Replacing brick shed concrete floor

14 Jun 2010
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United Kingdom
I have a 5m x 3m brick shed that I'm in the process of upgrading, and would like some advice on replacing the concrete slab floor, which has several cracks in it and lets in the damp. The slab is separate and inside the walls, ie, the walls are not built on the slab. The walls have a DPC 2 brick rows above the slab, I'm guessing the slab did not have a DPM from the fact that damp is coming up.

I'd like to upgrade the floor, as far as I can see my options are as follows, in ascending order of ease / complexity:

1. Simply put a membrane on the existing floor and pour 4" of concrete on top of the existing slab. The shed will only be used as a pottery so not have to take heavy or industrial use. New floor level will still be below DPC in walls.

2. Break up existing slab, lay membrane on what's exposed and pour 6" of concrete in. If I do this, would I need to put sub-base of type 1 or similar down first?

3. As above but dig out and put down hardcore plus sub-base, then membrane then concrete.

The lasts sounds like overkill to me. 1 is easiest but I'm not sure about just laying one slab on top of another. With all these options are there any real benefits to putting down insulation board under the concrete? The shed is only single skinned and not heated, so will never be something you want to spend a lot of time in during the winter.

Any thoughts / comments welcome..


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No 1

It's an unheated shed and your original concrete although cracked will have settled to a degree by now and isn't a bad base to start with.
Thanks both - looks like the easy option it is! :D Is 4" about the right amount of depth required?

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If you are using all in ballast at 1 to 6, you will get away with 80mm thickness.
By the way, nice to see someone say thank you.
old un. :D
You're welcome - when answers come as fast as they seem to, it would be rude not to be grateful..

I have a follow up question relating to lating a slab - not having done one before. In this case it will be 5m x 3m, and I'll get in ReadyMix - there's a company locally that can supply small loads. Question - with this size, should I try and lay it all one go, or use shuttering and break it into smaller blocks - say 3m x 1.5m?

If it's all in one go - is it best to spread it out, then wade around in the wet mix, tamping and levelling as you work backwards towards the door?

If it's in blocks, then do you remove the shuttering just before you lay an adjacent block, or leave it in and remove it after you've laid both blocks and fill in the hole thats left behind? (Hope that makes sense - bit hard to describe..)

If anyone has any pointers to a guid for doing this would be much appreciated!



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