How to Pour Cement for a Patio Extension

If you have outgrown your cement or paved patio, a patio extension can be created by pouring concrete around the existing patio. Determine how much larger to make the patio before starting by placing furniture in approximate locations, inspecting the area around the existing patio for regular use such as disturbed flower beds or worn down grass or mud spots around the perimeter of the patio. Use this information and add a few more inches so you can be sure the patio extension will meet your needs for years to come.

Things You'll Need

• Tape measure
• Landscaping spray paint
• Contractor’s string
• Stakes
• Hammer
• Shovel
• Rake
• Plate compactor
• Level
• Crushed stone
• 4-by-1 lumber
• Saw
• Drill
• Screwdriver bit for drill
• Concrete
• Concrete float
• Edging trowel

Instructions

1. Use a tape measure to measure the planned patio extension area. Insert stakes at each corner by pounding the stake into the ground with a hammer. Tie a string between each stake close to the ground. Use landscaping spray paint to paint directly over the string to mark the location for the outside edge of the patio extension. Remove the string.

2. Place a level on the soil and dig a level area 8 inches below the top of the existing cement patio for the entire planned extension area. Do not dig any deeper than necessary to avoid disturbing solid soil. Rake the top of the soil to fill shallow areas and lower high areas.

3. Use a plate compactor to compact the soil. It's important to have a solid, well-packed foundation for the patio extension. The weight of the cement used for the extension will settle and pull away from the existing patio if the soil beneath the extension is not compacted well. Repeat covering the entire area with the plate compactor at least five slow passes over the entire soil surface.

4. Pour 2 inches of crushed stone into the area for the patio extension. Compact the crushed stone with the plate compactor. Pour another 2 inches of crushed stone and compact with the plate compactor.

5. Attach stakes, using a drill and screws, to the 1-by-4 lumber so the stakes are below one edge of the lumber. Install the pieces in the location planned for the patio extension by pounding the staked into the ground. Use a level to ensure that the top edge of each piece of lumber is level with the existing patio. Create slope for the extension by lowering the lumber approximately 1/8 inch per foot lower than the existing patio to ensure that water will run off the extension.

6. Wet the edge of the existing patio with water so the new concrete will not dry out too quickly. If the existing concrete is dry, it will pull moisture from the new concrete and create a gap between the existing cement and the extension.

7. Mix concrete in a wheelbarrow according to package directions and pour into the formed extension area. Fill the form all the way to the top. Level the concrete by placing a board across the existing patio and the top of the 1-by-4 lumber form walls. Pull the board slowly to remove excess concrete and fill shallow areas with additional concrete until the entire surface of the patio extension area is level and smooth.

8. Use a concrete float to smooth the top of the concrete and blend it into the existing patio. When the concrete has set up enough to hold a shape, place the lower side of an edging tool between the concrete and the boards to round the corners of the concrete.

Tips & Warnings

• Wear safety glasses or goggles while working with the plate compactor to prevent stone chips and dust from getting into eyes.

References

• Concrete Network: Make Sure the Subgrade is Compacted
• Mother Earth News: Pouring Concrete