Thursday, April 2, 2009

Stuck in a hole

And a big hole at that. Cost overruns and delays are inevitable and two months into construction we've already been hit by both, caused by the construction of our extra-large rainwater collection system.

Was it actually necessary? Is it worth it? I must confess that I've had my doubts. Stew insists it will pay off in the long run.

As I have mentioned in previous blogs, we envisioned a cistern that would hold approximately 130,000 liters, or 34,000 gallons of rainwater. According to other local folks who have rain collection systems, that amount should carry us through an entire year without too many water conservation acrobatics. Our architect, who has quite a bit of experience building sustainable homes says we have enough roof space to collect 188,000 liters of rainwater in a normal year. Because of global warming (or whatever, don't want to start an argument about that with any Republican relatives and acquaintances) rainfall in San Miguel has been unusually heavy during the past two years.

We figured we would save on excavation costs by neatly placing it under a terrace that cantilevers off the living room. That would give us a wide but relatively shallow cistern, about seven feet deep. It might even save us money, we figured, because we would not have to dig a much deeper hole.

Then we ran into geology, soil and rock formations and other kinks. The top layer of black soil, about 18 inches to two feet, is tough as asphalt when dry but soupy mud when it gets wet. That's not prime foundation material.

So the architect decided to go deeper to ensure a sound footing. That's when he ran into tepetate, a type of brittle, light-colored volcanic rock endemic in San Miguel and other semi-arid and desert areas. Tepetate is a cousin of caliche, a hard calcium carbonate deposit found in New Mexico and other desert areas.

Blah, blah, blah. Whatever. The stuff is nasty.

Tepetate's only positive side, as far as I've been able to determine, is that a pulverized version of it can be used to pave rural roads relatively inexpensively. Just dump a few truckloads of it on the ground, spread it around sloppily with a backhoe, drive over it for a couple of months and then just wait for the rainy season. The result won't look like Rodeo Drive but it will be as tough as most road surfaces.

The only hitch is that it might wash off if you have a slope or drainage problems, but that's simple to fix. Just call one of a hundred purveyors--tepetate is as easy to find as corn tortillas--and tell them to bring a few more truckloads of the stuff and you're all set.

On the other side of San Miguel there is hardly any black topsoil, just straight tepetate the second you set foot on the ground. Digging a three-foot-deep hole to plant a fruit tree could well require a backhoe. Still, hardy souls garden and farm in this stuff, many with beautiful results.

Indeed, whenever I start to complain about our muddy black top soil at Rancho Santa Clara, my guardian angel taps me on the shoulder and goes: "Awshuddup! It could be tepetate!"

Because tepetate can be brittle--a stone-like chunk of it will crack and splinter when whacked with a sledge hammer--the architect had to dig a little deeper to find solid rock. That required extensive banging through the tepetate by a backhoe equipped with a jackhammer attachment at one end. Even the relatively new machine broke down repeatedly.

In the end we got our hole dug but it turned out to be a far more complicated and expensive project. The outside walls, made of field stones collected on site, had to be considerably wider at the bottom, I suspect to guard against any shifting. On the inside of the stone walls is another wall, about eight inches thick, of concrete reinforced with rebar.

One pleasant surprise, for San Miguel, is that the architect used concrete trucks and a snorkel to pour the concrete walls. At many, if not most, residential construction projects here the cement or concrete is mixed by hand in small mounds and then hauled in plastic five-gallon buckets to the waiting wood forms. Bucket after bucket, hundreds of them, carried on the shoulders of laborers, sometimes up to a second or third story, in a spectacle as primitive as it is slow and inefficient.

Wouldn't it be faster, and therefore cheaper, to use premixed concrete at all these sites? Faster yes, but probably not less expensive: Labor here is so cheap, and unemployment so high, that the cost of one cement truck will buy you a hundred hours of work, and you'll end up saving money.

And even if the building goes up faster using mechanized equipment, speed is not necessarily a prime concern in the San Miguel construction trades.

When we were pricing a chain-link fence to put around the property, I stopped at Ferretería Don Pedro, the local hardware emporium, and asked if we could rent a gasoline-powered post-hole digger, as an alternative to some guys digging hundreds of holes through the tepetate and rock by hand.

One of Don Pedro's young sons explained that equipment rental is not available here. And so he looked up post-hole diggers in a tool catalog of a foreign manufacturer. He seemed genuinely perplexed by my query.

"Why don't you just use a bunch of guys with picks and regular diggers?" he finally asked.

I replied, rather officiously, "Well, with a power digger the job would go much faster. Digging through all that rock will take forever, don't you think?"

Now more amused that puzzled, the guy just smiled. "I suppose, but what's the rush?"

In this case, San Miguel's logic won. Some fencing contractor put up our fence, using a crew of a dozen guys with manual diggers. I don't remember how long it took.

I'm not at all sure whether the massiveness of our cistern structure was the result of careful engineering calculations, or just a much cruder effort to overbuild everything--and then some--just to be safe. We know it has set back the construction schedule by about two weeks.

It hasn't saved us any money either. We may be down as much as US$10,000 by the time this rainwater hole is all finished.

In a way the cistern reminded me of the time Stew and I built a false ceiling at a building in Chicago. We didn't want to take any chances of it falling down on our heads and so we used enough two-by-fours to build a three-car garage. When a paunchy city building inspector looked at our handiwork, he shook his head and mumbled: "Well, one thing is for sure. This fucker ain't coming down."

And so may it be with our expensive cistern.


  1. Just as a basis of comparison, our swimming pool in Florida is 36 feet by 18 feet and holds 22,000 gallons. Now that you've had experience, how quickly does your cistern fill up during one of the gully washer San Miguel storms? A tropical storm lasting two days on the Gulf Coast adds one foot of water to our pool, but we don't divert water from our roof drainage system to the pool.

  2. Bill: I think we've figured that our water holding tank is probably like a fair-sized swimming pool. A couple or three of those San Miguel downpours and the cistern will be pretty much filled up because we have a pretty large roof area. But if you get only drizzles and light rains, then it will take longer. We haven't had any problems with water supply. Last year we got only half of the rain we're supposed to get, though the drought that hit Texas and northern Mexico didn't hit us. We'll see what happens next year.