Low temperatures will delay or prevent proper setting of the grout. Once the temperature of a structural member has dropped below 40 degrees F, attempts to maintain the temperature of the grout at a higher level will fail due to the large ratio of the bulk of the member to that of the ducts. When grouting in cold weather, protection of the structural member should be provided by a heated enclosure. Temperature of members at the time of grouting must be above 50 degrees F and should be maintained at this temperature for at least 48 to 72 hours of until job cured cubes reach a minimum compressive strength of 800 psi. Injection should be carried out in a manner which ensures the expulsion of air from the duct by the grout. Therefore, when grouting vertical or nearly vertical ducts, it is essential to inject from the lowest point of the duct. The rate varies widely from job to job according to the mixture to be used, the length, number and size of the tendons, the size of the ducts and the orientation of the tendons within the ducts. Although pressure by itself is of limited value as an indicator it is the only means of determining whether the proper injection rate is being used. An excessively high pressure will indicate too high a rate of injection and may cause water to separate by being pushed out of and ahead of the remaining grout ingredients. This separation results in blockage of the duct passage. Therefore, the pump must have a variable rate of displacement. The rate should also be uniformly adjustable during the pumping operation. Unbonded tendons must be permanently protected applied coating of galvanizing, cadmium plating, epoxy, grease, wax, plastic, bituminous or other suitable material. Tendons for unbonded work are usually coated by the manufacturer with a wax designed primarily to give protection during transportation and storage on site and also to assist in lubricating the tendon during tensioning. During manufacture, the tendon is also coated with a grease, primarily to provide additional lubrication for the tendon but also to provide corrosion protection for the tendon up to the time it is stressed. Rust inhibitors are usually added to the grease together with additional compounds to ensure its uniform consistency in extremes of temperature.