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Ferrocement Water Tank, Part 2

San Lorenzo Water 1

By Ted Uram


Power to the People

When last we left Andrew Bui, an engineer with Engineers Without Borders, he was in Guatemala trying to build a ferrocement water tank for the people of San Lorenzo. But they had run into some problems…


The town of San Lorenzo is made up of about 2,000 people, many of which are children. They did not have an adequate water supply. Bui, along with several other volunteers with Engineers Without Borders, journeyed down to see if they could help.

They worked with the mayor of the town to locate a spot to dig a well. Bui helped the mayor apply for a federal grant in Guatemala to fund the effort. Once the well was dug, a ferrocement water tanks was to be constructed. This did not happen. The town’s only generator was simply insufficient. It could not power up a strong enough compressor to blow the mortar needed to coat the wire-mesh exo-structure of the tank. To make matters worse, there simply was not a strong enough compressor around. Andrew and his crew were forced to leave.

Water storage tanks had been tried in this area before. In fact, two reinforced concrete tanks were built. One leaked like a sieve, and the other required constant repair. A ferrocement water tank would be much sturdier and could even withstand seismic activity.

A hero returns

On his first trip, Bui brought 18 students and three professionals with him. They were able to construct the entire armature for the ferrocement tank, but when they ran into the difficulties with the generator and air compressor, they realized a diesel-powered compressor was the only way to go. At one point, they actually considered  hand troweling the entire project, but the team decided to focus on making the best armature possible.

“I didn’t want to just finish quickly,” Bui stated. “I wanted it to be done right.”

Bui searched high and low, but he could not locate a big enough, diesel-powered generator in Guatemala. The closest one he could find was in Panama. Down but not out, he returned to the states.

Once in Miami, Bui went to work. He located a diesel-powered compressor strong enough to finish the job at a local Grainger dealer and had it shipped to Guatemala, all on his own dime.

Back in San Lorenzo, Bui hired eight local workers to help him spray the tank. For a test run, Bui and his crew actually coated a small test tank, only 4’ X 4’, by hand. It was miserable work.

“We had a very hard time getting the mortar to stick,” Bui said. “Plus we were working with people who had never done any kind of concrete work before. What if their arms got tired and they didn’t push the mortar all the way into the wire mesh? Are there going to be gaps where people are working so closely together?”

“If we had to do this by hand it would have taken at least five- to ten-times as longer,” Bui said. “The Mortar Sprayer was a Godsend.”

By using the mortar sprayer, one person could spray while several stood back to see where the person spraying was light, or had maybe missed a spot. It was simply much more efficient. Bui always knew he was spraying at exactly 90 psi and that he was getting even coverage.

Using the Mortar Sprayer, they finished the 26’ X 8’ tank in just four days.

There was some finishing work to be done, but Bui had a prior obligation. Before leaving, however, he trained the workers on how to finish the tank. They got to work right away.

The Basic Steps

Step 1: The floor of the ferrocement tank was lined with rebar and steel mesh. Using the Mortar Sprayer, they lined the floor and made their way up into the walls.

Step 2: The armature was sprayed from the inside out. The inside was sprayed with two layers of a ferrocement mixed with lime. “We used the lime to keep the cement from dropping off the first layer when it is sprayed to the cage,” Bui said. “Adding lime helps with that.”

Step 3: The outside of the tank was then sprayed.

All was well. In just a few days, the town of San Lorenzo now had a ferrocement water tank rated to withstand seismic activity and last 50+ years.

In the end, Bui was very glad it worked out. He nearly became a permanent resident of San Lorenzo.

“I told all my friends that I would not return to the States until this was all done.” He chuckles. “When we got that generator working and the Mortar Sprayer running, it was a huge sigh of relief on my part.”

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