The Process of Cast-in-Place Concrete Walls

Molds

• The wet concrete must be poured into molds, often called temporary forms. The concrete company hired for the project builds, according to builder's specifications, the appropriate molds out of aluminum, wood or steel. Metals are becoming more common because they can be used almost indefinitely. The concrete is then compressed and left to dry. Once the mold is cast away, a concrete block or part to a home is completed and custom built for the project. One financial advantage of this method is that there is almost no waste. Since the molds are already built to specifications, it is only the concrete that will fill the mold that is used. The trimming or smashing of wasted or unused concrete here is minimal.

Cement

• The cement is mixed at the factory. This is done so the perfect level of elements and chemicals can be added under controlled conditions. The basic, average concrete used in the CIP is 10 percent concrete, which is a sand and water paste; about 70 percent aggregate materials such as ash, rubble or silica filler; and water. The general measure of quality is the ratio of sand to water. The less water, the higher the quality of the concrete. This is largely because water in concrete freezes in winter, thereby damaging the material over many freeze-thaw cycles.

Consolidation

• One of the most important elements of the CIP process of “consolidation.” This is the process of removing air from the concrete. While there is very expensive self-consolidating concrete, the basic process is to place the wet concrete on a table that vibrates, thereby forcing any air pockets or bubbles out of the material before the concrete is poured. It is possible that builders, seeking to save money and time, will pour the concrete directly from the truck to the mold, but this will result in a lower quality product.

Additives

• Most state building codes require both insulation and a steel “cage” that supports the walls, especially in foundations. This refers to a set of either vertical or horizontal steel bars that add extra support to the concrete. It is cheaper than actually pouring more concrete to make a thicker layer. Insulation and the steel cage are built within the mold itself. The concrete is poured around it. This makes building sturdy foundations far easier than in the past and far more efficient than the hand laying of concrete cinder-blocks.