How To Build Concrete Foundations
Whatever you’re building, a shed, garage or a house, you’ll need a sturdy foundation to support the weight of the construction. Even fence posts need a stable base, to stop them sinking into the soft soil below. You may opt to build one foundation system, that covers the entire area that is going to be built up on, or you could opt for a series of individual footings, that each support an area of the build. Either way, foundations are essential to ensure the stability and strength of your project, and finding out which system is best for your build, is the starting point.
It’s a fundamental part of your project and it pays to know the suitability of each type of foundation before you begin digging.
Foundations vs Footings
Footings and foundations are not the same thing; often a large construction project will need both to secure it properly. Footings provide reinforcing support to columns of a build, and sit directly on the soft ground below. A foundation system is actually part of the building, and is usually installed on top of a series of footings to spread the load from the build between the separate support footings.
Construction of concrete foundations
Concrete is the best material for building foundations, simply because it is versatile and very strong. To build the foundation system, first a wooden frame must be built in place as the mould for the concrete. The concrete can then be poured directly into the mould, to fill the required shape. The shape of the foundation system will depend on the type of ground below, the shape of the building and the structural support it requires. Once the poured concrete has cured, the frame or formwork can be removed.
If the project is a large build, it is likely that metal reinforcing bars and cement columns are added with the frame, to provide additional strength to the foundation system.
The right type of concrete for foundations
Choosing the right concrete mix for your foundations is vital. Lesser strength concrete is usually cheaper, but it’s important to choose the right mix that offers the correct strength to support the building above it. The different types of concrete are made using different ratios of cement, sand and water, and different types of aggregates.
Often a mix of C25 is sufficient for smaller build foundations, but the larger the project the higher the compressive strength required. Have a look over the different types of concrete available, or simply give the expert team at All Mix Concrete a call to discuss your project, and we’ll be happy to advise you.
The depth of concrete foundations
Foundations are made by digging down into the ground. The required depth is often dependent on the type of earth you’re building up on. For example:
- If your soil is very heavy with limestone, granite, sandstone or hard chalk, this rock material will provide some support to your build, so it is likely you can build more shallow foundations.
- If the soil is very soft with chalk or damp clay, all of this material will need to be excavated until you reach a firmer ground below.
- If the soil contains large amounts of gravel or sand naturally, this can lead to the strength of the foundations. However it must be properly compacted to avoid the foundations collapsing.
- If the soil is mainly peat or very loose and sandy, it will not bear load well. You will probably have to build a solid raft foundation, to prevent sinking.
Often, if you need to dig down further than 2 meters, or 6 feet, you will have to build additional support within the foundations system to stop the trenches collapsing in. As a result, it’s generally more cost effective to build a reinforced concrete raft for your foundation system.
The cost of concrete foundations
The cost of building your foundations will depend on a lot of things, not just the quantity and compressive strength of your concrete.
- Large scale excavation may require the hiring of specialist excavating equipment.
- You may need to pay for the disposing of the excavated ground
- You may need to buy damp proofing membrane, reinforcing materials and the wooden formwork
- Concrete pump hire may be required to get the concrete to the required location
- And finally, the cost of the concrete and delivery
Pouring concrete for foundations
You will need to carefully plan how you’re going to pour your concrete, to create the most supportive foundation system. A few things to consider are:
Mono pouring is very commonplace and offers a range of benefits. It simply means that the frame for the foundations is built with no joins or breaks. This allows the concrete to be poured into the entire structure in one go, creating a stronger base and no joints that need waterproofing. This may sound straightforward if you’re constructing a small garage, but if the build is complicated, it may mean planning the formwork carefully to avoid joins.
If the site has easy vehicle access, you could pour the concrete straight from the lorry chute into your framework. However if the site is set back, you may need to wheelbarrow your concrete from the lorry to the site. This is less effective as it is difficult to achieve even distribution of the concrete, especially if using the mono-pour method. It’s also messier, slower and requires more manpower.
The other option to consider is hiring a concrete pump. This uses a series of connected pipes that transport the concrete from the lorry to the foundations.
The concrete needs to be raked into the framework evenly, so being able to move the chute or pump back and forth over the structure, while it is raked is vital so be sure you have enough tools and people on site to help.
If your concrete pour is planned well, and carried out effectively, you will find it much easier to level the concrete. A level foundation is key to level build, as correcting an uneven foundation with the construction can be tricky.
Avoid trench collapse
Finally, be sure to keep an eye on the form work as you pour and rake, and respond quickly to secure the frame if it begins to move. If you don’t notice the framework is unstable, it could collapse during the pour, resulting in a significant cost and delay to your project.
When can I build on my foundations?
Allowing your concrete sufficient time to cure (set) is essential. The curing process is actually continual, so your concrete will continue to strengthen for years to come. However, the compressive strength of your concrete is graded after 28 days. So, although you may be able to walk on your concrete after just a few days, if you need a specific strength of concrete for yoru build, it’s best to wait 28 days for it to reach that necessary strength.
If you need your concrete to cure sooner, you can mix accelerator additives into the batch. This is an additional cost, and may not be the best option for your construction project. If you’re unsure, speak to your concrete supplier and follow their recommendation. Don’t be tempted to start construction too soon, as your final build will not have the strength and support it needs.
All Mix Concrete
The team here at All Mix Concrete are on hand to provide expert advice for your building project. So no matter what you’re building, you can rely on our team to help. Get in touch today to find out more.