How to Build a Concrete Pad for an Air Conditioner

Determine the size of slab necessary for the air conditioner. This information is available in the manufacturer’s manuals. If the size is unknown, a 5-by-5-foot slab will fit most situations.

Excavate the sod from the location including a space about 6 inches around the planned sides of the air conditioner pad to allow a workspace.

Build a form out of 2-by-4 inch lumber. Cut the lumber 3 inches longer than the planned size of the air conditioner pad. Fasten the four pieces together to form a square with an interior size the same as that planned for the pad.

Place the form on the excavated opening. Drive wood stakes on the outside of the form. Place a 4-foot carpenter’s level across the form and position the form until it is level and fasten it in place to the stakes.

Calculate the amount of concrete necessary. Multiply the length times the width times the depth of the slab. If the pad is 5 feet square and 4 inches thick, for example, multiply 60 times 60 times 4 for 14,400 cubic inches of concrete. A cubic yard of concrete is 46,656 cubic inches. Our 5-foot square slab requires 0.3 cubic yards.

Pour the mixed concrete into the form and level with a screed. A screed is a straight board placed across the top of the form and drawn across the concrete to level the surface.

Trowel the concrete surface to produce a smooth finish. Work the trowel across the surface repeatedly to produce a smooth surface. Allow the concrete to dry overnight before removing the forms. Backfill the soil around edges of the pad.