Hardcore base for floor slab ..... or not?

[^woody^]

This is the job - a 3.5m x 3.5m conservatory floor slab (the wall foundations are built).

It will be 50mm screed, 100mm concrete and 80mm celotex insulation ... but I don't know whether to bother with hardcore.

Previously the area was block paved on at least 50mm whacked sand, and this was on firm ground (no top soil). The paving had not moved in ten years since it was laid.

If I remove the pavers and scrap the sand, then its just the right level for laying the insualtion and blinding, so I wondered whether to bother removing 100mm of this soil for hardcore?

My thinking is ... the ground is well compacted, it has not moved for years, the insualtion boards will spread some load/take some minor movement, and the floor slab itself will exert an even load.

I can't see a reason for the hardcore, nor for any significant movement

So hardcore, or not?

(BTW, its not the cost of a few tonne of H/c, but the time and disposal of the soil that is the issue)

 

[stuart45]

If the ground is rock solid then I wouldn't use hardcore. I have built floors on solid chalk without it, and there has been no problems 30 years on. Hardcore does settle slightly, so the ground may be better.

 

[Deluks]

Maybe a couple of sheets of A142 for good luck?

 

[noseall]

Provided the ground is not unfeasibly wet and prone to any shrinkage then why not let this one go. I take it there is no 'dark' matter down there?

 

[^woody^]

When digging the footings by hand, the ground was 7.6 on the blister scale.

I just don't think what would come out would be any less dense than the hardcore that went back in.

 

[Thermo]

id go with your assesment, cant see the point

 

[noseall]

I just don't think what would come out would be any less dense than the hardcore that went back in.

I have been prepping my drive recently in readiness for the 'mackers to come and spread their stuff.

The ground local to me is superb building ground - compact sand and gravel. Luvverly. When the eight wheeler, loaded with 16.5 tonnes of mot, backed onto the subsoil, it hardly budged. A delivery truck made a greater impression in the mot when dropping a couple of tonne of sand!