How to lay a concrete shed base
Concrete is prized for its durability and adaptability, from setting up a simple backyard shed to laying the foundations of a sprawling industrial complex, the choice of concrete plays a pivotal role in the longevity and success of any project.
In this guide, we will delve into the essential steps and considerations for laying a concrete shed base, a fundamental task for securing the stability of your outdoor structure. Following a detailed, step-by-step guide will help ensure your shed base is robust, level, and durable.
How to lay a shed base
Concrete is perfect for creating a solid, hard-wearing base for your garden shed. The first step is to mark out the area where the concrete will be laid, adding an extra 100mm to the width and length of the finished shed to allow a small edge around the base. Also, a further 75mm all-around will be added to accommodate the timber formwork, which will hold the fresh concrete in place while hardening. The easiest way to mark the area is with a string line and stakes, ensuring the corners are at right angles.
The concrete base should be at least 75mm thick, with a similar layer of sub base, so you will need to excavate to the required depth and ensure that all plants, stones and debris are removed before compacting the ground with a roller or tamper.
Are you looking to lay a concrete base? Our guide provides further expert tips.
Building formwork for the concrete shed base
The formwork is constructed using 25mm timber planks, and it must be level, as this will determine whether your finished concrete slab is level. Additional pegs should be placed at 1-metre intervals around the outside of the formwork to provide extra support when the concrete is poured.
Then, 75-100mm of hardcore is added, and it is compacted before adding a layer of building sand to protect the damp-proof membrane. If there are any joints in the membrane, these should be overlapped and taped, and the edges should be turned up against the formwork to form a tray. Be as accurate as possible with your levels as a deviation of as little as 1cm over a 25m2 area will increase the volume of concrete you require by ¼ of a cubic metre (Over half a tonne).
Concrete needs to be poured and levelled quite quickly as it begins to ‘go off’ (harden) within two hours of being mixed, so you will need to make sure everything is ready before the concrete delivery truck arrives. Calculate the volume of concrete you need (length of concrete slab x width x depth) and make sure you order a concrete pump if your site is hard to reach or the volume of concrete is too large to place by wheelbarrow.
Use our concrete volume calculator
Concrete mix for shed base
If you choose to mix your own concrete, a standard concrete mix ratio of 1 part cement to 5 parts ballast (aggregate and sand) is usually perfectly adequate for shed bases, but you can add reinforcing fibres if you are housing something particularly heavy. If you need more clarification or would prefer to receive your concrete ready-mixed in a truck, ask your ready-mixed concrete supplier for advice.
You must wear the correct safety clothing (long sleeves and trousers, gloves, rubber boots and safety goggles), as concrete is caustic and can cause serious injury if it comes in contact with skin or eyes.
Learn more about the safety precautions you should take here.
Laying a concrete shed base
Begin pouring the concrete into the furthest corner of the formwork and using a rake or shovel to spread it evenly. Ensure it is around 10mm higher than the formwork to allow it to be compacted and remove any air pockets.
This is a two-person job and requires the use of a straight piece of timber longer than the width of your formwork. With one person at either end, the timber can compact the concrete and level it in line with the top of the formwork by performing a sawing motion. Ensure there are no low spots and the corners are filled before running a trowel along the sides of the formwork to smooth the edges and reduce the chances of it chipping.
For more information on how to prepare for a concrete pour, read our guide.
The concrete mustn’t dry out too quickly, so if the temperature is likely to reach 20°C or above, use plastic sheeting to cover the slab for at least 24 hours. The concrete can be walked on within 48 hours, but ideally, the formwork should remain in place for at least five days before removing it and building the new shed.
For further information and expert advice, explore our ready-mixed concrete page or speak to our team today.
