Preparing the Foundations

1. Remove any plant growth from the area, including weeds and tree roots.
2. Mark out the area with pegs and string, setting the string at the final surface level.
3. Dig out the area to a depth of about 20 cm (8 in). This will allow for a 10 cm (4 in) layer of hardcore plus a 10 cm (4 in) thickness of concrete. Peat and heavy clay soils can shrink in dry weather, reduce the effect this may have on the concrete surface by excavating a further 5 cm (2 in) and increasing the depth of the hardcore to 15 cm (6 in).
4. Tamp the base of the site down with a plate compactor.

Creating the Framework

You will need to make a frame to keep the concrete in place whilst it sets.

Insert 5x5 cm (2x2 in) pegs into the base every 1 m (3 ft) along the perimeter of the site, so that the tops are level with your string guides. Use a plank and spirit level to ensure that they are absolutely level.

Line planks of wood up against the inside faces of the pegs, making sure that they are level with the top of the peg. Nail them into place to form a framework to confine the concrete until it sets. The planks should be 2.5 cm (1 in) thick, and at least the depth of the concrete (10 cm or 4 in).

Frameworks for curves may be made in much the same manner, although you will need to set the wooden pegs closer together. Smooth curves may be made by soaking lengths of softwood in water to make them pliable and then bending and nailing them to the pegs. Alternatively, you could use several thicknesses of thin hardboard, which is easy to bend and shape.

Preparing the Sub-Base

Spread a 10 cm (4 in) layer of hardcore over the area and compact it with a roller or stout timber. Lay a damp-proof membrane (dpm) over the area, making sure that it extends all the way up the frame walls. Any joints should overlap by 35 cm and preferably be taped. The dpm will prevent the concrete from drying out too quickly (causing surface cracks), and will also protect the underside of the slab from attack by dampness and chemicals in the ground beneath.

Expansion Joints

You must include a number of breaks within the concrete to allow it a degree of movement - otherwise it will crack. Divide the area into small sections no more than 4 m (12 ft) long using planks of timber. Use hardboard if you are using a ready-mixed concrete that must be used all at once; leave this in position until the concrete has set.

Laying Concrete

Use an in situ (poured) concrete mix as follows:

• 1 part cement
• 2 parts sharp sand
• 4 parts 20 mm (3/4 in) aggregate

Alternatively, use 6 parts combined aggregate ('ballast') to 1 part cement, and omit the sand.

Start by adding about half a part of water to one part of dry ingredients to produce a very stiff mix. Gradually add more water until you reach the consistency you need.

Make up the concrete in batches and pour it into alternate 'bays' of the framework. Spread the concrete so that it is level and just proud of the formwork, working it well into the edges. Tamp down the concrete with a length of wood that spans the width of the frame, compacting it with a downward chopping motion. Slide the beam from side to side to level the surface. You may need to fill in any hollows that appear. Level again using the wooden beam, or a wooden float to achieve a smoother surface. A steel float will produce a smoother surface still.

However, do bear in mind that a smooth concrete surface can become quite slippery, especially in wet or icy conditions. It is recommended that you add some sort of texture to the surface once it has been smoothed if you intend to walk on the concrete surface - see Texture (below). Concrete foundations should be left rough to provide a key for subsequent layers.

Lay a waterproof covering such as plastic sheeting over the concrete until it dries. Once the concrete in these bays has set, remove the wood dividers and repeat the process with the remaining bays.

Texture

You may decide that you want to add some texture to your concrete path; this may be done in a number of ways.

• Smooth brushed finish: After tamping the concrete, gently run the bristles of a soft broom over the surface. Running the brush across the path at right angles to the direction of travel will improve traction during wet or icy weather.
• Ridged brushed finish: Once the concrete has begun to set, push a stiff broom over the surface.
• Stamped patterns: Shapes may be stamped into the surface of the concrete using special tools or even objects found around the house or garden, such as seashells or pastry cutters. You can also press large leaves such as horse chestnut or sycamore into the tamped down concrete to create attractive leaf impressions. Leave them in place whilst the concrete sets, and then brush them out with a stiff broom.
• Exposed aggregate: Add gravel or crushed stone to the surface of the concrete before it sets. Tamp it down gently into the surface. When the concrete is nearly hard, expose more of the stone by brushing the concrete surface with a stiff broom. Wash the fine particles away with water and then leave to set.