Concrete floor in new extension....help!

[scudder]

I have just built a single storey kitchen extension with a 150m

reinforced concrete oversite base. The building regs required me t install a DPM under the slab and another (more substantial) dpm laye on top of the slab prior to laying 60mm of insulation and an 60m screed.

The central heating pipework will be laid in the screed. When testin the pipework, I had a dry joint in one of the pipes and had a flood!! The water got under the DPM and wet the slab and blinding layer.

Can anyone advise me if this needs to be completely dried out before put the screed down? I have exposed part of the slab by removing th insulation and peeling back the upper dpm and this has slowly drie over the week but the dpm is keeping the wet in where its stil covering.

If i lay the screed next week, this moisture will be sealed in by a dp layer above and below the 6" slab, will it cause damage to the concret or reiforcement?

Thanks

-- scudder

[The Natural Philosopher]

I am surprised at the lower DPM.

I hope you are not laying copper directly in the screed...you shpould only use plastic in the concrtet directly: Copper must be laid in cojndut or possibly in some sort of faom insulation type layer to keep cement and copper apart, and allow for differential expansin.

Anyway if it got under the DPM to the bit thats in contact with the ground, forget about it., Ground is the wet side anyway.

I am completely puzzled as to what you have. Why two DPMS for example.

If youi ar about to spla down screed that is full of water, a bit more seems to me to be irrelevant.

No. Water does not hurt coincrete, but again, I have NEVER seen a floor laid like this. Noprmally the slab goes onto the earth, then its blinded DPM'ed insulated and screeded in that order.

Copper pipes are NEVER laid in the screed, as your BCO will inform you. For reasons you have discovered already.

[scudder]

Thanks for this. The position and guage of the dpms was put in the spe at the request of the BCO so I'm puzzled now too. Its the second projec I've done like this. The pipes are insulated and layed in accordanc with the heating engineers advice/spec.

I understand that the slab is in contact with the 'wet' ground in othe projects - looking at BS8023/8024 seems to confirm this. I suppos logically water shouldn't damage the concrete (provided its mixe correctly) but still wonder about the A193 mesh reinforcement. Also, i the confined moisture might cause mould, humidity and/or smell if i leaches out through the inevitable gaps where the upper dpm meets th dpc in the wall.

Maybe I'm being paranoid ....any other comments welcome

-- scudder

[The Natural Philosopher]

Oh well. As long as you know what you may be in for.

Concrete works as well under water as above it. Steel ereinforciong mesh hepls prvent buckling and cracking. It won;t rust either - needs air as well as water. As long as cement rartio is high enough the concrete is relatively iompervioaus to aoir AND water both.

Screed however, mixed with less cement is full of holes. Screed can and does absorb water and needs tio be above teh last DPM.

Also, if

No...inevitably there is always a gap in the DPM one way or another, but as long as the rate of drying exceeds the capacity of the underlying to generate moisture you are OK and mould won't form. You need a bit of air for most moulds as well, you know.

DPM is not an absolute thing - its more about keeping the relative humidity of evertything below the critical 100% at which actual water forms, or if it does, making sure is where it doesn't matter. Like under a DPM.

[scudder]

Thank you, that info is very much appreciated

-- scudder