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Concrete floor in new extension....help!



 
 
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  #1  
Old May 22nd 05, 10:18 AM
Junior Member
 
First recorded activity by DIYBanter: May 2005
Location: Bournemouth
Posts: 3
Default Concrete floor in new extension....help!

I have just built a single storey kitchen extension with a 150mm reinforced concrete oversite base. The building regs required me to install a DPM under the slab and another (more substantial) dpm layer on top of the slab prior to laying 60mm of insulation and an 60mm screed.

The central heating pipework will be laid in the screed. When testing 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 i put the screed down? I have exposed part of the slab by removing the insulation and peeling back the upper dpm and this has slowly dried over the week but the dpm is keeping the wet in where its still covering.

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

Thanks.
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  #2  
Old May 23rd 05, 12:21 AM
The Natural Philosopher
external usenet poster
 
Posts: n/a
Default

scudder wrote:

I have just built a single storey kitchen extension with a 150mm
reinforced concrete oversite base. The building regs required me to
install a DPM under the slab and another (more substantial) dpm layer
on top of the slab prior to laying 60mm of insulation and an 60mm
screed.


I am surprised at the lower DPM.


The central heating pipework will be laid in the screed. When testing
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.


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.



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


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.


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


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.



Thanks.


  #3  
Old May 23rd 05, 07:38 AM
Junior Member
 
First recorded activity by DIYBanter: May 2005
Location: Bournemouth
Posts: 3
Smile

Quote:
Originally Posted by The Natural Philosopher
scudder wrote:

I have just built a single storey kitchen extension with a 150mm
reinforced concrete oversite base. The building regs required me to
install a DPM under the slab and another (more substantial) dpm layer
on top of the slab prior to laying 60mm of insulation and an 60mm
screed.


I am surprised at the lower DPM.


The central heating pipework will be laid in the screed. When testing
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.


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.



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


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.


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


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.



Thanks.

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

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

Maybe I'm being paranoid ....any other comments welcome!
  #4  
Old May 23rd 05, 02:17 PM
The Natural Philosopher
external usenet poster
 
Posts: n/a
Default

scudder wrote:



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


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

I understand that the slab is in contact with the 'wet' ground in other
projects - looking at BS8023/8024 seems to confirm this. I suppose
logically water shouldn't damage the concrete (provided its mixed
correctly) but still wonder about the A193 mesh reinforcement.


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
the confined moisture might cause mould, humidity and/or smell if it
leaches out through the inevitable gaps where the upper dpm meets the
dpc in the wall.


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.


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


  #5  
Old May 23rd 05, 06:26 PM
Junior Member
 
First recorded activity by DIYBanter: May 2005
Location: Bournemouth
Posts: 3
Default

Quote:
Originally Posted by The Natural Philosopher
scudder wrote:



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


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

I understand that the slab is in contact with the 'wet' ground in other
projects - looking at BS8023/8024 seems to confirm this. I suppose
logically water shouldn't damage the concrete (provided its mixed
correctly) but still wonder about the A193 mesh reinforcement.


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
the confined moisture might cause mould, humidity and/or smell if it
leaches out through the inevitable gaps where the upper dpm meets the
dpc in the wall.


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.


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

Thank you, that info is very much appreciated.
 




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