Concrete objects to being frozen before it is "set," but it is exceedingly accommodating about working under water. It must, of course, be carried in some way through the water to its proper place without being washed away, but this is easily done. Sometimes it is let down in great buckets closed at the top, but with a hinged bottom that will open when the bucket strikes the rock or soil where the material is to be left. Sometimes it is poured down through a tube. Sometimes it is dropped in sacks made of cloth. This cloth must be coarse, so that enough of the concrete will ooze through it to unite the bag and its contents with what is below it and make a solid mass. Sometimes even paper bags have been successfully used. The concrete, made rather dry, is poured into the bags and they are slid down a chute. The paper soon becomes soft and breaks, and lets the concrete out. Sometimes concrete blocks are moulded on land and lowered by a derrick, while a diver stands ready to see that they go into their proper places.
Concrete is used for houses, churches, factories, walls, sidewalks, steps, foundations, sewers, chimneys, piers, cellar bottoms, cisterns, tunnels, and even bridges. In the country, it is used for silos, barn floors, ice houses, bins for vegetables, box stalls for horses, doghouses, henhouses, fence posts, and drinking-troughs. It is of very great value in filling cavities in decaying trees. All the decayed wood must be cut out, and some long nails driven from within the cavity part-way toward the outside, so as to help hold the concrete. Then it is poured in and allowed to harden. If the cavity is so large that there is danger of the trunk's breaking, an iron pipe may be set in to strengthen it. If this is encased in concrete, it will not rust. A horizontal limb with a large cavity may be strengthened by bending a piece of piping and running one part of it into the limb and the other into the trunk, then filling the whole cavity with concrete. If the bark is trimmed in such a way as to slant in toward the cavity, it will sometimes grow entirely over it.
Concrete is also used for stucco work, that is, for plastering the outside of buildings. If the building to be stuccoed is of brick or stone, the only preparation needed is to clean it and wet it; then put on the plaster between one and two inches thick. A wooden house must first be covered with two thicknesses of roofing-paper, then by wire lathing. The concrete will squeeze through the lathing and set. Stucco work is nothing new, and if it is well done, it is lasting.
Concrete has been used for many purposes besides building, and the number of purposes increases rapidly. For blackboards, refrigerator linings, and railroad ties it has been found available, and for poles or posts of all sizes it has already proved itself a success. It has even been suggested as an excellent material for boats, if reinforced; and minute directions are given by one writer for making a concrete rowboat. To do this, the wooden boat to be copied is hung up just above the ground, and clay built around it, leaving a space between boat and clay as thick as the concrete boat is to be. The wooden boat is covered with paper and greased, then the concrete is poured into the space between the boat and the clay mould; and when it hardens and the wooden boat is removed, there is a boat of stone—or so the directions declare; but I think most people would prefer one of wood. However it may be with rowboats, concrete is taking an important place in the construction of battleships, a backing for armor being made of it instead of teakwood. The Arizona is built in this way.
Concrete that is carelessly made is very poor stuff, and dangerous to use, for it is not at all reliable and may give out at any time; but concrete that is made of the best materials and properly put together is an exceedingly valuable article.
IV
BRICKS, THEIR FAULTS AND THEIR VIRTUES
The simplest way to make a brick is to fill a mould with soft clay, then take it out and let it stiffen, and then put it in the sun to dry. This is the way in which the "adobe" bricks of Central America are made. They answer very well in countries where there is little rain; but one or two heavy downpours would be likely to melt a house built of such material.