Formwork and the way it is used and handled affects the quality of the concrete and the concrete finish. Some of the bad effects that forms can potentially have on the surface are obvious- bad form joints, offsets or poor facing material- but others are no so commonly understood or appreciated. Not all differences in concrete surface appearance that are sometimes attributed to the forms, however, are actually caused by them. They may be caused by differences in concrete workability, the use of admixtures, concreting temperature or concreting practices. Freshly placed concrete exerts hydrostatic pressure laterally on the forms. This pressure is not affected by the length and width of the formwork but only the height of the concrete placed. The pressure at a given depth is the same in all directions and acts perpendicularly to the surfaces that are containing the fresh concrete. Pressure increases with the forms as the height of fresh concrete increases except that when the concrete sets it ceases to transmit further pressure from above. Forms may have deflected or bulged at a given level because of concrete pressure. When the concrete at this level hardens the forms will not bulge further but neither can they return to plane. The effects of impact during placing can vary depending upon the height of the forms or the height of the drop. The faster the rate of placement the greater is the impact pressure likely to be. The height of drop of fresh concrete can be reduced by the use of elephant trunks or tremies. Another method is to erect forms and place simultaneously. One side is usually formed to its total height while the second or opposing side is initially built only to the height of the first lift. As the placing strarts the next lift of forms is erected and the placing operation follows close behind. The method not only avoid long drops but also makes placing and vibrating easier and keeps all crews busy. Other factors are vibration, form joints, horizontal construction joints, vertical construction joints, release agents, form materials, and form removal and finishing.