extension floor/slab cock up??

[higgster]

Hi,

I have possibly cocked up my extension slab, here are the details.

My floor construction is as follows,

40mm rejects infill around footings, 150mm MOT type 1, sand blinding, DPM, 100mm Celotex, DPM, 150mm concrete.

The reason for the second DPM above Celotex is the building inspector said, 'you cant lay concrete on top of the Celotex, just put another sheet of DPM across and concrete over that'.
Without thinking to much thats what I did.
Fast forward 8 odd weeks (whilst building a garage) I have now come to put the walls up on the extension.

I have noticed the following, the layer of Celotex sandwiched inbetween the two DPM's has filled with water!!!!

I have punctured a couple of holes around the edge of the lower DPM allowing the water to drain out. This still mantains the integrity of the DPM below the concrete.

My question is, is this OK or am I going to have to break up the slab and start over, due to not knowing how 'wet' the celotex is. I appreciate wet Celotex loses its efficiency.

Really don't want to break up the concrete and re-lay it, but also dont want any damp issues either.

Any help/suggestions greatly appreciated.

 

[mointainwalker]

The ability for Celotex to absorb water - even when immersed - is minute: something less than 0.01% by weight over 30 days if I recall correctly.

The amount is so small that I wouldn't spend a moment worrying.

 

[higgster]

Thanks for your reply,

The thing I was thinking is, even though I managed to puncture a couple of holes and allow the water to drain out, it is still going to be relatively damp.
It won't be able to dry out so is it OK leaving it like that? I am probably over worrying but would hate to have to dig the floor up in a couple of years time due to damp/mould etc etc.

As long as the DPM directly under the concrete hasn't been compromised and I tie it in correctly with the DPC then it should be OK???

Cheers

 

[theoldun]

Extracts from Celotex Technical Sheet.

Moisture Resistance
Water absorption through exposure to moisture or indeed in exceptional circumstances through floods, is a significant factor in the selection of any modern insulation. The thermal performance of mineral wools and phenolic foams is significantly compromised and reduced when exposed to water. Celotex due to having a closed cell structure is a hydrophobic product meaning it does not absorb water. This allows the thermal performance and integrity of the product to be retained over time.

Life Expectancy
As Celotex products do not sag, absorb moisture or be permeated by air, you can be confident of consistent performance which will typically last the full lifetime of the building. There is also no requirement for additional maintenance or treatment to the Celotex boards during this time.
oldun

 

[Nige F]

Life Expectancy
As Celotex products do not sag, oldun

shame the same doesn`t apply to our bodies

 

[higgster]

OK so the celotex is going to be OK, what about that damp trapped beneath the two layers of DPM?

Is that OK? Is it just like the ground being damp underneath the floor construction, it doesn't matter thats why you have a DPM?

Im trying not to loose sleep over this but obviously not being a pro I do get a bit worried.

And it's holding up my progress a little!

Thanks again for the replies, It is always good to have a little re-assurance.

 

[simonjay]

OK so the celotex is going to be OK, what about that damp trapped beneath the two layers of DPM?

Is that OK? Is it just like the ground being damp underneath the floor construction, it doesn't matter thats why you have a DPM?

Im trying not to loose sleep over this but obviously not being a pro I do get a bit worried.

And it's holding up my progress a little!

Thanks again for the replies, It is always good to have a little re-assurance.

If you had (not cowboy) builders in doing the work, they'd not give it a moments thought. Lots of builds get saturated before the roof is on. They always dry out in the end somehow.
This happened during my build and I've have no problems. Its possible to think too much !
Simon.

 

[Adam Smith]

Hi Higgster,

I have stumbled across this topic as I have a similar concern. Currently self building an extension and floor make up is 150type1, sand, DPM 1200, 125mm celotex, DPM 500.

We Are pouring 100mm concrete (steel set up with underfloor heating) on the weekend. It has been raining recently and have noticed water laying between the two DPMs where the celotex sits.

6 years on is your extension ok or are you having damp problems?

Kind Regards
Adam

 

[freddiemercurystwin]

Do you think it's likely that the OP will reply given that his last post was in 2011?