How to lay concrete
Concrete can be used directly for paths and driveways and as a base e.g. for sheds. A timber frame called a formwork is utilized to help lay concrete. The formwork holds wet concrete and can be used to level the surface and compact concrete.
•You should allow yourself time to do the job properly rather than rush laying concrete.
•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 curing 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 of concrete can be laid.
•The majority of repairs can be carried out using a small diamond-shaped pointing trowel.
Calculating volume of ready-mixed concrete 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 (see calculator).
•Note: you may also need to consider additional features of the job e.g. slope, drainage, accessibility etc.
Health and safety
Suitable clothing including impervious gloves, long sleeves, eye protection and boots should always be worn when handling concrete.
•Garden spade & shovel
•Fibreboard filler strips for expansion joints
Preparing the ground or 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. The ground should be leveled and well compacted using a small garden roller or a compactor to provide a base for your concrete.
Assembling your formwork
The formwork is made up of timber planks 1.5” 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 for the concrete. 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 level to check.
Laying your sub-base
A layer of hardcore of a minimum of 3-4 inches is needed for a sub-base and should be well compacted.
Pouring the concrete into your area
Spread the concrete between the forms slightly 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 of the concrete 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.
Finishing the 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.
Concrete should not be laid in very cold weather or in rainy conditions.