Concreting over slabs

[Aldo's Dad]

Evening everybody,

I am having a new shed built (16' x 8').

The slabs that I was going to lay it on are not level enough for the shed. I have been advised that I should take them up and relay them all on a sand base.

I was wondering if it may be quicker to do a concrete base (100mm) on top on the slabs, as time is of the essence.

I have calculated I will need just over 1.4 cubic metres of concrete.

Two questions: Is it a reasonable idea and any idea how much it would cost?

Cheers

Aldo's Dad

[lutonlagerlout]

well aldos dad
you need to excavate 100 mm
shutter the area with some 100mm by 18 mm tanalised path edging
then pour the concrete
and tamp to level
1.4m3 will probably cost you about £170 from a mini-mix concrete company
this is approximately 32 full barrows of concrete
plus you need somewhere to put the earth you dig out
so if i was doing it as a pro job it would cost around £600
if you DIY it it would cost about £200-ish
slabs will probably be cheaper but laid on sand will fail in time
hope this helps
cheers LLL

[Aldo's Dad]

Thanks for that LLL.

The slabs are already down and it is the slabs that are not level enough for the base of the shed.

What I was wondering was can I put the shuttering around the slabs and lay the concrete directly on top of them?

Cheers

Aldo's Dad

[Rich H]

If the slabs are not level it's probably because they are not on a solid base. If you concrete over them it's likely to crack in time. You could lift them and smash them into hardcore thereby reducing the volume of the concrete required (3 tonnes according to your volume calculation) and removing the concern over future instability. The quickest and cheapest way though would be to lift the slabs and relay them on a sharp sand & cement mix. Plenty solid enough and will save both money and time.

[lutonlagerlout]

^^
LLL :;):