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Concrete and Asphalt Paths
Concrete and asphalt paths remain one of the most popular hard surfacing materials. They are long lasting, and if laid properly, perhaps the easiest surfaces to maintain. Concrete and asphalt can be real alternatives to pavers and in many cases are a lot cheaper. Their main drawback has been their plain, utilitarian appearance, but as this article shows, there are several things that can be done to turn concrete and asphalt paths into attractive garden features.
Concrete or asphalt?
Apart from appearance, there are several differences between the two materials. Concrete is smoother, harder and more durable, but it is difficult to lay on steep or very uneven sites, and is generally quite expensive. Once laid, it will maintain its shape without uneven settling. A range of finishes can be applied (see below) to enhance its appearance.
Although asphalt is less durable, it can be more readily patched or repaired, and does not require as much site preparation prior to laying. It is generally less formal in appearance than concrete. The choice of finish is much more limited than concrete, with colouring being the only option (the most popular colour being earthy tones).
Both types of paths will work better with the following:
· A well prepared, solid base is essential to prevent movement after the material is laid. Typically concrete and asphalt are laid on a base of compacted soil covered with a layer of crushed rock.
· If the area has drainage problems, sub-surface drains should be installed before the path is constructed to reduce soil movement. The final surface should have sufficient slope and be free of depressions to prevent pools of water from forming. This will reduce the likelihood of creating slippery surfaces or of getting wet feet when you walk on it. Provision should also be made to dispose of the water that runs off, perhaps by running it into an underground stormwater drain.
· Suitable edging. Usually a brick, stone or timber edge is pegged or concreted into position before the material is laid. This edge needs to be permanent for asphalt, but can be removed from concrete after it has set hard. Other possible edges include railway sleepers, preformed concrete drains, bluestone pitchers and pre-packaged plastic or timber edging. The choice is yours, but the style should complement the surface it edges and the surrounding of the garden.
Laying a Concrete Path
1. Dig out the area to be concreted, usually to a depth of 15 cm.
2. Compact the base with a roller or ramming machine.
3. Add a layer of gravel, stones or sand (6 to 8 cm deep), rake over to obtain required levels and then compact with a roller or ramming machine (“wacker”).
4. Build the formwork by pegging wooden planks (e.g. 100 x 25 mm timber) along the sides of the path, with the top of the planks set at the final level you intend for the path (allow for concrete to be at least 6 cm thick; and much deeper if vehicles are to be driven over it).
5. For areas that will handle medium to heavy traffic (eg. vehicles) it is important to include steel mesh for added strength. For most walking paths this may not be necessary.
6. Pour a small section of concrete at a time. Use a long smooth board rested on the side planks for levelling. Using a sawing motion, gradually move the board along the side planks, moving the concrete to achieve the required level and creating as smooth a surface as possible.
7. Sprinkle a mixture of sand and cement (4 to 1) over the surface of the path and using concrete trowels smooth the surface to remove any holes or blemishes.
8. Using a metal bar, make an expansion join at least every 1.5 to 2 metres along the path. (This is an indentation in the surface to prevent cracking due to expansion and contraction in different weather.)
9. Cover the path with moist hessian for around 7 days to prevent concrete.
10. Remove the formwork after the concrete has fully dried.
CONCRETE MIX FOR PATHS AND DRIVEWAYS:
2 parts cement : 3 parts sand : 5 parts stones (approximately 12mm aggregate)
HOW LONG DOES CONCRETE TAKE TO SET?
After 2 hours: Workable; no strength at all.
After 3 days: No longer workable, still has very little strength, easy to damage.
After 7 days: Solid, still only half strength.
After 30 days: Very solid, full strength.
HINTS WHEN CONCRETING
*Concrete is stronger if it dries more slowly.
*Covering with damp hessian or wet newspaper will slow down the drying rate.
*Setting retardant chemicals can be added to slow down the rate of drying.
*It is preferable not to lay concrete in very hot, rainy or frosty weather.
*If it rains, fresh laid concrete should be carefully covered with black plastic sheeting.
Concrete can be finished the following ways to create different effects:
· Adding pigment to change the colour.
· Brushing the surface lightly with a stiff broom to create a non-slip surface.
· Using stencils or moulds to simulate the appearance of pavers or cobblestones.
· Creating a pebbly appearance by exposing the aggregate (either while the path is being laid or adding a layer of aggregate before it sets).
· Edging the path with bricks in a contrasting colour.
· Placing bricks at intervals across the path to break up the bulk of the concrete.
Traditional black asphalt has made way for more modern colours, such as red, green, cobalt, gold and similar tones, allowing asphalt to “fit into” a wider range of gardening styles.
The benefits of asphalt include:
· It does not reflect glare
· It is hard wearing
· It is fairly easy to keep clean
· It is easily patched
· It is easily extended or altered to cater for alterations in garden design.
Laying asphalt is a specialist task that is best left to the “experts”.
· Asphalt can be prone to minor damage like indentations and scuffing in the first two years after laying, until it settles down. This is easily prevented by cooling down the bitumen with a hose or sprinkler during periods of extreme heat and heavy use.
· Some grasses and weeds (like nutgrass) are known to grow through an asphalt path, so it is important to spray these pest plants with weed killers.
· Avoid oil and petrol spills on bitumen as these can result in weakening of the bitumen surface.
· Dips or lifts (from roots or soil subsidence) are easily dug up and replaced with similar material, preferably by the same contractor who laid the pathway originally.