For shaping concrete to a form required, the usual practice is to make a form of planks or timbers, well braced, enclosing the space which the concrete is to occupy. The mixture is carefully made in a mixing machine or by men with shovels, wet with clean water to a mushy consistency, deposited and tamped in place. Sea water has not an adverse effect on Portland cement of good quality. When once wet, the mixture must be promptly placed in the form, as it will "set" in an hour or less. After setting, the mass is at first very weak and may be crumbled by pressure of the hand, but if left undisturbed it gradually hardens to the consistency of stone, requiring months or years for reaching final limit of hardness. In setting and for a few hours afterward, the mixture must be kept wet. In extensive work, where a form cannot be filled in one day, the upper surface is left rough at the end of each day's work to give a suitable surface for the close bonding of the mixture deposited the following day.

When concrete is dumped into a form submerged in water, it is essential that the mixture be subjected to as little wash as possible for the fine particles of the different materials composing the cement must be thoroughly mixed, and these must form unbroken contact throughout the interstices of the sand and stone in order to insure a solid, well bonded mass after setting.

Concrete work is practically impervious to water, but not absolutely so in all cases.