Basically, a driveway, path, patio or terrace is constructed in the same way. Differences are largely in the strength of the finished surface. A driveway which has to carry the traffic of a car needs to be stronger and capable of taking more wear and tear than a terrace, where the load is no more than garden furniture and the weight of people.
While driveways and paths have a different function from patios and terraces, all such features should enhance the appearance of the house and its surroundings. For example, a driveway of modern concrete paving slabs may look out of place in front of a period cottage but could appear attractive in the garden layout of a modern semi-detached home.
Success in constructing these features lies in quality of the foundations. First, these must be firm. Secondly they must be adequate to receive the final surface layer. Material laid on bare sub-soil may in time, with the effects of weather, move and subside, causing the surface to crack and become uneven. The type of foundation, therefore, depends on the stability of the sub-soil, the material to be laid and the use to which the surface is to be put.
Types of surface
Concrete, while functionally suitable equally for patios and terraces as for driveways and paths, can appear harsh in a garden setting. This can be corrected by using aggregate chips or a colouriser in the concrete to give a softer decorative look. Wet-mix concrete is normally poured between wooden frames, called shuttering, to the required depth.
Slabs embedded in mortar or sand. A mortar mix can be used as a sub-surface on which to lay stone or concrete slabs. These may vary in texture and colour. Inlaid into the mortar bedding, they form a solid, durable surface. Slabs may be laid on to a bed of sand or brick rubble and sand.
Stepping stones provide an informal, attractive form of pathway and can be laid across a lawn. Stone slabs can either be laid directly on to the grass or bedded into a levelling screed of damp sand. For a planted path, you can lay stones directly on to well-tamped sub-soil, leaving gaps between the stones. Fill the gaps with topsoil and introduce suitable ground-cover plants. The effect can be attractive, provided you keep the path well maintained and weeded. Tarmacadam or asphalt. Cold-rolled or hot-rolled asphalt or bitumen is suitable for paths and driveways if the sub-surface is correctly prepared. These materials are easy to lay and give a professional finish.
Brick. Bricks are suitable mainly for garden paths, patios or terraces not subject to heavy traffic. They can be laid “frog” (the indent in the brick) downwards or laid on edge. Use heavy engineering or paving bricks rather than conventional bricks.
Stones inlaid in concrete. This type of surface combines the strength of concrete with the textured beauty and colour of natural stone. Quarried stone, stone paving slabs, exposed-aggregate slabs, cobbles or even slate may be used.
Mortared broken paving slabs. Mortared at the edges, these provide a cheap and durable paving surface. If the foundations are firm, it can take the weight and movement of a car.
Gravel paths and driveways produce a natural-looking surface suitable for light traffic. For a gravel driveway, make sure the foundations are at least 6 in. (or 150 mm) deep.
For site levelling and concreting you need the following tools: shovel, spirit level, garden rake, wood float (for finishing), two hammers (claw and club), string line, tamper and tamping batten, stiff broom and levelling pegs 3 in (or 7.5 cm) long. A tamper can be made from a scaffold board, with wooden handles at each end, so that it can be used on end by two people. A tamping batten can be made from a piece of stout timber.
After pegging out remove topsoil and vegetable matter, including all roots. Dig out the site to the depth of any hardcore needed plus the thickness of the final surfacing. Allow about 3 in (or 75 cm) depth, on average, for hardcore. If the subsoil is not firm, the excavation must go deeper than if it is, particularly if the finished surface is intended for heavy traffic. For carports or hard standings, the concrete slab and excavation should be at least 4 in. (or 10 cm) deep with 3 in (or 7.5 cm) of hardcore.
If the driveway or path adjoins a building, ensure that the final surface level is at least 6 in. (or 15 cm) below the damp-course.
Hardcore can usually be obtained from builders’ merchants. Specify that it is “good clean” hardcore to ensure that the material is of even size and free from plaster rubble. A good hardcore foundation will compact evenly and give a stable foundation layer. To ensure this, tamp down the hardcore firmly and evenly. Apply a liberal dressing of aggregate “blinding” to cover the hard-core. Then tamp again thoroughly.
Preventing weeds. Apply a solution of a proprietary weed-killer, such as sodium chlorate, to the base of the path or drive, keeping this damp while you are filling in the excavation. Dry sodium chlorate is flammable; if possible, obtain sodium chlorate with a “fire depressant” additive. Setting out. Mark out the perimeter of the site with simple wood levelling pegs. Measure between these and set up string lines. Excavate to the required depth and fill in soft patches with small stones and rubble. Tamp down or roll the site well. Cut a number of wooden pegs about 3 in. (or 7.5 cm) long and set these out on the site at intervals. Use a spirit level and straight edge to check the levels between them and make any necessary adjustments. Ensure that any fall or slope is away from buildings.
Concreting For A Driveway Or Path
Shuttering or formwork must now be positioned along the edges of the path or drive. This consists of boards at least 1 in. (2.5 cm) thick. A number of stout pegs, spaced at intervals of about 3 ft 6 in. (or 1 m). should be knocked into the ground on the outside of the boards and nailed on to hold them in place when concrete is poured Level across to the shuttering on the other side of the path or drive. The top of the shuttering is the level of the concrete or other surface. The shuttering can usually be removed after about five days.
Weather conditions. Concreting should be avoided during heavy frost, when entrapped water freezes, expands and causes the concrete to crack. Concrete may also crack in very hot weather; to avoid this, keep the newly laid concrete moist, cover it with sacking and spray it with water. The best weather for concrete work is cool, slightly overcast and dry.
Mixing. Concrete is a mixture Of three materials: cement, sand and gravel aggregate. These materials are mixed in different proportions for different purposes. A mix of one part of Portland cement, the basic cement used in concrete work, two parts of sand and three parts of aggregate, formulated as 1:2:3, is needed for paths. For drives and hardstanding use, 1 :21:4 is the common formula.
Mixing by hand. You need a firm, clean base, such as a sheet of metal, a concrete slab or piece of plywood. Since concrete leaves stains, do not mix it on existing paths or similar surfaces.
1. First, measure out the materials “dry” in the correct proportions.
2. Mix the sand and aggregate thoroughly.
3. Add cement to the heap, mixing it in until an even colour is achieved.
4. Make a hollow in the middle of the pile and pour water into it from a watering can, so that the flow can be gauged. Never use a hose as the force of water will separate the aggregate and weaken the mix.
5. Turn in the materials from the outside of the crater into the middle, mixing thoroughly. Add water sparingly until the concrete has a smooth “plastic” look.
6. Flatten out the mix with the back of a shovel and then jab several times with the edge of the shovel to make ridges. These should stay in place and not “slump”. Another test is to press the sole of your shoe lightly against the mix; it should remain close-knit and not show excess moisture.
Using a mixer. If a fairly large volume of mixing is involved, hiring a concrete mixer will save you time and much hard work. Mixers are powered by petrol, diesel or electricity.
1. Start the machine and pour in a bucket of water to lubricate the bowl.
2. Put into the bowl all the cement and sand and half the aggregate. Allow these to mix, adding, as needed, a little water.
3. After about half a minute, add the remaining aggregate.
4. When the mix has a smooth “plastic” appearance, it can be poured. The bowl is in a near-upright position when running; a wheel on the side of the machine enables the bowl to be locked in various positions. Ready-mixed concrete. For really large areas, ready-mixed concrete may be the answer. It will be delivered by a big mobile concrete mixer, so make sure that the vehicle can back on to the site. A quantity of concrete tipped some distance away may “go off” before it can all be moved to the actual site.
Additives. Additives may be mixed with concrete to accelerate hardening, to assist curing in cold weather or to inhibit the setting process. Particularly in hot weather, cracking may occur as concrete expands. For areas exceeding 10 ft (3 m) concrete should be broken up with expansion strips. Strips of timber in. (6 mm) thick, dipped in creosote, should be embedded to the depth of the concrete. An alternative is to set in temporary thin timber strips, ‘removing these later and filling the gaps with bitumen. Laying concrete. Concrete should be spread evenly between the shuttering and levelled across with a long board. Lay only small sections at a time. Draw off any excess concrete with the board. Use the tamper to firm down the concrete but do not try to achieve a smooth finish, for this could be slippery and hazardous in wet weather.