Concrete can be used directly for paths and driveways and as a base e.g. for sheds. A timber frame called a formwork is utilised to help lay concrete. The formwork holds wet concrete and can be used to level the surface and compact it.
Using ready mix concrete
- You should allow yourself time to do the job properly rather than rush it.
- However, you must go straight to work when the concrete is mixed!
- You should plan to use ready-mixed concrete within two hours; otherwise, if it dries to quickly in time it may cause cracks. You should dispose of any material left after 2 hours.
- To permit slow drying, you need to lay polythene sheeting over your concrete. Full drying and hardening can take between four to ten days, depending on weather conditions.
- Concrete may deteriorate in thinner sections. For long term sustainability, it is advisable to increase the area in need of repair so that a thicker layer can be laid.
- The majority of repairs can be carried out using a small diamond-shaped pointing trowel.
Calculating the volume of ready-mix required for your project
- As a guide, multiply length x width x depth of the space you need to fill. This will calculate a cubic size (or volume), of concrete required.
- Note: you may also need to consider additional features of the job e.g. slope, drainage, accessibility etc. It may be best to talk to your local sales office team with details on the area to be concreted for advice.
Health and safety when working with concrete
Suitable clothing including impervious gloves, long sleeves, eye protection and boots should always be worn when handling concrete. There is always a risk to manage to ensure the safety of the people involved, no matter the size or location of the job. We strongly recommend that you take the time to read our Concrete Health and Safety Datasheet.
- Spirit level
- Builder’s square
- Lump hammer
- Garden spade & shovel
- Heavy roller or wacker plate
- Strong wheelbarrow
- Ready mix concrete
- Timber planks
- Fibreboard filler strips for expansion joints
- Wood preservative (if required)
Damp-proofing of concrete
- Use polythene sheeting thicker than 0.010” (known as 1,000 gauge).
- Spread the sheeting over the sub-base, ensuring the edges are turned up at the wall to form a tray.
- Where there are joints; ensure they are overlapped and secured with waterproof tape. Please contact your local sales office, when you need watertight concrete or jointing materials.
Preparing the concrete base
The preparation needed will depend on the existing surface and what the concrete will be used for. Measure and mark out the area you need to concrete, using a string line and wooden pegs, ensuring that the corners have a 90 degree angle. As a rule; your base must be 75mm larger that the finished slab to allow for formwork. Clear the area of stones and plants and excavate to a minimum depth of 100mm (deeper for soft ground). The ground should be levelled and well compacted using a small garden roller or a rammer to provide a base for your concrete.
Assembling your concrete formwork
The formwork is made up of timber planks 25mm thick that go around the edge of the area you want to concrete. This will support the concrete as it hardens and also is used to form a level. When building your formwork it is important to remember to allow for run off letting water to drain from the surface and to knock some of the timber planks in deeper than others - use a spirit level to check this. As a guide, an area of concrete 2m wide should have a drop of 25mm to prevent standing water. If you are laying a circular concrete base, you could use rope or a hosepipe to mark the outline of the curve you want to follow. The pegs and string will need to be closer together to maintain the curve and the timber will need to be cut to about half its depth on the side that will form the inside of the curve.
Laying your concrete sub-base
A layer of hardcore of a minimum of 100mm is needed for a sub-base and should be well compacted.
Pouring the concrete into your project area
Spread the concrete between the forms 10-15mm higher that the finished surface and compact it down using a tamping beam. Choose a piece of wood with a good straight edge ensuring it’s longer than your form. With one person at each end, raise it above the form and bring it down. Ideally this process should be repeated twice. In order to level the concrete use a sawing motion with the tamping bar across the surface whilst moving forward. Ensure that the concrete gets into the corners of your forms and that there are no low spots. If there are then fill these in and repeat the tamping process.
If you are laying a large area of concrete more that 4m wide or long, it is wise to lay it in sections to prevent it from cracking during expansion and contraction. To do this, divide the formwork into bays with control joints between the sections of concrete. After each section has been laid you can remove the supports and lay the next section.
Line the base and sides of the area with heavy plastic sheeting to ensure that it stays dry. If you want to concrete a large area please contact your local authority first to establish if you need planning permission.
Concreting a path
Mark out your area as previously described and dig out the path to a depth of approximately 175mm taking care to set your formwork so that it marks the boundary and restricts the concrete, then pour and tamper as described above.
Finishing the concrete surface
Depending on the use there are a number of options for finishing the surface of the concrete. Leaving it as a tamped surface will provide a low-slip surface suitable for drives and paths. To achieve a smooth surface suitable for house floors, ponds etc you can use a float which is a flat piece of wood or metal that you can draw across the surface of the concrete. A float or a shovel can be used to create fish scale effects by using circular movements across the surface of the concrete. Using a broom head you can create a brushed effect which indents the surface without pulling it apart...
Let the concrete set
Cover the concrete with polythene sheeting weighted down at the edges to prevent it from drying out too quickly and leave for ideally seven days in summer and ten in winter to allow it to cure before removing the covering. Allow an additional day before removing the formwork to ensure that it is set.
READY MIX TIP
The addition of polypropylene fibres can enhance the concrete mix and reduces the need for crack control wire mesh and produces longer lasting concrete. It also makes the concrete impact and abrasion resistant and has an enhanced surface finish.
Concrete should not be laid in very cold weather or in rainy conditions. If it rains before the concrete is hard enough to cover directly with a sheet, build a frame to support the sheet to prevent it from touching the surface and causing damage.