My concrete supplier automatically adds a 'heat' additive to the mix during the winter.  I will be pouring a 56in garage foundation with 6in blocks in -3c (26.6f) weather. A few questions: Do you guys still insulate the top of the pour when cold weather addtives are used? Should I expect winter-concrete used in ICF to harden significantly faster and warn my guys on the vibrator to be on their toes? ICF is not too common where I live, are there any questions regarding additives I should quiz my supplier on?   Any other tips or insight on this subject greatly appreciated.

As you likely know concrete creates heat as it cures. I have read a study that for flat work (driveways and shuch) 28 degree F is the optimal temp. It make the concrete cure slow and hard. But colder then that it freezes and breaks apart. So you make the choice of how close to 28 degrees you want to get.

The ICF will insulate and keep the concrete warm, but what about for the next week after?

I you can stay near the job site you could use a thermal temp gun to measure and keep an eye on it. I think you will be fine.

I poured mine in this temp and was fine. But you could add a role of insulation on top, or something similar, as needed.

I'm not sure what a heat additive is. Where I am in upstate NY the suppliers use hot water to make the mix. This alone accelerates the reaction. What we do is order a stiff slump, usually a 2. At the job site we add a mid-range water reducer which will raise the slump to a 7 or 8. This reaction last about 45 minutes before it goes back to a2. A 2 is a really dry mix so freezing shouldn't be a problem unless the temp really falls. In really cold weather we have used unfaced fiberglass on top. This will wick the moisture out the top. You should not use plastic sheeting on top. There are two ways that the wall dries. The top and the footing. If you cover the top it will slow the drying. Hope this helps.

Cover any exposed concrete with insulated tarps, batts, rigid insulation, etc. At that temp (barely below freezing) you could probably just cover the top with some lumber. The heat generated by the concrete curing process will do the rest!

No need to heat/horde with ICF typically as the forms trap the heat from concrete (unless engineer on site deems heating necessary - then bow to their ultimate superiority )

We are in warmer southern Oregon. Our suppliers just use hot water during the colder weather. We tend to be conservative and we don't pour concrete if the 10 day forecast has freezing temps. I am sure the folks up north would be the best source of info on how best to successfully pour concrete below freezing temps when pressed to do so. For us, good schedule planning goes a long way to avoiding these sort of pressing issues.

Hey everyone. The days after the pour were extreme cold. I ended up using about 4-5in of straw on the top of the wall. My father had the idea of using our walkway planks to weigh the straw down and keep it from getting blown away. The wood also doubled as insulation.

The bottom of the wall had at least 10in-16in of straw over the footings.


I would go out periodically and put my bare skin hand between the straw and concrete - it was very obvious that the straw was working and that the concrete was not going to freeze - to the point that i didnt even bother to grab anything to check the temp.

We backfilled on day 6.

Since you covered the top you are fine, winter builds absolutely suck horribly, but can't predict what/when people are ready to build. Keep the straw on as long as possible, the cure is very slow in ICF adding cold temps makes it even slower

Coldest I poured was -23c, biggest problem that day was the pump operator was pissed, I had to take liability for any damage to his pump - fortunately none

I probably would have waited a few more days on the backfill and had the floor system installed prior to putting the dirt back in

Heh. If I'd poured on Saturday, the last week or so has been 40+ degrees the entire time! AND THIS IS CHICAGO!

THIS is why when someone screams about "Global Warming", Chicagoans turn around and go "We'll take TWO!"

It's actually like early spring this week! I can get things cleaned up a bit. Im sure the Cold + Chicago wind separates the men from the boys!

Chris, i really struggled with the early backfilling. It was more to do with when my brother-in-law was available... And wanting to get everything under frost depth ASAP. He dug down to dry unfrozen fill to help with settlement and i guess that reduces pressure. I also felt comfortable with it only being a 4ft high stem wall. I eyeballed the longest wall a few times expecting the worst but the wall never moved.

Posted By 2p2 on 27 Dec 2019 08:16 PM
It's actually like early spring this week! I can get things cleaned up a bit. Im sure the Cold + Chicago wind separates the men from the boys!

Have a couple clients just off Lake Shore Drive by Grant Park.

At certain times of year, trying to just walk around up there feels like the "super breath" fight scene from Superman II.

Talk to the ready mix supplier and agree on a temperature of the concrete. Send it back if it is any colder than that.