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I am building a 6ft x 4ft garden shed which will have a concrete base.

I've levelled some ground, built a frame, and made a floor out of old bricks.

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The ground is fairly clay-heavy. I've been stamping down on the bricks and they seem stable. Cement will be about 6-9cm from the top of the bricks to the top of the frame. There is a few millimetres of gap between the bricks, I imagine the cement will not flow between them and hence it will be kept clear of pooling water. The bricks are partially above and partially below the level of the surrounding soil.

I haven't worked with cement before but based on what I've read I believe this will work.

Can you see any problems? Is there anything missing? Do I still need grit? Rebar? Or is it okay to just go ahead and pour?

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    The trouble with that sort of base is that it creates specific stress lines. If your slab cracks, it'll almost certainly crack along those joints. You're better off with something more fluid, like gravel.
    – isherwood
    Mar 16, 2021 at 19:37
  • That said, I don't have experience pouring concrete on rigid bases.
    – isherwood
    Mar 16, 2021 at 19:42
  • How cold is in the winter? You might find your slab has settled unevenly and cracked in the next weather cycle. If digging is too much for you, you shall at least add rebars, or wire mesh, to make the concrete slab stronger, and less prone to crack.
    – r13
    Mar 16, 2021 at 21:59
  • I just put brick on level ground and that has been the floor for 20 years. Insulated shed so no freeze/ thaw. Water spills drain very well.
    – blacksmith37
    Aug 13, 2021 at 23:17

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Concrete slabs perform best when it has a uniform thickness, installed on uniform compacted soil, square (or near square) in shape (not “L” shaped), and has temperature reinforcing steel if the slab will expand or contract too much due to changing weather, roof loads transferred to perimeter.

Your building use will probably require large loads of fertilizers, water bins, etc. that will impose significant loads that will cause differential settlement. Using a brick base will add to the possibility of cracking by making the slab an uneven thickness, non-uniform depth at various locations, etc.

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I’m no expert but it looks like you’ve made a good job for your shed base and will be more than substantial for a 6x4 shed. When you talk about ‘cement’ you mean concrete? So that’s cement with aggregate in for strength. If the wooden surround is level from side to side, once filled you’ll be able to strickle across to produce a smooth and level surface (or sloping fractionally for drainage?). Regardless of the underling surface the shed should go onto a slight wooden frame (use tanilised wood) to raise it slightly to avoid the base of the shed from rotting. Once your concrete base is finished and the surrounding ground levelled (or whatever you intend doing with it), see how the water drains and this will determine the height the shed needs to be raised. Usually this is only 2-3cm. Good Luck!

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  • Missing appears to be a much deeper hole layered with gravel and sand. That's my understanding of how to form the base. This is, however, not my forte.
    – DAS
    Apr 16, 2021 at 8:15

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