The second method, that of applying a “dry” finish, is to avoid touching the surface to be finished until after the slipping operation is completed full height. When complete and the form has been removed, the walls are float-finished from a swinging stage by applying either a sand finish or a cement-plaster finish. If this method of finish is to be used, (the finisher’s scaffold) is usually omitted except at critical areas where it is, or may be necessary lo have access under the form. Thus, the cost of fabricating and installing a finisher’s platform is saved and can be applied to (he higher unit cost of applying the finish in this manner. If a smooth finish is desired on the exterior of the building, a piaster skim coal can be applied over the rubber-float finish. Sandblasting of slip-formed concrete is not recommended. The possibilities of uniform texture are practically nil. Furthermore, if sandblasting is attempted and found unacceptable, corrective procedures are costly in both time and money.
A basic consideration in setting up a slip-form is the type of concrete finish that is going to be required. The normal “slip-form finish” is a rubber-float finish that is applied to the wet surface of the concrete as the slip progresses or applied dry after the slip is complete, In the first method, a finisher’s platform is suspended below the form and the finishing crew works with the freshly exposed concrete to give it the texture required. A membrane cure is sprayed on the surface after the finishing operation is complete, and it is usually unnecessary to go over the surface again once the slip is complete. The finisher’s platform can be seen below the form.