Concrete is one of the easiest building materials to work with. Follow these step-by-step instructions on how to lay your own concrete.
Materials checklist
Sharp sand
Stone aggregate
Dry cement or ready-mix concrete for small jobs
Steel reinforcing - F52 for 100mm thick concrete (driveways, etc)
Steel reinforcing - F42 for 75mm thick concrete (paths, etc)
Bar chairs - 50mm for 100mm thick concrete
Bar chairs- 40mm for 75mm thick concrete
Formwork timber - straight boards at least 25mm thick and as wide as the concrete's depth
Stakes 50mm square and long enough to cover depth of concrete plus about 300mm for driving into the ground
50 x 2.8mm bullethead
Sheet of plywood or hardboard
Sacking or polythene sheeting
Concrete is one of the most versatile building materials. It lends itself well to a wide variety of shapes and forms. You can use it to create a family entertainment centre, build a patio, garden path or driveway, or provide a hard and durable floor that will last a lifetime in your garage, workshop or garden shed. There’s no need to hide behind the excuse that you’ve never concreted anything before either – concrete is also one of the easiest building materials to work with. The techniques for laying anything from a shed floor to a garden path are much the same, once you know the basic rules for mixing up the ingredients, making formwork, laying and levelling. And in this MitrePlan Project Planner, we provide you with the know-how. Just follow the step-by-step instructions and you’ll find working with concrete relatively simple. All you need are the right tools and the right materials from your Mitre I0 specialist – and you’re on your way.
Step 1: let's plan ahead
Unlike most building materials, concrete is hard to dispose of if you make a mistake. So plan your job carefully. Make a sketch of it if necessary. What you are concreting is also an important consideration. For example, you may want to use ready-mixed concrete if you are laying a large driveway or garage floor. This is delivered in bulk by large trucks, so you must have formwork in place and a couple of helpers ready to off-load it. It is also sensible to check with your local authority before starting about any regulations or restrictions, particularly in relation to existing drains or pipe runs.
Step 2: buying your materials
Concrete is made by mixing cement, sand, stone aggregate and water. For small jobs, it’s best to buy pre-mixed concrete in 40kg bags. Then all you do is add water. For larger projects, it’s cheaper to buy the materials separately and mix yourself. Cement is normally sold in 40kg bags. Sand and aggregate are both sold by the tonne or fraction of a tonne - the minimum is usually a quarter of a tonne.
Different projects require different thicknesses of concrete and the mix must be adjusted accordingly. Basically, the greater the load on the slab the thicker it must be. Here are the most common mixes:
Suitable where a minimum thickness of 100mm is needed, such as driveways, garage and workshop floors, - one part cement, 2 1/2 parts sand, four parts aggregate.
Used for light duty strips and bases up to 75mm thick - garden paths and the like, - one part cement, two parts sand, three parts aggregate.
Where great strength is not needed, such as garden wall foundations, bedding in slabs, and so on, - one part cement, three parts sand, six parts aggregate. To calculate the volume of cement and aggregates needed, multiply the area’s length by its width by the required thickness of concrete. Then use this handy guide to estimate your quantities, allowing for wastage by rounding up volumes to the nearest half or whole cubic metre.
Mix, Cement, Sharp Sand, Aggregate To make 40kg
Step 3: preparation
First, measure and mark out the area to be concreted. Stretch stringline between pegs driven in the ground, then remove the top soil until you’ve accurately marked out the shape of the area. Use a builder’s square to set the corners accurately. Then dig down to the depth you want the concrete. The prepared area should extend about 150mm beyond the edge of the finished slab so there is space for preparing the formwork (Fig. 1). Be sure the ground is firm, level and free from vegetation. If it is soft and loose, add a layer of stones or broken bricks and tightly compact into the surface with a sledge hammer. If laying immediately over an old concrete base, completely break up the old first and compact it or your new concrete will also crack.
This is a kind of box that keeps the concrete in place while it hardens and provides an edge for levelling the poured concrete. Hammer in pegs at 1m intervals around the outside of the entire area. Place the formwork boards against the pegs using your stringline to accurately align them. Use a spirit level to ensure the tops will be flush with the finished level of your concrete. If required, check that the formwork is slightly lower on one side so rainwater can run away. If near a home, slope away from the house. Then nail the boards to the pegs making sure there are no gaps between boards, or boards and ground where concrete can seep through.
Step 5: mixing the concrete
At this stage, you should also consider adding a colouring agent to your mix. Liquid and powder forms are available in a range of earthy colours to highlight the overall design of your path or driveway.