Q.: We are consulting on a freezer floor job. The floor is to be 6 1/2 inches thick, with welded wire fabric, placed on a 6-inch layer of polystyrene over a vapor barrier on a sand base. The floor is large enough to require a column line down the middle, so the floor contractor plans to use a bulkhead and key joint along the centerline. The architect-engineer does not want the concrete floor contractor to use any stakes for the forms. How can the contractor achieve adequate flatness (the new designation of F 35 is specified) without having well-anchored, stable forms at the center?

A.: Some contractors are able to achieve this degree of flatness while using wet screeds (piles of fresh concrete set to predetermined levels), but if anyone tries to use wet screeds in an application like yours they will have to devise some other way than stakes to establish the levels of the tops of the wet screeds.

A good solution is to use screed rails, a new development described in the article "Precast Leave-in-Place Screed Rails for Floor Construction," CONCRETE CONSTRUCTION, May 1984, page 483. The rails are made of reinforced concrete and serve as guides for screeding. Their design provides for interlocking of adjacent strips of floor slab and for use of tie bars across the joint if desired. Rails are set on pads of concrete and leveled with a surveyor's transit. Experience seems to show that they can be installed faster than ordinary floor forms and that they are stable during floor construction operations.

Two manufacturers known to us are: Permaban Inc., 1318 East State Street, Rockford, Illinois 61108; and Alimak Inc., 1100 Boston Avenue, Bridgeport, Connecticut 06610.