Foundation pour end of December in Zone 6?
Due to timelines, our foundation will not be poured until mid-end December (Central WI, zone 6). The 5’ stem walls will have exterior insulation but no insulation is planned to extending on the ground away from the footings. They plan to use an additive that would allow the concrete to be poured in freezing temps. Because our area can be a wet area in the spring, they are building up which means that until the forms are pulled away, the walls insulated, and the ground backfilled around the walls, the full walls and footings would be exposed to freezing temps for a period of time. Is this an issue for heaving and stability of the foundation? Any other issues we should be considering?
The walls are prebuilt off-site and this as well as the roof would be placed and installed in February. The other things I wonder about is freezing or even negative temps and it’s effects on adhesives, tapes, caulking, ect.
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Down to a little below freezing, you can "tent" (lay poly over everything) the concrete and the natural heat from the ground plus the heat from the curing concrete will be enough to keep things safe. The accelerant they are using to do the pour in lower temperatures will usually come with the tradeoff of weaker concrete and more difficult working conditions. I try to avoid the need to use accelerants if at all possible. I'd watch the weather and see if maybe you can use regular concrete mix and tent things. In my area (CZ5), that usually works into December as long as it's not unusually cold.
Once the concrete has cured you shouldn't have to worry about freezing anymore. It's just during curing where freezing is a concern.
Bill
How long is the curing time usually before you don’t have to worry about it? Also, the temps in our area during December is an average of 27 as a high, so I’m guessing that means tarping to gain heat from the ground won’t work?
I allow for a week for the concrete to cure, but it's technically not "fully" cured for a month. After a week though you're pretty much past the danger zone.
The average temperature and tenting plus the heat from the concrete (concrete gives off heat as it cures) has to keep the concrete above freezing. Weather conditions play a big part in this. If 27 is your daily high, it's probably safe to assume the daily low is a fair bit below that, so you're probably in the "too cold" territory unless you add a heater ($$). In my area, we tent when it will get down to freezing or a "little" below, maybe down to 25*F or so as the daily low, if that. It's similar to the difference between a frost, where tenting your garden can save the plants, and a hard freeze, where the plants are going to die regardless of what you do unless you run a heater.
Bill
can be with an indirect construction heater and poly. we call them trunk heaters for the long trunk tubes you can put together to pipe heat where you want it. added benefit is the fan in the heater pushing the air keeps the poly 'ballooned' up.
I am working on a civil project right now in Alaska where we are using one to keep our bedding material from freezing overnight. also using concrete blankets laid out on the ground to keep it from freezing.
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Emil,
There are two separate issues. The possibility of frost heave, and those associated with curing concrete in cold temperatures. I have worked on multi-family projects where both occurred after winter foundation pours. I'm not sure anyone can give you assurances they definitely won't be a problem.
Is there a temperature you see that is usually safe if we have a warm week? I’m wondering if we could watch for a warm week and try to time it.
Emil,
As I understand it the problems occur if it gets colder than 40F. I've seen it poured in temperatures a lot colder than that, but I've also had jobs where they had to demolish walls that didn't cure properly.
A fully exposed, free-standing wall, is something of a worst case for freezing while curing. A slab, especially if slightly below grade, is probably a best case scenario. The slab basically has it's entire underside surface area on ground, which is a bit warmer than the cold air. A wall has the majority of it's surface area exposed to cold air. My work usually just involves slabs (slabs to set equipment on primarily), and tenting usually works well for that. For a wall, unless it was in a narrow trench below grade, I'd be reluctant to rely on just tenting if expect lows are going to get down near freezing and stay there for very long (i.e. several hours to overnight).
I like to use my earlier analogy: if it's going to be cold enough long enough to kill unprotected garden plants, then you need to be concerned with your pour.
Bill