A concrete mixer can be expensive, especially if you only plan to use it once or on occasion. Instead, you can make your own from a plastic barrel. Start off with a standard 144 litre (32 gallon) rubbish barrel for a do-it-yourself concrete mixer. Adjust the plans based on the materials that you have available or you can visit your local hardware shop.
Place the lid of the rubbish barrel on a work surface. Draw a 45 cm (18 inch) diameter circle in the centre of the lid with a compass.
Drill a 1.2 cm (1/2 inch) hole through the centre of the lid. Cut out the circle from the centre of the lid with a jigsaw. Use the 1.2 cm (1/2 inch) hole to allow the blade to access the centre of the lid to begin the cut.
Place the plywood panels on a work surface. Draw a half circle with a diameter of 65 cm (26 inches) on one 80 cm (32 inch) edge of each panel. Use the flexible ruler to achieve an even half-circle. The barrel will rest on it.
Cut out the half-circle from each plywood panel using a jigsaw.
Fasten one caster in the centre of the half-circle edge and one approximately 5 cm (2 inches) from each end on each panel. This will allow the barrel to roll while resting on the edges of the panels.
Place the panels parallel to each other with the half-circle edge facing upwards approximately 70 cm (28 inches) apart. Place one 5 x 10 x 70 cm (2 x 4 x 28 inch) board between the bottom edge on each side of the panels.
Fasten the bottom panels to the ends of the boards using 7.5 cm (3 inch) coated screws. Use two screws per joint.
Align one 5 x 10 x 70 cm (2 x 4 x 28 inch) board between the top edge of each side of the plywood panel. Fasten the boards to the panels in the same manner as the bottom boards where fastened. This will create a wooden frame for the barrel to spin on horizontally.
Insert the 5 x 10 x 60 cm (2 x 4 x 24 inch) boards into the barrel. Space them out evenly with the 5 cm (2 inch) edge against the inside of the barrel. These are the paddles of the mixer. Screw from the outside of the barrel into the edges of the paddles to fasten them in place. The bottom edge of the boards should rest on the bottom of the barrel. Space the screws every 7.5 cm (3 inches).
Place the barrel onto the frame. The barrel will sit on the casters. Snap the lid in place. To operate the mixer, spin the barrel by hand on the casters.
Apply an exterior finish to the mixer. Allow the finish to dry.
Place the mixer close to your work area prior to mixing concrete. Wash the mixer thoroughly after each use.
Wear eye protection when operating power tools.