Concrete is made by mixing cement powder with water to form a paste that bonds gravel, which makes up 60 to 80% of the volume. Mix it up in a wheelbarrow, but for bigger jobs use a cement mixer. Concrete is measured in cubic metres and 1m3 covers about 10m2 at 100mm thick.
Work out how much you need, round it up to m3 and add an extra 0.2m3. A minimum premixed order is 0.4m3, and most large concrete trucks can carry 6m3. For a pathway, order N20/10, where N is normal concrete, 20 refers to strength in megapascals (mpa) and 10 is the aggregate size (10mm). Concrete can burn skin on contact, so wear gloves, sleeves, long pants and gumboots, and be sure to wash concrete off skin immediately.
Build solid formwork
Use 90 x 45mm or 70 x 45mm timber for the vertical edges, and 50mm2 hardwood pegs with steel bands around the top to prevent splitting, with the length determined by the soil type.Use 75mm bullet-head nails to fix the formwork to the pegs. If the formwork extends below ground, pack soil against the pegs. If it extends more than 150mm above ground, reduce spacing between the pegs and brace with a diagonal kicker.
Setting the curve
Reinforcement is required to prevent curves bulging. Use flexible oregon offcuts of 100 x 10mm that are bundled and sold cheaply at many timberyards, or sheets of 4mm bracing ply for about $27, which is easily cut with a circular saw. 2 If the formwork is underground, position pegs 900mm apart, packing soil against them. For above-ground formwork, space pegs 450mm apart. To keep the sides parallel, build one side then use a gauge board of 90 x 19mm with spacers attached to position the other side.
Put down a solid base
A firm, well-drained base is the key to a crack-free path, achieved with compacted soil underneath a 100mm layer of road base material. Pack the base with a hired plate compactor ($80 for half a day) measuring the base height down from the finished concrete height. Spread a 20mm layer of sand over the base to eliminate friction between concrete and base.
Position the pegs
Cut back the pegs projecting above the formwork, as they tend to obstruct the screed board. If the formwork is near ground level, check the screed board doesn’t drag on the ground, skimming off dirt to clear a path for a smooth finish.
Eliminate air pockets
When the concrete is poured, air pockets are trapped against the formwork, leaving voids in the vertical surfaces that can bubble and leave holes. Use a 70 x 45mm post to plunge along the formwork then tap the formwork with a hammer to expel air and settle the concrete. Pack the concrete along the edges with a timber float then screed the surface using a sawing action.
Float after screeding
After screeding, smooth the concrete in both directions with a hand float, which forces down the aggregate and pulls the cement cream to the top for a smooth surface. 6 Floats are made from timber or steel for different finishes. Use timber for a rough, slip-free surface and steel for a smooth finish. For a long path, hire a bull float. The long handle extends reach and the broad head covers the surface flatten to smooth bumps.
TIP: If puddles of water form on the surface after screeding, wait for them to disappear before floating.