Help: concrete slab foundation surface cracks - I have surface cracks is this a problem?

[barnsley boy]

I'm rather wrooied and would really appreciate some info/feedback.

Whilst I was away my buildrers poured a concrete slab, 3.5 x 6m and between .3 and .6m deep was poured, in hot sunny conditions (last friday). It was a slab as the ground is made up. Re-bar mesh was also used. Some hardcore was compacted on half of hole, but the remainder was made up earth and for reasons I can't fathom the visqueen (?) plastic sheet has not been used.

The surface has a number of cracks none more than 2mm wide, most less. On one I tested in photo i could insert a small piece if wire 50mm into crack. Most cracks will be internal to structure bit some might be where bricks will be laid.

Do I have a problem?
Is there any remedial works that is needed or would help?

Many thanks for any assistance. I have a pohto if thishelps but can't see any way to attach (150kb)

BB

[Rick]

You should not have any cracks in a reinforced raft foundation. Cracks would allow water ingress, which would cause rust on reinforcement and possibly failure.

There should have been full sub-base rolled or vibrated in, and if for a habitable construction then a DPM should have been installed.

Is this under Building Regs ? ... is so explain the issue to the building inspector, if he condemns it then you have a case for getting your builder to take it out and start again at his cost ... your key clause ... is the job 'fit for purpose'

If not then the supplier is liable.

[barnsley boy]

Rick,

Thanks for the reply. The slab foundation is for a conservatory and therefore BC are not involvewd (unless they need to be).

The depth of concrete is between 300mm (in centre) and 600mm (edge). The centre had a layer of crushed aggregate. Most of the base will be covered as above it will be block and eventually post and beam (pot and beam) floor. I was concerned that where a crack starts at a piece of shuttering and runs under the block work the effects of water freezing in winter might cause cracks to increase.

Is this an issue?

BB

[Rick]

IMHO ... I would not want to see a crack (of type you describe) in a floor that is attached to my house ... if they did not install a DPM, how are they intending to prevent damp ? presumably they have a plan for this ?

That may help you to decide whetrher this is acceptable or not .... in any event it should be filled, there are 2-part epoxy loaded cement grouts made particularly for filling cracks .. a quick Google should find them (same firms make self Levving compounds) ... you could treat cracks with this.

[barnsley boy]

Thanks Rick, we seem to have reached the same conclusion as you. The slab is a foundation onto which blocks and brick will be built up (with dpc as per main house) for the conservatory dwarf wall. My concern was the integrity of the slab, especially considering repeated annual winter freeze/thaws. We too have concluded that filling the cracks to prevent water ingress is the best course of action.

Thanks for your help.

BB