Pouring a Path

Awkward little spaces around the outside of a house can be difficult to use creatively, but a pathway can look good and be practical without breaking the bank. What’s more, they’re easy to lay with some basic DIY skills.

After clearing the area where your path is to go, you need to run a string line along one edge of its proposed line. This needs to be put in place at the height that the path is going to be finished. This will allow you to excavate the surrounding area to the required depth and width before fixing the formwork in place and pouring the concrete.

For most paths, excavating to a depth of 75mm is adequate in order to provide a firm foundation for the concrete. Clear the area adequately and get to work on building the formwork (or boxing). Use a sledgehammer to drive a peg in behind the formwork at each end of a length of timber, ensuring it is in line with the string line, and then nail it in place to the correct height.

To make it easier to nail your formwork to the peg, hold the head of a sledgehammer behind the peg when driving the nail into position.

When both section ends are secure, run a tight string line across the front face and along the top to ensure the formwork is both straight and level. Once the string line is in place, lift it out from the surface by sliding a couple of packers (all of the same thickness) between the string line and the formwork.

For the other side, run a second string line where the edge of the path will be and repeat the process to fix the second section of formwork into place. Ensure accurate spacing between the two sections with a length of timber the width of the path.

Once this is done, secure a stop-end in place at the end of the path.

The next job is to remove any fill from inside the path to the required depth. Sit a piece of timber on the top of the formwork and measure below it to check if the path is deep enough (at least 75mm).

Exposed aggregate requires a special mix of concrete. Ready-bagged, pre-mixed concrete normally uses a builder’s mix with an aggregate size of around Gap 20. This means that the pebbles in it can be as large as 20mm in diameter, which isn’t really suitable for an exposed aggregate finish. It’s possible to obtain pre-mixed aggregate/sand combinations in smaller quantities with pre-bagged product.

If you are planning on mixing your own concrete, you’ll need Golden Bay Cement, which is great general-purpose cement suitable for this type of job. Available in useful 40kg bags, combine with builder’s mix at a general ratio of one part cement to five parts builder’s mix with just enough water to make it pliable, but not sloppy. Adding too much water will make the final concrete weak and, when it has cured, the surface is likely to be dusty.

For small mixes, it’s possible to mix it by hand in a wheelbarrow; for larger mixes, like this job, it’s more efficient to hire or buy a concrete mixer.

When placing the concrete, tamp it in place using a rake to remove any air bubbles and then screed it off using a straight piece of timber across the top of the formwork. Remove the build-up of concrete from in front of the screed as you work it along, but leave a small ‘wave’ of concrete slurry in front of the screed. If you come across any low patches, add concrete to the area then re-screed until it’s level.

Once the surface water has evaporated, but before the concrete has started to ‘go off’, a retarder needs to be sprayed onto the surface if a successful exposed aggregate surface is to be achieved. A retarder, like Sika’s Rugasol C, is available as a ready-to-use liquid. This is designed to slow the curing of the surface of the concrete.

Using a hose and a soft broom, the retarded concrete surface can be removed, exposing the aggregate underneath. Before undertaking removal of the entire surface, check it on a test area first to ensure the concrete is hard enough to hold the aggregate in place.

After the concrete has cured for at least 24 hours, the formwork can be removed, taking care not to crack the edges and corners.

Estimating concrete

Concrete quantities are measured in cubic metres (imagine a cube 1m wide x 1m high x 1m deep), as are the aggregates or sands that are included in any concrete mix.

To estimate the volume of concrete needed for a project, multiply the length by the width to calculate the area of the project and then multiply this number by the depth or thickness to calculate the amount of concrete required.

Remember this needs to be done in metres.

For example, a path 5m long and 750mm wide has a surface area of 3.75m² (5m x 0.75m = 3.75m²). If the path is 75mm thick, multiply the surface area by 0.075 to calculate the amount of concrete required (3.75 x 0.075 = 0.28125m³).

In this case, to allow for any extra concrete that may be required, it would be easiest to round it up to 0.3m³, just to allow for a little bit of waste.