Adobe/Cob vs. Concrete—Back to the Future?

Screen Shot 2018-04-27 at 6.29.30 PMBy Kary Vannice

Concrete is the dominant building material used in Mexico, much of Latin America and many other regions of the world. Why? The cost is relatively low, and with the use of forms, one doesn’t need a lot of technical or architectural knowledge to build a sufficient dwelling. However, while the cost of a bag of cement required to make that concrete may be nominal—making it easily accessible to nearly everyone wanting to build a home—the hidden cost of cement production is high!

The cost of cement

The main ingredient in Portland cement is cement clinker, which is produced by heating limestone to 950°C (1758°F). It takes a lot of energy to burn something at that temperature. To achieve such high temperatures, the fuel source is generally coal, and a lot of it! In addition, massive amounts of electricity are needed to crush the raw materials into the fine powder we know as cement.

Current estimates say that raw energy represents 20-40% of the total cost of cement production. Cement production is also a source of toxic CO2 emissions. And some news reports and government agencies claim that the end result is a toxic cocktail that can be harmful to humans.

Is it possible there is a better way? What did people do before the advent of cement in the late 1800s?

Cob/adobe and indigenous builders

Well, ironically, the precursors to concrete, adobe and cob, are now sometimes called “survival cement.” They are all-natural mixture of clay, sand, straw (or other fiber) and water; adobe is usually formed into sun-dried bricks, while cob is built up in layers.  When mixed in the correct proportions, the resulting material is as strong and durable as concrete, but with absolutely no additional energy needed for production, except the man- (or woman-) power to harvest and mix the ingredients, of course.

Indigenous tribes all over the world have been using these mixtures for millennia to construct temporary dwellings, and multi-story permanent, still standing, structures, including some of the buildings at the Neolithic Mehrgarh site in Pakistan, which were constructed in 2600 BC. In fact, adobe/cob is still the primary building material for over 30% of the global population.

Both the Maya and the Aztec cultures used earthen building techniques, and they are still used today in many rural areas of Mexico. However, where this was once the dominant form of construction, much of the skill and knowledge about this type of construction has been lost.

It’s no wonder the indigenous people of this region favored these materials. Not only can they be easily found in nature, and are easy to mix and build with, but they are also much “kinder” and cooler to live in than concrete houses. Adobe houses do not absorb or radiate heat at the same rate that concrete houses do. They stay much cooler during the day and slowly radiate warmth during the night, but because they don’t get as hot during the day, they maintain a much more consistent and pleasant atmosphere inside the home. Add to that that cob homes are often finished with thatched roofs that allow excess heat to escape, and you have an ideal dwelling for this climate, which is exactly the way the Aztec people made their homes.

A disappearing resource?

Why would such a thing fall out of favor? Well, it’s probably a factor of time. It takes much more time to build an adobe or cob home than it does a cement one. Cement dries quickly and can be mixed in gas powered machines, adding to the amount of energy expenditure needed, I might add.

The mixture for the “masa” for adobe and cob is made by hand, or feet, as the case may be. Building a home this way is usually a community affair, calling on the good-will of neighbors and family to pitch in and get their hands and feet dirty. The traditional way of mixing the ingredients is to combine them in the correct quantities on the ground and add water while mixing it all together with your feet. Once the proper consistency is achieved, the mud is either formed into blocks to make adobe, or simply stacked in place to make cob; cob is essentially monolithic adobe.

The process takes time, but in the end, more than a house is built. Bonds of friendship and community are also built. Stories, songs, laughter and maybe even a few tears are shared as builders stomp and squish the earth and water into the perfect earthen cement. And, in the end, every hand leaves a little bit of itself behind in the making of it.

Maybe that’s the real reason it’s called “survival cement.”  Any home built like this is going to survive because everyone who had a hand in building it is now invested, not just in the survival of the structure itself, but the family structure that dwells there, and surrounding community structure, as well.

Perhaps more important than the detrimental environmental factors, these human and community aspects should make us reconsider the building materials and techniques we use in modern day construction.

 

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