Starting in 2000, a program in Mexico’s Coahuila state called “Piso Firme” (Firm Floor) offered up to $150 per home in mixed concrete, delivered directly to families who used it to cover their dirt floors. Scholar Paul Gertler evaluated the impact: Kids in houses that moved from all-dirt to all-concrete floors saw parasitic infestation rates drop 78 percent; the number of children who had diarrhea in any given month dropped by half; anemia fell more than four-fifths; and scores on cognitive tests went up by more than a third. (Perhaps unsurprisingly, mothers in newly cemented houses reported less depression and greater life satisfaction.) By 2005, Piso Firme had spread to other states, and 300,000 households—about 10 percent of dirt-floor houses in Mexico—had taken part in the program.
It helps if the street outside the house gets paved, too—not so much for health reasons as for economic ones. Economists Marco Gonzalez-Navarro and Climent Quintana-Domeque found in a 2010 study that paving the street in the town of Acayucan, Mexico, added more than 50 percent to land values and caused a 31 percent rise in rental values. It also considerably increased households’ access to credit. As a result, households on paved streets were 40 percent more likely to have cars.