If suitable fill material is readily available at the site, an earth form may not only prove cheaper than any other method of forming but should also ensure greater contour accuracy, both initially and under load. The economies of earth forming are basically dependent of the overall design of the structure and the availability of suitable material for creating the form. Obviously, the haulage and removal of large quantities of fill to and from a site could rapidly become far more expensive than even the most complicated formwork. Haulage distances will usually be the deciding influence in this matter, although it must be remembered that material can often simply be rented for a job, formed and then hauled away again after the job is complete. For most jobs, this availability problem will usually be settled by the nature of the site itself. The structural design, on the other hand, can often be effectively adapted to exploit the advantages of earth forming. In other words, to obtain the maximum benefit from the method, consideration should be given to the use of earth forms as early as possible in the design and planning of the project. From the structural viewpoint, the earth forming technique will then lend itself basically to any of three main design and construction approaches: site-precasting; casting in place; or lift-slab procedure. Site-precasting in earth forms is largely restricted to segmental construction, in which the structure can be conveniently erected as a series of pie-shaped, arched or other elements that may or may not be identical. This approach usually involves the least earth moving and casting can proceed in stacks. If sections are precast on top of the other, a good release agent must be used to break the bond between sections. Conventional form coating are less satisfactory in this respect, and it is best to select a proprietary combination bondbreaker and curing agent specially formulated for this purpose. This must be very carefully and throughly applied to the surface according to the manufacturer's instructions. Precast design must also be based on accommodation the extra stresses involved during the lifting and erection process. Direct casting in place requires the contractor to both shape and level in one operation and this involves the complex use of surveyor's instruments. If concrete is to be cast in its final position, it naturally will involve the greatest amount of earth handling. With the lift-slab method it is necessary to cast the foundations first and then to erect the supporting columns around which the jacking, with all jacks controlled from a central console, is essential to structural shapes of regular contour.