Saturday, April 25, 2009
To Adobe or not to Adobe
Adobe elicits the kind of rhetorical rapture you don't generally hear about other construction materials like, say, cement blocks or aluminum siding.
"You can feel the warmth, the spirituality, the charm. It radiates! It has a round and soft feeling," one New Mexico builder raved about his adobe houses.
Close your eyes and adobe construction starts to sound like a cross between religion and sex, with a little yerba thrown in for added thrills.
Part of adobe's charm is its antiquity, like, as far back as anyone can remember. The pharaohs supposedly used it, and more recently so did Native Americans. New Mexicans seem to love the stuff and indeed Santa Fe architecture has been so adobified the city could be renamed Adobeburgh. The locals find it enchanting, though after a few days there, Stew and I found it boring. Adobe gas stations?
The recent rage over sustainable construction has given adobe added cachet. Its main ingredients are nothing if not sustainable and renewable: dirt, straw, a little water and some manure (the latter recently upgraded to asphalt to give the bricks added stability). You mix them, pour the stuff into forms and let it dry under the sun, another plentiful commodity in San Miguel. Pretty soon you have adobe bricks.
Just out of curiosity Stew and I went looking for the local adobe plant, about 15 miles out of town. The driving directions we got were typically Mexican--vivid, detailed and nearly useless. Next to a huge chicken farm? Nope, no adobe factory in sight. Across the road from a pig farm by a line of trees? Not there either, and by the way, those are horses, not pigs.
Finally, after 45 minutes of driving, we found the adobe emporium in the vicinity of some sort of a farm facility that may have contained pigs, chickens or goats. We couldn't tell for sure, so any one the three or four guys who gave us directions may have been right. Or maybe they were making things up and taking us for a ride.
A large man wearing a rancher hat and a nylon backpack, approached our truck and inquired about the nature of our business. I said we wanted to see how adobe blocks were made. "Imposible," he told me. We had to check with the boss first and he wasn't around.
The guy's secrecy and nervousness seemed amusing. After all, the facility was hardly an Iranian uranium processing plant. There was a pile of straw, another one of dirt and then a shed with open sides shielding piles of adobe blocks underneath. So much for the secrets of Mexican adobe-making.
Our decision to use adobe blocks to build our house came after some research and discussion with the architect. Ultimately it was equal parts aesthetics and our desire to build an energy-efficient home.
The almost universal building method in San Miguel is a skeleton of columns of concrete and rebar that holds up a roof also of reinforced concrete. Common red brick is then used to build the walls in between the columns. These bricks, known as tabiques, are cheap--about 10 cents apiece--and often sold from open trucks waiting by the side of the roads.
But at the hands of skilled Mexican masons, the lowly red brick can reach astonishing levels of beauty and craftsmanship. Many San Miguel houses have bóvedas or domes made out of bricks placed in concentric circles and capped with a nipple-like cupola with windows to let in light and air. The pattern of the bricks can be lineal, herringbone or a dozen other variations. The mystery of bóvedas is how the masons don't use any frames or other supports to hold up the bricks while the structure goes up and the mortar dries. Row after row of bricks goes up and then... I have no clue how those guys do it.
The advantage of brick is its low cost and ease of use. You can cut a local clay brick by whacking it with the side of a trowel. Half the adult men in San Miguel probably know how to build a brick wall, though applying the top coat of cement and doing it well is a far more specialized trick.
Brick, however, is a lousy insulator. During the summer, brick and cement houses seem to stay relatively cool, though the concrete roofs can retain the heat making bedrooms uncomfortable at night.
For Stew and me, the real downside of brick construction comes in winter when walls seem to be perpetually cold and clammy. Heating devices, most often gas fireplaces, fight with the cold brick walls but many rooms never seem to get evenly warm. That and the usual thin, single-pane windows make for very energy-wasteful structures.
Another option fast gaining in popularity in Mexico are AAC (autoclaved aerated concrete) blocks, which are lightweight, porous concrete blocks. Also called Hebel blocks, they have excellent insulating, sound-dampening and fireproofing qualities, all derived mostly from the air bubbles trapped in the concrete. Building crews have to learn how to work with the blocks, which are joined with a special adhesive, but once they master the technique the building goes up very quickly.
Drawbacks, yes, there are a few. One is cost, roughly about 80 cents a block according to our architect, some of which presumably can be recouped by the faster construction and savings in labor. Some enviros also point their collective finger at the high "embedded energy" in Hebel blocks. Compared to common brick, it takes a relatively high amount energy to make the cement, bubble it up and then heat it to get the finished product. It doesn't sound like a very sustainable building material.
Yes, but Hebel blocks give you much better insulation--and energy savings--than brick. Wouldn't that recoup the energy that went into making the Hebels?
Oh, boy. Now we're wading into the "six one way, half dozen the other" dilemma that you get into if you drag out some of these environmental computations and masturbations far enough.
No such fancy-schmantzy problems with ol' adobe blocks. Just dirt, straw, sun and the manpower to pile them up neatly to make a house. Embedded energy? Huh? Unless you count the gasoline for the truck to bring them to the worksite, there is none. (Hebel blocks, on the other hand, have to be shipped from a Monterrey plant in northern Mexico.)
Adobe houses are legendarily comfortable; inside temperatures remain within a narrow range throughout the year. The trick is adobe's ability to absorb heat and then release it at night. During the winter that locks the heat inside the living space; during the summer the reverse takes place, keeping the place cool. Or so goes the theory.
The adobe blocks in San Miguel are approximately 14" long, 10" wide and 4" thick and cost about 50 cents. I haven't actually weighed one but they feel like 10 pounds each and very dense. They are brittle and workers seem to handle them gently. Adobe is easy to cut or trim with a wood saw, a machete or other sharp tool.
We had the choice of leaving the outside adobe exposed or covering it with a top coat of cement. Stew and I opted for the exposed option, but with a sealant that gives the adobe a richer, darker hue. The sealant keeps the blocks from disintegrating under the rain and it has to be reapplied every two years.
Why exposed? We liked the earthen, more traditional look--particularly its expected contrast with the more modern contemporary details of the house--and the fact adobe will help the house blend in with the natural surroundings. In fact, from a distance, and even up close, the house blends in seamlessly into the landscape despite its bulk. We like it.
This is a shift for us, who started wanting to build a somewhat wild-and-crazy modern house, with some bright colors to boot. But the landscape surrounding our land ultimately won us over.
The cost of adobe was another "six one way, half dozen the other" deal. Piece by piece adobe is cheaper than Hebel blocks, but it goes up considerably more slowly. Particularly with an exposed exterior, quite a bit of cutting, fussing and finishing is required to put up an adobe wall, and judging by the scrap piles there seems to be quite a lot of waste. Our house has rounded corners which adds more chipping and trimming of the adobe blocks.
The extra work is manageable in Mexico because labor costs are very low compared to the U.S. I can imagine that building a fussy adobe house in New Mexico or Arizona, using $15- or $20-an- hour masons, could run into some serious money. Here our architect also specified inexpensive red brick interior walls to further reduce costs.
So our adobe abode is going up, though not as fast as we would like. There is a very warm, earthy feel to the stuff, accentuated by some of the curves the architect built into the design. A soft feeling, if you will.
Yeech. I'm starting to sound like a New Mexico housing developer.