Adding a concrete garden bench to your landscaping is a simple way to create outdoor seating on your property without much expense. While basic units of concrete benches are available at most garden centers, you can make seats on your own with cinder blocks and concrete, and they will last for decades. While this do-it-yourself project isn't difficult, allow at least a week to finish it because the concrete needs to dry.
Set two 3-foot long, 2-by-4-inch wood boards parallel to each other on a flat surface. Lay each board on one of its 2-inch wide sides, and space them 21 inches apart.
Place two 2-foot long, 2-by-4-inch wood boards perpendicular to the 3-foot long boards to form a rectangle. Set each 2-foot long board on one of its 2-inch wide sides. Make all the boards' corners flush, and secure them together with a 2-inch long wood screw at each corner.
Place the rectangular frame on a level surface. Lay one 21-by-36-inch sheet of tar paper or roofing paper inside the frame so it covers the bottom of the rectangle.
Lay pieces of broken tile, marbles, pebbles or other items made of natural material face down on the tar paper or roofing paper. Arrange the items randomly or in a pattern until you are satisfied with the layout. Lift each item one at a time, apply a drop of glue to the spot on the paper where the item was located and return the item to that location.
Coat the inside surface of the wood boards with mold release agent by using a paintbrush.
Put on a dust mask. Prepare bagged concrete mix in an old wheelbarrow by slowly adding water until the material is batterlike in consistency. Wear the dust mask until you finish with the powdery concrete mix.
Scoop the concrete into the rectangular frame to cover the paper and other items. Use an old shovel for that task. Add about a 2-inch depth of concrete to the frame's interior.
Lay two 30-inch long pieces of rebar parallel to each other and spaced evenly apart in the concrete. Fill the rest of the frame's interior with concrete. Leave the frame in place for two to three days to allow the concrete to set.
Remove the wood screws from the frame's corners, and pull each piece of wood straight outward from the concrete. Spread a tarp beside the concrete, and gently turn the concrete over and onto the tarp. The concrete will be the bench top. Peel the tar paper or roofing paper away from the top of the concrete. Let the bench top cure for two to three days.
Stack two cinder blocks on top of one another with their holes facing upward. Make a second stack of two cinder blocks 1 foot from the first stack. Ensure that the cinder blocks' tops are level with each other. Move the concrete bench top on the cinder block stacks, and center the bench top over the blocks so that about 6 inches overhang the sides.