Building A Curved Concrete Patio: A Step-By-Step Guide

Building a curved concrete patio is a great way to enhance your outdoor living space and can be a fun DIY project. It requires careful planning and preparation, as well as some specialised tools and materials. In this article, we will cover everything you need to know about how to build a curved concrete patio, from designing your patio to the step-by-step process of construction, so you can create a beautiful and functional outdoor space to enjoy for years to come.

Excavate and prepare the site

Excavating and preparing the site for your curved concrete patio is a crucial step in the construction process. Here's a detailed guide to help you through it:

Mark the Area

Use batterboards and a mason's line to lay out the boundaries of your patio. This will help you visualise the space and ensure straight lines and accurate dimensions.

Remove the Sod and Excavate

Using a sod cutter, remove the sod or turf from the marked area. Then, dig out the soil to a depth of 8 inches (20 cm). This depth accommodates 4 inches (10 cm) for the concrete slab and an additional 4 inches (10 cm) for gravel and mortar, if needed. Remember to call 811 before digging to ensure there are no underground utility lines in your work area.

Compact the Soil

Once you've excavated, it's important to compact the exposed soil. You can rent a plate compactor to uniformly pack the entire base, including the sides near the forms. This step provides a stable base for your patio and prevents future settling or shifting.

Install Layout Stakes

Drive stakes along the layout lines to provide a reference for the next steps. Place the stakes at the corners of the patio and every 2 feet (60 cm) in between. Make sure the stakes are driven straight up and down, firmly embedded in the ground. You can trim them to the correct height later.

Create a Slope (if necessary)

Check your local building codes for the required slope rate. Typically, the patio must slope away from any nearby structures, such as your house, at a rate of 1/8 to 1/4 inch (0.3 to 0.6 cm) per foot. Use a chalk line to mark the stakes at the finished height of the patio, snapping the line to transfer the marks to the rest of the stakes.

Prepare for Drainage

Consider the drainage in your yard. If water tends to collect in certain spots, you may need to adjust the depth of your excavation in those areas to ensure proper drainage. It's essential to prevent water from pooling on your patio.

Spread Gravel

Spread gravel on the compacted surface in 2-inch (5 cm) layers. Compact each layer and continue adding gravel until you have a bed that is approximately 4 inches (10 cm) deep. The gravel base is crucial, especially in areas with poor drainage or freezing temperatures. It provides a stable and well-drained foundation for your concrete patio.

Level the Gravel

Use a homemade template that extends down from the tops of the forms to check the thickness of the gravel. When the template just touches the top of the gravel, you'll know it's thick enough. Ensure the gravel extends slightly under the edges of the forms to provide a solid base for the concrete.

Build forms and set up stakes

Building a curved concrete patio requires careful planning and preparation. Here is a step-by-step guide to building the forms and setting up the stakes:

To build the forms and set up the stakes for your curved concrete patio, start by marking the ground with marking paint to indicate the desired shape of your patio. Use 12-inch (30.5 cm) hardboard siding ripped down to 6-inch (15 cm) strips in 16-foot (4.8-meter) lengths. Flex this material to the desired shape, staking it down as you go. Remove the sod and dig out the path for your patio, ensuring you dig out about 3 inches (7.6 cm) wider on both sides of the paint marks to allow for the forms. The depth of your excavation should be 6 inches (15 cm), including the thickness of the concrete slab and the gravel base.

Next, pound in stakes about 1 foot (30.5 cm) from the ends of the form positions. Screw the forms to the inside of the stakes using 1-1/4 inch (2.5 cm - 3.5 cm) drywall screws. Ensure the tops of the forms are about 1 inch (2.5 cm) above the cut grass height to allow for easy mowing and a neat appearance.

Now, space and level the opposite form sides using a homemade gauge board. This can be a 1x4 piece of wood that's a few inches longer than the width of your desired patio. Screw short blocks onto the bottom of the gauge board, spaced according to the width of the patio. Use this gauge board to position the forms and stakes, ensuring a consistent width along the entire length. Rest a 4-foot (1.22-meter) level on the gauge board to keep the forms level.

Finally, pack the underlying soil with a plate compactor to uniformly compact the base, including the sides near the forms. This will create a stable base for your concrete patio.

Pour concrete into forms

Now that you have your forms in place, it's time to start pouring the concrete. If you're using a wheelbarrow, it's a good idea to build a temporary ramp over the forms so that you don't accidentally knock them out of place when you're pouring the concrete. Start by pouring the concrete into one corner and then work your way along, dumping loads of concrete against each other. Use a shovel to spread the concrete into the corners and against the forms and expansion joints. If you have a helper, they can do this while you continue to pour.

If you need to reach the interior of the pour, lay a wide board across the forms so you can access the middle of the patio. If the concrete causes the wire mesh to sink, use a rake to pull it back up so that it sits in the middle of the slab.

Use a shovel or rake to work the concrete up and down, removing any air pockets, especially alongside the forms. It's important not to overwork the concrete at this stage, as this can force the heavy aggregate to the bottom of the slab and bring up small particles that can cause defects in the finished patio. Instead, space out your placement along the form, placing each batch against the previous batch to fill the form.

Once you've poured the concrete, it's time to start flattening the surface. With a helper, pull a screed (a long, straight 2x4) across the forms to level the concrete. Tilt the screed forward and slide it from side to side as you push it forward. Shovel off any excess concrete in front of the screed or fill in any low spots. Make a second pass with the screed tilted in the opposite direction.

Next, you'll want to use a bull float to smooth and compact the concrete. Work the concrete until water forms on the surface. For small surfaces, you can use a darby instead of a bull float.

Smooth and level the concrete

Once you've laid out the concrete, it's time to smooth and level it.

Start by using a strikeoff (a straight piece of wood) to level the concrete. For larger projects, do this in batches rather than waiting until all the concrete is placed. Move the board slowly, using a side-to-side sawing motion, and make two passes. For narrow forms, two people will make the work faster and more efficient. If necessary, a third person can shovel extra concrete into any corners to save time.

After striking off, use a darby or bull float for the initial finishing. This will smooth down high spots and fill small hollows. Move the darby in overlapping arcs, then repeat with overlapping straight, side-to-side strokes. Keep the tool flat and don't let it dig in. For larger jobs, use a bull float. Push it away from you with its leading edge raised slightly, then pull it back almost flat, overlapping your passes.

Next, run a mason's trowel between the concrete and the outer edges of the slab form. Follow this with an edger. Run it back and forth to smooth and compact the concrete. Unless the tool has a toboggan end, raise the leading edge slightly as you move it.

Large slabs of concrete will crack, so to control the cracks, set joints with a 1" deep jointer and a straight guide board to make control joints. Kneel on a board to reach the middle of a wide slab. The depth of the control joints should be a quarter of the slab's thickness. Make marks with a pencil for any edging or jointing, which can be removed later by floating.

Now it's time to float the concrete. After the water sheen has disappeared but before the surface has become stiff, use a wood float or a magnesium hand float. The latter gives a smoother surface. Hold the tool flat on the surface and, if necessary, kneel on boards to reach the middle of a large slab, then finish over the board marks as you work backwards.

Let the concrete cure

Now that your concrete patio is in place, it's time to let it cure properly. This process is crucial to ensure the strength and durability of your new patio. Here are the steps you should follow:

• Keep the concrete moist: Concrete needs to be kept moist during the curing process to prevent water from evaporating too quickly. This can be done by spraying it with water frequently—about five to ten times per day for the first seven days. This technique is called "moist curing" and results in stronger concrete.
• Cover the concrete: If you can't frequently spray the concrete with water, you can cover it with polyethylene sheeting that's at least 4mm thick or a concrete curing insulating blanket. Wet the concrete first, then cover it, and weigh down the covering with bricks or rocks. Repeat this process daily for seven days, rewetting and recovering the concrete each time.
• Pond curing: Another option is pond curing, where you create temporary berms around the concrete slab and flood the area with one foot of water. This method is more commonly used for large-scale projects, as it requires a significant amount of soil to form the berms.
• Apply a curing compound: If the above methods are not feasible, you can use a curing compound. These compounds are available at DIY stores and ready-mix concrete companies. They form a protective film when sprayed onto the concrete, preventing water from evaporating and allowing it to cure evenly.
• Avoid foot traffic: It's important to keep people and pets off the concrete for at least 24 hours. Even after this initial period, it's best to avoid walking on it for at least 3–4 days.
• Avoid vehicle traffic: Similarly, do not drive a vehicle on the concrete for at least 10 days. After this period, regular passenger cars can drive on it, but heavier vehicles like pickups or RVs should be kept off until the concrete reaches its full strength, typically around 28 days.
• Avoid painting or staining: Resist the urge to paint or stain your concrete too early. Wait for at least 28 days to allow the concrete to fully harden and for the hydration process to be completed.

Frequently asked questions