The best way to pour a curved concrete edge around a large, grassy area is to use a curb machine. You can rent these machines from a commercial equipment rental company. They aren't hard to operate and allow you to create professional borders and curbs to mark off flower beds, stepped landscape features and pathways. The curb machine uses templates to make different curb shapes for whatever kind of border you want.
- Skill level:
Things you need
- Portland cement
- 3 227g. bags of sand, 1 bag for every bag of cement
- 2-man curb machine
- Wheelbarrow or small concrete mixer
- Garden hose
- Bundle of wooden stakes
- 100-foot roll of string
- Roll of curb-reinforcing wire
- Concrete trowel
Mark the path of the concrete border you are installing with wooden stakes. Run string along the stakes to provide a guide for the curb machine. Dig a trench the shape and size of the border you plan to lay down, using a shovel. A standard curb requires a 2-inch-deep by 9-inch-wide trench. Other shapes will vary, though the width of the trench is usually 9 inches. Pull up the stakes and string and clear the dirt away from the trench for 1 1/2 feet on both sides so the curb machine has room to roll on level ground.
Mix a 5-gallon bucket of cement with 3 1/2 buckets of sand in the mixer or wheelbarrow. You'll need enough for the length of the border you are making. The manual that comes with the curb machine will give you the formula to estimate how much cement and sand you need for the curb length. Add enough water to the cement and sand to make a thick mud. Avoid making the mix too soupy or the curb won't hold its shape. Don't allow the mixture to get so thick that it clogs the machine.
Align the curb machine at one end of the ditch so the wheels are toward the opposite end of the ditch. The extrusion port opens toward the beginning of the ditch. Keep the mixer or wheelbarrow full of concrete close to the ditch. A helper will have to keep shovelling wet cement into the curb machine's hopper as you move along the extruding curb. Attach the curb template in the shape you want to the extrusion port. This will shape the curb as the concrete is extruded.
Load the reinforcing wire into the feeder mechanism in the extrusion port according to manufacturer directions. Unroll and straighten the wire and lay enough in the ditch all the way to the end. This prevents the wire form kinking as it's fed into the centre of the curb by the machine. Fill up the curb machine's hopper.
Stand facing the extrusion port, grasp the handles of the machine and pull the handle of the rammer. As you do so, the machine will push curb from the extrusion port and the machine itself will begin crawling backward along the ditch while it feeds the reinforcing wire into the concrete curb in one smooth operation.
Move along the ditch with the curb machine. Try not to stop. You want to finish the curb section in one pass. Your helper must keep steadily shovelling concrete into the hopper as you go.
Smooth the damp curb with the concrete trowel to remove ragged edges and rough spots. With the flat edge of the trowel, slice the curb or border halfway through every 3 feet. This creates an expansion joint that will allow the curb to flex without cracking if the ground shifts or you get extreme temperatures.
Stain the concrete if you are going to colour it before the concrete sets. Follow the instructions that come with the staining kit. Now is also the time to cut patterns or apply stamping tools. When you're done decorating your border, let it sit and cure for 24 hours before touching it or putting weight on it. Wash your tools and the curb machine thoroughly.
Tips and warnings
- If you are mixing in a wheelbarrow, lay cement bags and piles of sand along the track of the curb so your helper can mix it more quickly and keep up with the curb machine.
- Try laying a short length of curb on a flat surface where you can pick it up and throw it away. This help you get a feel for the machine and it lets you test the thickness of the concrete mix. Wait 10 minutes and check to see if the curb section slumps or distorts because the mixture is too wet. Scrape up the practice section and toss it. Don't try to run it back through the curb machine.
- Check that you have more than enough cement and sand when you start the job. If you have bags of cement left over at the end, simply return it for a refund.
- Pour the border in one pass to avoid creating ugly seams where you start and stop.
- Wear leather gloves and eye protection to protect your hands and eyes from the harsh cement dust.
- Carefully watch the reinforcing wire as it feeds into the curb machine. If it kinks, the wire can buck up out of the surface of the concrete.
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