Perlite insulating concrete consists of an appropriate mixture of portland cement, perlite aggregate and water. Its weight can be varied in the range of 20 to 50 pounds per cubic foot, depending on the mix design selected. This is in comparison to sand and gravel concrete which weighs 140 to 150 pounds per cubic foot and the 60 to 120 pounds per cubic foot weight of expanded slag, shale or clay. Because of its exceptionally light weight, perlite concrete is not considered a true structural concrete. However, it is the strongest concrete in its weight class and has more than adequate strength for floor fills, light structural roof decks place over form boards, and metal lath or paper backed wire mesh, and makes an economical and versatile insulation fill over metal decking and structural concrete. It can also be sprayed as a fire retardant backup for metal curtain walls. The step by step transit mix operation is as follows. (1) Determine the load of the mixer. (2) Add to the mixer the correct amount of water for the load. (3) Add the correct amount of air entraining agent and cement to the mixer and mix until a slurry is formed. (4) Add the required number of bags of perlite aggregate. (5) If the drum is rotated during transit, it should be at slow speed for no longer than 5 minutes. (6) Upon arriving at the job site, mix at top speed for at least 5 minutes and not more than 10 minutes. (7) Discharge in normal manner after checking the wet density for conformance to specification range. (8) Rotate the drum at idle speed when discharging last of load to insure complete discharge of concrete. (9) Do not wash out drum between loads.