Instructions

Concrete is strong, versatile and inexpensive. It’s also easy to mix and use. This step by step guide is all you need to plan and complete simple concreting projects around your home.

Put Your Ideas Down On Paper

The more preparation you put into your project, the better you’ll feel about the result. Small jobs don’t need a lot of planning. But bigger projects, like driveways and patios, require a bit more thought. It’s a good idea to make a sketch plan of your project before you start.

Concrete Paths

For major paths be generous about width - aim for 1.25 metres or more. 0.5 metres is wide enough for secondary paths. Your path should be at least 75mm thick. If the path is to be against the house slope it away from the house so water can drain away. A fall of 1 in 25 is an effective slope.

Yards & Floors

A large area of concrete can be laid in exactly the same manner as a path, simply by laying strips about 2 metres wide. It is best to lay strips alternately, removing forms and filling in the remaining sections when the first strips are hard.

Hardstands & Driveways

The minimum width for a drive is 2.4 metres, or two strips 750mm wide with 900mm space between. To withstand the weight of vehicles a driveway must have a well compacted sub-base. You should plan to make the concrete at least 100mm thick. If you’re laying the drive on clay or other poor soil, increase the thickness to 150mm.

Consider Reinforcement

While reinforcement won’t stop a path or driveway from cracking, it will prevent the breaking up of concrete once a crack has formed. Reinforcing is advisable if the path or drive is to be used by heavy vehicles. It’s also a good idea if the foundation is likely to settle.

A Simple Equation

To estimate the amount of concrete you need, simply measure the area to be concreted and multiply by the thickness you want to achieve. For example, if you’re laying a path that’s 10 metres long, 1.2 metres wide and 100mm (0.1metres) thick, your calculation will be 10 x 1.2 x 0.1. The result is the number of cubic metres’ of set concrete required, ie. 1.2 m³.

The Right Raw Materials

When you know how much concrete you want to make (see table 1) establish the quantities of cement and aggregate you’ll need. Add 10% for wastage. Sand, aggregates and builder’s mix can be stored indefinitely in separate covered piles on a hard surface, but don’t try to store cement for more than a week as it may harden in the bag.

REMEMBER: outside drains only drain RAIN. Remember to wash your tools on the grass (away from stormwater drains). Use sandbags to divert concrete wash water away from stormwater drains to an unsealed area.

Setting Out

Start At Ground Level

Begin by removing all vegetation and topsoil and leveling the ground surface. On most soils concrete can be laid direct on well-compacted ground. For drives and hard stands or when working on clay or peaty soils you will need a 100mm sub-base of free-draining hardfill. Clear the site at least 150mm beyond the edges of the area. Dig out the required depth, allowing a slight slope so that water will run off easily, and compact the soil thoroughly with a mechanical compactor, heavy garden roller or rammer.

Set Up Your Side Forms

The formwork has to be rigid in order to withstand the pressure of the wet concrete. Use old fence or floor boards to provide a form to hold the wet concrete. Nail them to pegs driven into the ground at 0.6 to 0.9 metre intervals. Level the forms with a spirit level.
For curves, make a series of sawcuts in the side of the forms on the inside of the curve; you’ll then be able to bend the form without breaking it. Plywood, hardboard and fibreboard can also be used to form curves. It’s a good idea to brush the inside of your side forms with grease or oil before you pour the concrete to ensure the formwork is easy to remove later.

Setting A Cross-fall

Large areas of concrete should have a ‘fall’ to one side, so that water will run off easily. Aim for a fall or slope of about 1 in 40 (25mm drop per metre run). To get an accurate slope set levels on the high side first. To set the lower level set the low side pegs to match the level of the high side pegs and measure down the required amount.

Set Your Levels

Over short distances levels can be set using a spirit level on a straight edge. Over greater distances a water level will be more accurate than a series of measurements made with a spirit level. If you choose to use a spirit level over long distances ‘end for end’ it after each transfer so that if it is not reading exactly level, the error will be corrected at each alternate mark.

You Can Make Your Own Water Level

A water level is simply a long polythene tube filled with water. If there are no air bubbles in the tube the water will always be at the same level at both ends. Put food colouring or dye in the water to make it more visible and stoppers at each end when not in use. Remove these stoppers when using the water level.

Simple Safety Tips

Concrete is safer to work with than most other common materials. There are two main safety points to remember:

1. Be careful lifting and handling, concreting materials are heavy and you could hurt your back.
2. Don’t let freshly mixed concrete or mortar come into direct contact with your skin. Wear protective gloves. If you do get wet concrete on your skin, wash with soap and water within an hour. If cement gets in your eyes wash immediately with clean water and seek medical treatment.

Machine Mixing

Machine mixing is better for larger quantities:

1. Flush the inside of the mixer with clean water and then drain it out.
2. Place 1/2 the measured water in the mixer.
3. Place 3/4 of the measured aggregate in the mixer.
4. Place all the measured cement in the mixer.
5. Place remaining aggregate in the mixer.
6. Mix for 2-3 minutes, slowly adding remaining water to produce a mix of the desired consistency.

Hand Mixing 

It’s this easy! Hand mixing is appropriate for small volumes.

1. Measure out the sand and gravel into a heap on a hard surface or in a barrow.
2. Make a well in the centre of the heap and add the cement.
3. Mix the materials together thoroughly, aiming for a pile that’s uniform in colour.
4. Make a well in the mixed heap and add some of the water. Bring the dry material to the water from around the edge of the crater. Keep mixing and adding water until the whole pile is well mixed.

Placing & Finishing

1. Be sure that the formwork is ready before you mix your concrete.
2. Dampen the ground where the concrete is to be placed.
3. Spread the concrete evenly between the forms and rake smooth to a level about 15mm higher than the finished surface.
4. Pack down with the back of a rake or shovel. Tap the side of the forms to drive out trapped air.
5. Use a length of 50mm thick timber on its edge as a screeding beam. Level the concrete by shuffling the beam from side to side while drawing it slowly forward. Ensure that both ends of the screeding beam are supported on the top edge of the formwork to ensure the correct level of finished surface.
6. ?For a non-skid surface, draw a stiff broom across the surface of the concrete after the bleed water has evaporated and before it sets hard. Use a soft broom for a finer finish.

The Art Of Jointing

Concrete shrinks as it dries, causing small cracks. By putting joints in your concrete path or slab, you’ll avoid unsightly irregular cracks. The maximum distance between joints should be no more than twice the path width.
For unreinforced concrete slabs, joints should be no more than 3 metres apart. Here are two ways to create joints:

1. Place full-depth strips of timber or hardboard between the side forms.
2. Draw a jointing tool across the path at intervals, creating a neat groove about a quarter of the depth of the concrete. When the concrete is firmer, go over the grooves again. When the concrete dries and shrinks, the cracks will occur at the bottom of the grooves where they can’t be seen.

Curing

Proper curing of concrete is essential to ensure that it gains strength and durability. As soon as your concrete is hard enough not to be marked, curing should begin. For seven days the concrete must be kept moist, either by spraying water onto the surface regularly or by covering the new concrete with polythene or damp sacks. For driveways, wait at least 21 days before you allow heavy traffic to drive on it.

Finishing

Steel Trowel

By using a steel trowel to smooth your concrete you will achieve a very even surface. Be aware that this type of finish can be very slippery when wet and isn’t really suited to paths, patios and driveways.

Brush Or Broom

Pulling a broom or brush over the concrete will give you an attractive non-slip surface. Start “brooming” after the bleed water has evaporated and work quickly for good results. For driveways, brushing across the width will assist drainage.

Shovelback

The back of your shovel can be used to create a non-skid pattern on your new concrete. Wait until the bleed water has gone and experiment on a small area first.

Coloured Aggregate

While the concrete is still soft you can sprinkle the surface with coloured aggregate. The aggregate should be pressed in with a wooden float. Once the concrete has hardened enough for the aggregate to stay in place, use the hose and broom technique to expose the aggregate.

Sponge

A sponge can be used to create an attractive finish which is easy to achieve. Simply press the sponge lightly into the concrete after the bleed water has evaporated. Other finishes include stamp patterning, where you can achieve the look of cobblestones or slate. Using a jointer, imprinting by hand, can create a crazy-paving look. Use your imagination and decorate with shells, tiles or glass chips.

Cleaning Up

Environment

It is important to ensure that your concreting project does not damage the environment. Ensure that you have located all storm water drains around the work area and that these are suitably protected to ensure that concrete wash water and slurry does not go down these drains.
Failure to protect the storm water drains from contamination may result in action from the local authority and may result in a substantial fine.

Tools

Ensure that tools are thoroughly washed to remove all concrete before it sets. Do this on grass or unsealed ground. Remember to protect storm water drains from contamination.