# Concrete floors poured in rain?



## Cyrstal (22 Sep 2011)

Hi All,

I have a query.  We are building a house at the moment, and the builder poured the concrete floors yesterday even though there were downpours all day??  Is this normal? The concrete was poured over underfloor heating that had been placed over insulation on Monday...

I am worried as I thought you had to have dry weather for pouring concrete?

Thanks,
C


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## Docarch (22 Sep 2011)

I don't mean to frighten you but the pouring of the concrete in rain will result in an increased water content and lead to slightly reduced strength and an increased risk of shrinkage of the slab (although if there is reinforcement in the slab this will reduce the risk of shrinkage).  Generally not a great idea to pour concrete in the rain.  

Do you have a structural engineer involved in the project?  Really you should consult him/her about the matter.


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## onq (27 Sep 2011)

Hi Crystal,

+1 what Docarch has posted and I note the following

Here is [broken link removed] which attempts to explain several of the known issues arising.
I would consult with an Irish engineer in relation to testing and remedying any defects that might be discovered.

If this is a shallow concrete slab proportionally more concrete will be affected, with surface issues arising
If yours is a deep raft construction with structural issues arising this must considered by an engineer.

One issue the Aussies don't cover very well is the effect that saturated ground can have.
Not something you'll find down there, but pouring onto saturated ground is a risk here.

Do NOT accept the builders advice on this slab even it if ruins your relationship.
Unless he has taken the necessary precautions he may be taking it out.

Take professional advice.


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                               as a defence or support - in and of itself  -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                               Real Life with rights to inspect and issue        reports    on     the         matters    at      hand.


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## sse (27 Sep 2011)

Cyrstal said:


> Hi All,
> 
> I have a query.  We are building a house at the moment, and the builder poured the concrete floors yesterday even though there were downpours all day??  Is this normal? The concrete was poured over underfloor heating that had been placed over insulation on Monday...
> 
> ...



Is this stage the screed over the underfloor heating being poured in a "watertight" house, i.e. does it have walls and a roof, or is this the initial floor slab?

SSE


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## hastalavista (27 Sep 2011)

sse said:


> Is this stage the screed over the underfloor heating being poured in a "watertight" house, i.e. does it have walls and a roof, or is this the initial floor slab?
> 
> SSE


Sunny South East: From the OP's post it says its a slab over the UFH

I would imagine that the builder decided to do this before any walls as its much easier, just pour and powerfloat


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## sse (27 Sep 2011)

hastalavista said:


> Sunny South East: From the OP's post it says its a slab over the UFH
> 
> I would imagine that the builder decided to do this before any walls as its much easier, just pour and powerfloat



No, the OP's post does not mention the word "slab", which is why I asked rather than assuming anything. At least when we were building the more usual floor construction was slab-insulation-membrane-UFH-screed, with the UFH only going in once the roof was on.

If the concrete has been poured in the open then the risks identified by the other posters are well-founded. We waited days for dry weather to pour our footings, the builder wouldn't proceed.

SSE


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## onq (27 Sep 2011)

(nods) 

SSE is correct.

The OP mentions "floors" as opposed to "slabs", and I dealt with the two most used options for self-builders - standard slab and raft.

SSE's floor construction is more usual and I'm wondering did the building someone pour a screed in the rain, which would have been disastrous.

Perhaps the OP could clarify the construction details 



ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                                as a defence or support - in and of  itself  -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                                Real Life with rights to inspect and issue         reports    on     the         matters    at      hand.


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## bullworth (27 Sep 2011)

I seem to remember that concrete is often ''cured'' by keeping it wet  for 7 days to a month so will the concrete not strengthen as it dries anyway ? Is keeping it wet for a while not advantageous to its' final strength ?


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## onq (28 Sep 2011)

Keeping it cool is the thing, which is often done by keeping it wet.

However this cannot be done when its first poured for reasons explained in the link I posted.


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                                 as a defence or support - in and of   itself  -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                                 Real Life with rights to inspect and  issue         reports    on     the         matters    at      hand.


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## BICIP (29 Sep 2011)

discuss with your engineer...excessive rain willl affect surface layer and may reduce strength although most concrete is overspecified - determine what the design mix was (from the builder) and get prof advice....miht be worth taking a core out of it and crushing it to get the actual compressive strngth of the slab to compare versus design mix...btw im talking about a slab not screed here!


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## Cyrstal (3 Oct 2011)

Thanks a million for all the replies.  We are pretty ignorant when it comes to house building so my husband is getting the engineer to check it....I am really worried to be honest, but the engineer didn't seem too concerned when we rang him,  he is checking over the coming days.

They have started the blocks of the house now as well, and it is up to window level so not sure what would happen if the poured concrete is wrong? Would they have to burst it up, would this damage the UFH....

I can't answer the questions on whether its the finished floors or not....or slab or screed!!

Can't wait for engineer to have a look at it now....

Thanks for advice, will let you know outcome.

C


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## onq (3 Oct 2011)

Depending on the severity of the damage its usually possible to scabble back any weak concrete and introduce some sort of finished wearing course and your engineer can advise you. The wild card in the mix is the UFH pipework and whether this will be damaged in the operation


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                                 as a defence or support - in and of   itself  -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                                 Real Life with rights to inspect and  issue         reports    on     the         matters    at      hand.


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## Baracuda (3 Oct 2011)

Would be very ususual to pour concrete on UFH pipes infact I have never heard of it before. Concrete is a poor conductor of heat when compared to many of the floor screeds used today

It is more than likely that they used a sand cement screed. Rain on to this finish is never a good idea as it washes the cement out of the sand and then the screed begins to ravel as a result. However a binding agent (the name escapes me) can be poured on to any area that this happens to and this will fix the problem.

We had the same problem when we built our home but all was fine when the builder poured this stuff onto the floors so its not the end of the world and only cost about €60 to put right!


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## sse (3 Oct 2011)

Baracuda said:


> Would be very ususual to pour concrete on UFH pipes infact I have never heard of it before. Concrete is a poor conductor of heat when compared to many of the floor screeds used today
> 
> It is more than likely that they used a sand cement screed. Rain on to this finish is never a good idea as it washes the cement out of the sand and then the screed begins to ravel as a result. However a binding agent (the name escapes me) can be poured on to any area that this happens to and this will fix the problem.
> 
> We had the same problem when we built our home but all was fine when the builder poured this stuff onto the floors so its not the end of the world and only cost about €60 to put right!



When we were looking at building methods (2004/2005) I seem to remember that there was a floor make-up which had the UFH under the foundation "slab", but for various reasons this wasn't recommended, the main one being that you'd be paying good money to make the worms nice and warm.

OP - I'd recommend you get your engineer to discuss this very thoroughly with the builder, to check that the correct amount of edge insulation etc. has been used. It's more usual to build blockwork on the slab and then add the UFH etc.  later when there's a roof on, every SB I know has done it this way. Was it definitely UFH and not services pipework etc.? Let us know!

SSE


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## onq (3 Oct 2011)

As long as the insulation is underneath the slab the heat will stay in the house.
Its more to do with the response time of UFH - never a rapid response option - and the use of the slab as a heat reservoir.

A lightweight 50mm screed with insulation directly beneath it has low mass and heats up far more quickly than 150mm of concrete with insulation beneath it.
UFH seems to be best used where it sets the baseline temperature with radiators used where a boost is needed, otherwise the UFH lag means a sudden hot spell can overheat the entire house.


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                                  as a defence or support - in and of    itself  -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                                  Real Life with rights to inspect and   issue         reports    on     the         matters    at      hand.


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## Baracuda (3 Oct 2011)

sse said:


> When we were looking at building methods (2004/2005) I seem to remember that there was a floor make-up which had the UFH under the foundation "slab", but for various reasons this wasn't recommended, the main one being that you'd be paying good money to make the worms nice and warm.
> 
> SSE


I think you may have picked me up wrong. Concrete subfloor poured then 50mm HD insulation on top then UFH pipes laid on insulation were and covered in a sand cement screed this was flooted off before the walls were risen so floors are perfectly level


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## Baracuda (3 Oct 2011)

onq said:


> otherwise the UFH lag means a sudden hot spell can overheat the entire house.


Don't think that is much of a problem in this country for the last couple of winters


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## sse (3 Oct 2011)

Baracuda said:


> I think you may have picked me up wrong. Concrete subfloor poured then 50mm HD insulation on top then UFH pipes laid on insulation were and covered in a sand cement screed this was flooted off before the walls were risen so floors are perfectly level



Looks like it, sorry, I assume everybody else wanted to get the shell done first  to get out of the rain!!

SSE


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## onq (3 Oct 2011)

Baracuda said:


> Don't think that is much of a problem in this country for the last couple of winters



Correct. 

Its usually on days like today - first week in Ocober and its over 20 degrees.


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## onq (3 Oct 2011)

sse said:


> Looks like it, sorry, I assume everybody else wanted to get the shell done first  to get out of the rain!!
> 
> SSE




I can understand this confusion.

I've never seen UFC placed before the house at least had a roof on and weathering fans over the opes.

Still, it goes with the detail - under screed can wait until the roof gets on,whereas if its under slab, you'd want your slab giving stability to the walls long before that.


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                                   as a defence or support - in and of     itself  -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                                   Real Life with rights to inspect and    issue         reports    on     the         matters    at      hand.


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## Cyrstal (6 Oct 2011)

Thanks for all the replies.

The engineer visited the site the other day and said that he was happy with the finish of the slab - he said it had a 'good power float finish to it '.  

So I think it's set our mind at ease a good bit!


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## onq (6 Oct 2011)

Was it power floated?

Did he test it to see how durable it was?


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                                as a defence or support - in and of  itself  -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                                Real Life with rights to inspect and issue         reports    on     the         matters    at      hand.


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