depth of foundations

[MrPlank]

Hi Guys

I am laying a concrete slab in garden for a timber outbuilding the dimensions of the slab are to be 7 metres x 4 metres. my understanding is that I need to have a depth of hardcore then DPM then wire mesh and then concrete. My question is how deep should the hardcore layer be and how deep should the concrete be. Also do I need a particular size for the wire mesh. Thanks for any help

 

[John D v2.0]

I'm not a builder but I'd say 100-150mm hardcore on un disturbed subsoil, half an inch of sand, dpc and then 100mm concrete.
You wouldn't put mesh directly on the dpc it would damage it. If you do need mesh for crack prevention due to the large slab it would be A142 or similar and be in the centre of the concrete

 

[bobasd]

yeah, A142 comes in 6mm thickness and will do fine.
use A142 with mesh chairs/spacer supports.
the oversite earth should be whacked down so should, as above, 100 to 150mm of any stone hardcore.
use min of 25mm sand
the dpm droops over the shuttering boards.
pump the conc.

 

[John D v2.0]

Interesting thanks, as i say I'm not a builder i was just going by nhbc which say use the minimum blinding to cover the hardcore but you're right the usual spec is an inch or two. On our drive we only used the bare minimum.
See blinding on this URL
http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2006/Part5/section1/sitework.htm

 

[^woody^]

If it's a foundation then you dont want to be putting it on hardcore. If it's a floor, then its OK.

 

[MrPlank]

Hi guys

Thanks very much for the advice its very much appreciated.