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Discussion Starter · #1 ·
Hi. This is my first post here. I'm a 2nd year carpentry apprentice Located in Montreal. I'm currently in the process of building our family cottage and I joined this community for construction advice.

I'm almost done with building the forms, and next I'll be laying 4 inches of rigid insulation over the crushed stone, a vapor barrier, then rebar @12" oc. By the time I finish the plumbing and the formwork (and depending on the weather) it would be cold to cure the slab for the first 48 hours. (ask me for more details if you need)

My question is, will the rigid insulation underneath help with the curing, as well as some blowed heating over the slab? I was advised not to use accelerators in the concrete mix to avoid rusting of rebar. Any other options out there? I will have a team of concrete finishers do all the concrete work, but I'm thinking I might have to deal with the curing process.

Thanks for your help.

George
 

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Who advised you about accelerators? Call your redi-mix company. They should have a non corrosive accelerator--that's what we use in the winter in Minnesota.

Regarding foam, yes I think it will help the pour quite a bit, as the heat from the concrete curing will not be absorbed by the ground. If you can get it it poured and hard enough to trowel and walk on, you just pull insulated tarps over it and you're good. If you don't have access to tarps I suppose you could use a layer of poly and then straw. It will be toasty warm under the insulation, no matter what the temp is outside.
 

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Discussion Starter · #6 ·
Who advised you about accelerators? Call your redi-mix company. They should have a non corrosive accelerator--that's what we use in the winter in Minnesota.

Regarding foam, yes I think it will help the pour quite a bit, as the heat from the concrete curing will not be absorbed by the ground. If you can get it it poured and hard enough to trowel and walk on, you just pull insulated tarps over it and you're good. If you don't have access to tarps I suppose you could use a layer of poly and then straw. It will be toasty warm under the insulation, no matter what the temp is outside.
If I can't get access to insulated tarps or straw, I guess I can use poly and more rigid foam on top? Would I have to mist the slab with water occasionally or is there no need for that when it's cold?
 

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No need to mist it. The surface will stay damp under the covers. You don't need to do anything but cover it with insulation of some kind. Again, the hard part in the winter is getting it set up enough to trowel and then cover. Foam would work, though it is expensive and it would have to be weighted down so it won't blow away. Maybe you can use it elsewhere in your build.
 

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Discussion Starter · #8 ·
No need to mist it. The surface will stay damp under the covers. You don't need to do anything but cover it with insulation of some kind. Again, the hard part in the winter is getting it set up enough to trowel and then cover. Foam would work, though it is expensive and it would have to be weighted down so it won't blow away. Maybe you can use it elsewhere in your build.
I checked the price of straw, and it's actually pricey. I might use the rigid boards since i will reuse them on the walls later, and will weigh them down. Hopefully using the right accelerator, having a good team of finishers, and getting nice weather will make things easier. Thanks for the help Marson.
 

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Use 2% accelerator. It will speed up the hydration process creating faster heat. And you will not have to wait forever to get on it to finish it.
 
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ACI allows 2.0% calcium chloride for plain concrete that is dry and free from moisture when in service. It lowers to 0.3% for reinforced concrete.
Rebar @ 12"o.c. is a bit steep for a general cottage slab, good for a bunker though. Minimum strength is 2500psi for interior slabs, but garage slabs are 4500psi and use of/tracking in de-icers will definitely change the exposure of chlorides present.

There are non-chloride accelerators too. Just rely on the mix plant, they will follow ACI-318 to a 'T' (I assume even in Canada?).

Edit: just noting for others reading the 2500/4500psi is for severe weather conditions like in Montreal, not Florida.
 

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ACI allows 2.0% calcium chloride for plain concrete that is dry and free from moisture when in service. It lowers to 0.3% for reinforced concrete.
Rebar @ 12"o.c. is a bit steep for a general cottage slab, good for a bunker though. Minimum strength is 2500psi for interior slabs, but garage slabs are 4500psi and use of/tracking in de-icers will definitely change the exposure of chlorides present.

There are non-chloride accelerators too. Just rely on the mix plant, they will follow ACI-318 to a 'T' (I assume even in Canada?).
When they do that type of slab here they go nuts with the rebar too
 

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Discussion Starter · #13 ·
ACI allows 2.0% calcium chloride for plain concrete that is dry and free from moisture when in service. It lowers to 0.3% for reinforced concrete.
Rebar @ 12"o.c. is a bit steep for a general cottage slab, good for a bunker though. Minimum strength is 2500psi for interior slabs, but garage slabs are 4500psi and use of/tracking in de-icers will definitely change the exposure of chlorides present.

There are non-chloride accelerators too. Just rely on the mix plant, they will follow ACI-318 to a 'T' (I assume even in Canada?).
yeah 12" o.c. because we're getting prepared for when the mole army attacks the surface people :p
I will rely on the mix plant to provide a good ratio, like the 0.3% you suggested.
 

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Discussion Starter · #16 ·
That 2nd floor structure would bear on the exterior walls, and if any bearing down on a wall on the interior of the slab, should have a thickened slab for that. Columns would need a larger footing.
There's a total of 6 columns, holding up a built ridge beam, and each column has a footing of 24"x24"x12". Here's a section of the slab.


629806
 

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A real Frost Protected Shallow Foundation in the flesh! Don't forget the wall anchor bolts.
Just a side note, Zorplax: A frost protected foundation only works if you heat the cottage all winter long.
If you winterize the plumbing and let the cottage go cold, all the insulation in the world won't prevent frost from heaving that slab foundation.
If the cottage is seasonal, you might consider a full depth frost footing instead.
 

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Discussion Starter · #19 ·
Just a side note, Zorplax: A frost protected foundation only works if you heat the cottage all winter long.
If you winterize the plumbing and let the cottage go cold, all the insulation in the world won't prevent frost from heaving that slab foundation.
If the cottage is seasonal, you might consider a full depth frost footing instead.
It will be an all-season cottage and it will be heated throughout winter. The walls will be R-27 and the ceiling R-31.
 

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Nice. That doesn't sound like much ceiling insulation for Canada. Here in Cleveland we do R-49. You lose more heat through the ceilings than through the walls. And of course the biggest loss is through the windows.
 
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