Build the Mixer
Cut four triangular mixing fins out of sheet metal using tin snips -- the triangles should be nearly as long as the height of the barrel, and 6 inches wide at the base.
Bend the long, straight edge of each triangular mixing fin to a bit less than 90 degrees using the vise grip locking sheet metal tool to create a 1-inch wide mounting flange.
Position the triangular mixing fins at equal distances around the inside of the drum, with the wider base of the fin at the bottom of the drum. Notch the mounting flange if necessary to ensure that the fin fits tightly against the side of the drum. Secure the fins in place temporarily with strips of duct tape.
Drill holes through the mounting flange of the fins and through the walls of the drum -- space the holes every six inches along the length of the fins.
Secure the fins in place permanently with bolts. Place a rubber washer onto each bolt before inserting the bolt from the outside of the drum into a drilled hole in the barrel and fin flange. From the inside of the drum, add another rubber washer, a lock washer and a hex nut to the bolt and tighten securely. Hold the hex nut in place with a second wrench if necessary.
Mix cement by adding concrete mix and water to the drum, securing the lid in place, tipping the drum onto its side and rolling the drum back and forth vigorously.