Jump to content

Pouring slab in current conditions?


RichS

Recommended Posts

Has anyone poured their Kore Passive Slab in the sort of weather we are currently having, i.e. generally falling below 0c on a night time??

 

Mine has been ready to pour for a number of weeks now but I have held off and held off because I obviously don't want it to freeze. Only problem is this is very frustrating as I feel time is slipping by when I could be getting the walls up.

 

I'd guess the fact that it is encased in EPS negates a lot of the cold weather issue but the surface could still be affected, would covering with sacking and then tarpaulin be enough to negate this risk??

Link to comment
Share on other sites

Is this going to be the finish floor. ie no screed on top. 

Tbh if it was my job and this is a finished slab I would not pour below 5 degrees and would want a good 24hour period of not below 2 degrees after the pour. 

But there must be blokes further north than me who have to deal with lower temperatures so they might disagree. 

 

Remember you only need a window of say 48 hours of 5 and above. 

Its very mild down here at the mo, have a look on the forecast. 

Link to comment
Share on other sites

Can you get hold of some straw?

 

Concrete gets warm as it cures, so if you can put some sheeting over the top, then cover it with some straw or other insulation, you should be fine.  The chances are that the slab itself will warm up enough to stay well above the local air temperature.

Link to comment
Share on other sites

Our slab was poured by MBC in slightly milder conditions than this (down to around zero on the first two or three nights after pouring) and we had terrible problems with spalling.

 

There may well have been other factors involved in our pour, but personally wouldn't risk it if you're relying on a decent surface finish.

Link to comment
Share on other sites

Thanks for all of the replies.

Unfortunately Jeremy I don't  have access to straw and the sort of problems Jack has encountered are exactly what I am trying to avoid as this will be the finished surface.

It looks like I will will just have to try and be patient and wait for milder weather to return as suggested by RG and Mr Punter >:(

Thanks again.

Link to comment
Share on other sites

Spalling is often caused by surface cooling only, and doesn't need freezing temperatures to occur.  Water has a maximum volume at around 4 deg C, so if the surface gets down to this sort of temperature after curing has started, then expansion of trapped moisture just below the surface can cause spalling. 

 

However, part of the curing process for concrete is exothermic, so the slab will heat up for the first few hours of the cure.  The secret is to stop that heat getting out in very cold weather, hence the suggestion of adding a layer of straw over the top of a sheet.  Any insulation material would do the job, as the slab will not lose heat downwards, both because the ground will be around 7 or 8 deg C under the slab and because of the insulation.  If you can find some spare sheet insulation that would work, as would erecting some form of tent over the slab and putting in some form of heating.  It doesn't take much, if you can keep the air above the slab at a temperature above about 6 or 7 deg C then it should be fine.

 

Brickies used to cover newly built walls with old sacks and a tarpaulin to keep the wall warm enough overnight in very cold weather (maybe they still do), and it's only really the first 24 hours or so you have to worry about, after that the risk of any problem occurring is much reduced.

Edited by JSHarris
Link to comment
Share on other sites

@Russell griffiths. Initially I was going to pour the slab myself. I then realised that I will need to pump some of it in due to the distance from where the wagon can get to. At this point I did a search for local pump hire companies and found a set up about 60 miles away from me who do a pump and lay service. I got a quote from them and they were just within an acceptable bracket so I think I will just pass it over to them. They use Breedonflow self compacting concrete so the levels, in theory, should be spot on.

 

I have used Kore for the insulated slab materials and have done all the preparation works myself. I hired a 3 ton mini digger to dig out and got the spoil removed by a grab lorry, lots cheaper than skip hire. I then had 10 deliveries of 20 ton loads of stone to spread and lay along with 18 tons of blinding before laying Kore's system.

Link to comment
Share on other sites

16 minutes ago, RichS said:

@Russell griffiths. Initially I was going to pour the slab myself. I then realised that I will need to pump some of it in due to the distance from where the wagon can get to. At this point I did a search for local pump hire companies and found a set up about 60 miles away from me who do a pump and lay service. I got a quote from them and they were just within an acceptable bracket so I think I will just pass it over to them. They use Breedonflow self compacting concrete so the levels, in theory, should be spot on.

 

I have used Kore for the insulated slab materials and have done all the preparation works myself. I hired a 3 ton mini digger to dig out and got the spoil removed by a grab lorry, lots cheaper than skip hire. I then had 10 deliveries of 20 ton loads of stone to spread and lay along with 18 tons of blinding before laying Kore's system.

Interesting. We used a mix by Breedon that was self compacting last month, we laid it during Storm Caroline (300mm slab on sheet metal decking). Weather forecast changed 2 days before pour and it froze the night after the pour. There is a thin layer of water on most of it just now but I'll check and see how the surface looks. So far it looks fine but I've not been near it for ages! 

Link to comment
Share on other sites

The key with any of the self compacting concrete mixes is not to over work them - they will level to an extent but still need a bull float or similar over them to finish the job. The downside is that they seem to be made of smaller aggregate and more sand so the more you work them to get them flat, the more liquid and cement you pull to the surface. 

 

If you’re using it as final floor (polished..??) then take the advice of the polishing and finishing company as to what they want as otherwise it could be costly. 

Link to comment
Share on other sites

1 hour ago, RichS said:

@Russell griffiths. Initially I was going to pour the slab myself. I then realised that I will need to pump some of it in due to the distance from where the wagon can get to. At this point I did a search for local pump hire companies and found a set up about 60 miles away from me who do a pump and lay service. I got a quote from them and they were just within an acceptable bracket so I think I will just pass it over to them. They use Breedonflow self compacting concrete so the levels, in theory, should be spot on.

 

I have used Kore for the insulated slab materials and have done all the preparation works myself. I hired a 3 ton mini digger to dig out and got the spoil removed by a grab lorry, lots cheaper than skip hire. I then had 10 deliveries of 20 ton loads of stone to spread and lay along with 18 tons of blinding before laying Kore's system.

Photos be nice!

Link to comment
Share on other sites

  • 3 years later...

I am resurrecting this old thread as I am watching the cold weather now for my concrete pour for my insulated raft foundation. Anyone else doing the same?

 

At the time of writing (February 2021) it looks like overnight temperatures will not consistently rise above 4ºC for another month (!?!) in Cambridge if long term weather forecasts are any guide.

 

And then my concrete team will probably have a backlog of pours to do.

 

Patience is a virtue – I need to be more virtuous!

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...