Puerto Rico produces more cement in proportion to its population than any other place in the Western Hemisphere, including the United States. In the world it is second only to Belgium in annual per capita production. Why does this tiny Caribbean island manufacture almost a thousand pounds of cement per inhabitant per year? One answer is obvious to anyone who looks around the San Juan metropolitan area today: the boom in building, and the almost exclusive use of reinforced concrete. But why is Puerto Rico's construction almost exclusively concrete? It is true that no lumber is produced in quantity on the island, that imported lumber is expensive, and that it would have to be treated to resist termites. It is also true that most of the ingredients for making cement and the aggregates for concrete abound on the island. But the real answer is San Felipe- a gentle name for a calamitous hurricane which struck in 1928- and other hurricanes, notably the one in 1932. Beside the practical reasons for the extensive use of concrete in Puerto Rico, there is the esthetic aspect. Concrete lends itself to attractive finishes and color by local builders, and seems to blend into the Hispanic-Moorish architectural tradition through the use of molded arches and screens.