How To Build A Concrete Base For Your Shed (2024)

Finishing a concrete slab

If you’re building a shed, or other structure in your garden, such as a greenhouse, summer house or even an office, you’ll need to give it a sturdy and strong concrete base that will support the structure, provide a level base and protect it from rot as a result of groundwater seeping in.

If you’re used to undertaking DIY projects yourself, you can easily build your own concrete shed base in just a day or two. Follow our simple guide below to get your concrete slab poured and finished properly.

You might be tempted to just pour your concrete into the formwork and leave it, especially if you have a self leveling compound, but for the best results follow our steps below to ensure a smooth, level and long lasting finish.

Tools you’ll need:

Wooden frame or formwork
A long straight plank or wood
A long handled concrete bull float
A short handled hand float
A concrete edging tool
A trowel or stiff broom

Stage One:

Once your concrete has been poured into the formwork, simply take your plank of wood and drag it across the surface of the concrete in a sawing, back and forth motion, to scrape the excess concrete from the surface. The plank of wood should be able to reach across the slab of concrete and rest on either side of the formwork. It’s handy to have a helper at this stage so you can each hold an end of the plank of wood while sawing across the concrete. Start at one side and work across to the other side. This will collect any overflow concrete as you go and when you reach the far side you can remove the excess and dispose of it.

Stage Two:

Now you can take your bull float (a smooth flat surface, mounted on the end of a long handle) and smooth over the whole concrete surface. If you hold the bull float at a slight angle, and press gently into the surface, it will even out any rough bits.

Stage Three:

Next up, take your concrete edging tool (a small, flat surface with a rounded edge) and run it along the sides of the concrete slab to smooth over the edges and corners.

Stage Four:

Now it’s time to cut control joints in the slab to avoid cracks as it cures. Control joints are simply lines cut into the surface. The lines should be about a quarter depth of the thickness of the slab, so far an 8 inch slab, the controls joints should be 2 inches deep. The lines can be made with the edge of your bull float, and should be cut in evenly across the whole surface. Pay particular attention to areas that are most susceptible to cracks, such as narrow areas and inside corners.

Stage Five:

The next step is to wait for the bleed water to evaporate. It is a normal part of the curing (setting) process and is simply excess water leaving the concrete as the curing begins. Evaporation will be quicker in the hotter months, than in the winter months, but it’s important not to rush ahead until it has finished.

Stage Six:

Now take your hand float, which is like a bull flat but on a smaller handle, and smooth over the entire area again. Again hold the float at a slight angle to graze the surface and even out any rough bits.

Stage Seven:

The final step is to finish the concrete. Depending on the use of the base, you could opt to finish the concrete with a stiff bristled broom to add texture that will stop it getting slippy in wet conditions. Your other option is to create an entirely smooth surface, which is easier to keep clean in internal applications. For a smooth finish, use a trowel instead.

The Curing Stage

Now it’s simply a matter of waiting for the concrete to set. The setting process is actually called curing and is a chemical reaction that results in the wet concrete becoming hard. This process is continual and so your concrete will actually continue to harden and build strength for years to come. All concrete will reach its optimal strength after 28 days, so it’s best to wait a full month before building on your slab.

However, if you speak to your concrete supplier, they will likely advise you that you can walk on your concrete after a few days.

The curing process happens naturally and begins as soon as the concrete is poured into place, which is why it’s important to familiarise yourself with the above steps so you can get the slab leveled, smoothed and finished as quickly as possible.

Protecting Your Concrete

It’s important because your concrete retains its integral moisture for the chemical process to work. If it’s a hot day, it might dry out before the concrete has properly cured. Similarly, if the concrete gets too wet, if it’s raining for example, the excess moisture might also affect the curing process. To avoid either of these scenarios, you might need to cover your concrete with a polythene sheet while it cures.

If you’re pouring concrete in very cold temperatures, you might also need to take additional steps to ensure optimal curing. Read more about that here: Cold Weather Concrete Pouring

It’s always best to check with your supplier to make sure you handle your concrete correctly. They’re the experts and will be able to advise you if you think you need to cover or protect your slab, and will let you know the optimal waiting times before you begin to build on it.

King Concrete

Here at King Concrete, we offer an expert concrete supply service, with reliable deliveries and professional advice to help you get the best finish. We can provide ready mixed concrete or mix up your concrete on site, depending on your requirements, and we also offer a range of additional services including borrowing and pumping to help you get the concrete into place quickly and with no mess or hassle.