Formwork is a total system of support for cast concrete. The system should include forms, ties, and hardware, supporting members and bracing. Of decreasing use today, the job-built form is being replaced by patented systems. It consists of four by eight foot sheets of plywood and two by four inch studs. Ties are run through holes drilled in the plywood and secured to walers, usually double two by fours running horizontally on two foot centers behind the studs. Ties are normally referred to as washer ties but are also called snap ties. On heavy construction, she-bolts and coil ties may be used. The main advantages for the job-built form are low initial cost of materials, workmen's familiarity with it, and the occasional possibility of using the same materials elsewhere in construction. However, reuse of formwork is very low and usually it is scrapped. Prefab systems are usually a combination of steel and plywood or all steel. They offer three distinct advantages: (1) the possibility of assembling components for almost any size or shape of form; (2) the need for little on-site skilled labor; (3) the possibility of reusing the same forms one time as part of a large section and another time as individual units. The first step in evaluating a formwork system is to look at the requirements of the finished concrete. With this information the different methods or systems can be explored that will produce a satisfactory job at the lowest possible cost. One must also pay special attention to versatility. Almost all prefabricated systems are designed for most types of construction, allowing contractors to bid a variety of jobs. Things to consider are whether the forms can be set in combination- vertically and horizontally- and whether they can be removed and replaced at any point for casting pockets. Maintenance operations must be also be kept in mind.