Laying a foundation for any external structure, such as a storage shed, requires construction of a concrete pad. The pad is a combination of drainage materials, such as crushed gravel, beneath the pad, with steel rebar rods in the pad for stability. The optimal thickness of any concrete pad that will hold heavy equipment is 5 inches. A concrete form built out of 2-inch by 6-inch beams accomplishes the proper depth leaving sufficient room for the crushed gravel base.
Place the shed on the ground in the desired location. Mark the ground with the perimeter dimensions for the shed plus 3 to 4 inches with marking paint.
Dig out the area within the perimeter markings to a depth of 6 inches. Compact the ground with a hand tamper, a long pole with a flat base and two handles on the side, or a mechanical tamper available for rent from most hardware stores.
Place landscape fabric over the base of the hole. Overlap the sides of the hole slightly and any seams by 3 inches.
Place 2-by-6 beams along each edge of the hole. Stand all beams so that the 6-inch edge is vertical. Hammer 3-inch nails through the sides of beams into the ends of attached beams to create the corners. Hammer nails into the upper edge of beams at an angle into the ends of attached beams to create straight lines with multiple beams.
Drive ground stakes into the ground with a mallet spaced every 2 to 3 feet along the exterior edge of the form. The tops of the stakes must sit flush with or just below the top edge of the form.
Place a level on top of the form. Raise and lower the form until the structure is levelled side to side and front to back. Anchor the form to the ground stakes with 3-inch nails driven through the stakes into the form once the form is levelled. Leave a little bit of the nail exposed to make it easier to remove.
Pour a 1-inch layer of crushed gravel into the hole. Compact the gravel with a tamper. The depth should be 5 inches below the top of the form. Add or remove gravel to achieve the proper depth.
Mix and pour concrete into the hole until the hole is half full. Lay strips of rebar out on top of the concrete into 2-foot-square grids.
Fill the remainder of the form with concrete until the concrete is flush with the top of the form. Drag a spare wood beam slowly along the top edge of the form to remove excess concrete and to initially level the concrete surface.
Pull a float across the top of the concrete to smooth over the surface and to press any visible gravel into the cement. The surface should be smooth and free of obstructions or marks. Allow the surface water to evaporate leaving a dull-grey appearance to the concrete.
Finish the concrete surface with a trowel for a smooth finish or dragging the bristles of a push-broom over the surface for a skid-resistant finish.
Allow the concrete to cure while covered with plastic for seven days before applying sealants or paints or attaching the shed.
Tips and warnings
- Allow the concrete to cure while covered with plastic for seven days before applying sealants or paints or attaching the shed.