Groundwork & Foundations

small slab at front of house

Anonymous user 28/02/2024 - 3.50 PM

Hi everyone, I am planning a small extension, 1800mm x 800mm. There is currently block paving there at the moment sitting on sand and darbo which has been there around 15 years, its pretty solid. Can I pour concrete for the slab on top of the blocks, (I need to come up about 130mm from the top of the blocks), if I use a membrane of course. There will be 2 timber frame walls to go on top of this at a height of 2000mm. Thanks in advance, Gary

Anonymous user

I take it some kind of footing&foundation has already been done? I would lift them take out the sand and break the blocks up to us as hard core for a good soild base then pour your slab if not it could possibly drop after time and form cracks

Answered8 July 2020

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Anonymous user

No you can’t you can’t put any load bearing on sand

Answered8 July 2020

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Livingston

You would be better lifting mono blocks and excavate down to a hard level should be 450mm below ground for frost cover . Build back up to that level then put your concrete slab to you level required . Putting in a membrane layer and reinforced concrete If you are going to do a job you are better doing it well . And not cutting corners it mite look solid . But is it worth taking the chance ? Hope this helps

Answered3 August 2020

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Anonymous user

If you only have 130 clearance from damp to block paving I would rip all paving out place to the side also with the sand, you will also have to dig down further as you'll need to allow at least 100mm sub base (smashed up block paving) 50mm blinking you can use the sharp sand or building sand dosent matter 100mm concrete, 100mm celotex and 60mm screed. I hope this helps

Answered3 August 2020

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