps lead the way. In the end though, it is the sixth sense of the driller that tells him where to drill, how deep, and how best to develop what he cannot see.

I am trusting those same instincts when I state my faith that when the big one comes to Riobamba (and it is about due in its 110-year cycle), that this building will stand. I would be foolish to think that I can make any structure earthquake-proof, but I believe I am on solid footing when I say the building is earthquake-safe. Even if the tremor hit at 2 AM, if the occupants have 45 seconds to come to their senses and get out before anything heavy falls, it will have been a complete success. It will be superlative if it works out that they could have slept right through it.











Crocker Ltd
2019 Galisteo Street, Suite N-10 A  •  Santa Fe, New Mexico 87505
tel 505/ 982.2448  •  fax 505/ 995.9877
info@crockerltd.net
toll free 877/ 982.2448



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