Dear Users, our volume builder will pour the concrete slab on Monday (today being Saturday). I am now concerned that the heavy rainfall experienced during the prep-work this week may have lead to sub-standard work.

By way of background: a) Two days ago, as I walked the roadbase pad (with a minimum load bearing capacity of 50kPa), my boots were sinking up to 15cm at worst in some parts. b) Yesterday the membrane, waffle pods and steel were done.

Should I be concerned that several of the pods are unstable when stepped on? Two of which have visible gaps with the plastic of at least 10cm (hence the rocking when stepped on). I was unable to arrange an inspection this weekend and am unsure how the builder would react to an intrusion on Monday. Any advice would be greatly appreciated.

Hi dh3121 this is probably too late but may help your concerns.

50kPa bearing capacity is very soft soil, as an example a 60kg person would exert about 40kPa (assuming a 50mm x 300mm foot) directly beneath their feet. This should be enough to sink into the soil. The waffle pad slab helps to distribute this load once it is poured.

Ideally the polystyrene should be well restrained and should not move too much. One concern with this form of construction is the styrene moving and the thickness of the concrete above becomes questionable. If the contractor is experienced in this type of slab then thing should go OK, their only issue is if the gaps are too big they may need more concrete.

If you have any concerns contact the builder, you are the client, they are the experts. If they can not satisfy you that they are doing the right things then get a second opinion. Do not hesitate to stop the work if you aren't satisfied. You are the client, you are paying, if they can't prove that they have done the right thing then don't pay. Take things slowly and never let them rush you, it will save your peace of mind but not necessarily your patience.

Good luck and I am sure that things went well.