If you like to garden and have a nice property, a garden shed is a useful and valuable addition that improves the look of your home and adds value at the same time. Contractors can demand very large markups for their labour, however, which can double or even triple the actual cost of pouring a concrete slab and of a modular shed unit. If you have a few free nice summer days, you can easily form and pour a foundation yourself in preparation for a gardening shed.
Choose the area where you wish to assemble your shed, and prepare it by removing debris, grass, and other plants and ensuring that the land is fairly level.
Construct a perfectly square 1.8 x 1.8 m (6 x 6 foot) frame out of 5 x 10 cm (2 x 4 inch) boards. Measure 30 cm (1 foot) in from each end of the longer boards, and mark these positions with a pencil. Line up the short edge of each 1.8 m (6 foot) board with one of the pencil marks on one of the 8-foot boards, and nail them into place. Place the remaining 2.4 m (8 foot) board against the unattached ends of the shorter boards, ensuring that each of the edges of the smaller boards are one foot in from each end of longer board, and nail this board into place as well.
Hammer 12, 5 x 5 cm (2 x 2 inch) wooden pegs around the frame, 3 against each side, approximately 60 cm (2 feet) apart. Saw off the tops of all of the pegs with a hacksaw so that they are even with the frame. These will hold the frame in place as you pour your concrete.
Use a shovel to dig a 10 cm (4 inch) deep tunnel approximately the width of your spade around the interior perimeter of your frame so that the edges of your foundation are weightier and to give it strength. With a garden hose, spray the bare soil within the frame, and tamp it down tightly with a long-handled, hand-held tamp until the surface is flat and level.
Move the concrete from the packaging into buckets or a wheelbarrow so that you can easily transport it. Carry or push the concrete to the pour frame, and fill the frame with a layer of concrete that covers the entire bottom of the frame and is 2.5 cm (1 inch) thick when it settles. Smooth the cement with the shovel. Drop a 1.5 m (5 foot) piece of reinforcing rod in the approximate centre of the wet cement, and wrap a piece of #3 rebar around the inside of the frame approximately 5 cm (2 inches) from each side. Do not cut the rebar, but bend it carefully at each corner. Secure the rebar and reinforcing rod together with tie wire where they intersect.
Fill the rest of the frame with concrete. Tap the outside of the pour frame with a hammer to eliminate air bubbles and settle the concrete. Tap each side 3 to 4 times.
See-saw a levelling screed back and forth along the top of the concrete pour frame to level the surface of the concrete. Smooth the surface of the concrete slab with a handheld rubber float, using wide, sweeping fan motions. Allow the concrete to cure for 30 minutes, and smooth the surface again. Wait another 30 minutes, and float the surface one final time. Allow the concrete slab to rest for 2 to 3 hours so that the surface moisture evaporates.
Use a smooth metal trowel to finish the dried surface of the concrete until you are satisfied with the appearance. Allow the concrete slab to cure for at least two days. Lightly spray the slab daily with a garden hose so that it continues to cure levelly. Once the slab has completely cured, remove the frame. You may have to disassemble it from around the slab.
When buying supplies, examine the selection of concrete available and choose the product that is right for your area. Read the packaging of the product you choose since this will tell you how much area one measure of the concrete fills, which varies from product to product. Buy enough concrete to form a standard 1.8 m x 1.8 m x 10 cm (6 foot x 6 foot x 4 inch) slab and have the product mixed in the shop, which is a standard practice. Dress appropriately to pour the concrete. Cover your arms, legs, and feet completely. Wear safety goggles and protective gloves.