How to Build a Concrete Form for a Patio

Build frames to control the shape of drying concrete.

Extend the life of your concrete patio by taking the time to build a form before you pour the wet concrete. Building a concrete form after excavating and before laying a course of gravel will also ensure your patio slab has crisp corners and does not spill onto surrounding ground. Leveled edges of the form also help when leveling the slab while pouring the concrete.

Things You'll Need

• Wooden stakes
• String
• 2-by-4 boards
• Table saw
• 4-inch wood nails
• Hammer
• Carpenter's square
• Level

Instructions

1. Drive wooden stakes into the ground around the perimeter of the excavated area at intervals of approximately 4 feet. Do not set stakes directly into the corners of the excavation site, and use a length of string to keep the stakes in a straight line against the edge of the excavated area.

2. Set a 2-by-4 board into place against the wooden stakes. Cut the board down to size, if necessary, with a table saw. Set the end of the board into a 90-degree corner of the patio slab. Hold the slab up to leave a 2-inch gap below, and drive nails through the wooden stakes and into the 2-by-4 board. Use nails measuring 4 inches long, and leave an inch sticking out to make removal and deconstruction of the form easier.

3. Butt a second 2-by-4 against the cornered end of the previous board, along the adjacent edge of the patio and against the row of wooden stakes on this side. Ensure the corner measures exactly 90-degrees and adjust as necessary with a carpenter's square. Level the top edges of the two adjacent boards and drive two nails through the side of the first board into the end of the second board. Reposition the wooden stakes as necessary to set against the edge of the board and drive nails through the stakes and into the second board, leaving an inch of the nail head sticking out. Repeat this process for all corners you encounter.

4. Add additional boards when one standard, 8-foot-long 2-by-4 does not extend across the full length or width of the patio. To add an extra board, measure the length required and cut the board to size, and then set the board into place, holding it 2 inches up from the surface below. Ensure the top edge of this added board is flush with the top edge of the adjacent board. Drive nails through the wooden stakes and into the added boards. Set extra wooden stakes into place at the ends of boards you must butt together along the sides of the patio perimeter, and drive nails through these stakes and into the boards.

Tips & Warnings

• Place a thin plastic form against a home when pouring a patio that connects with the side of the home. This form cannot be removed later.

• Apply, level and compact a 2-inch layer of gravel below the frame and pour the concrete slab patio to measure at least 4 inches thick.

• Always wear eye protection and high rubber boots when working in or around concrete. Concrete companies add fiberglass and other additives to make it stronger. These additives can cause irritation to skin and eyes if they come into contact with them.

References

• Berkshire Eagle: Step-By-Step to a Concrete Patio

Resources

• Ask the Builder; A Patio of Concrete -- The Right Way; Tim Carter