Casting in Cold Weather (Another Thread)

[nybyggarn3]

Hello,
I can't find any answers that match my conditions, so I'm starting another thread on the subject.

I am going to cast a slab for my future outdoor kitchen, 4.2 x 6.5 meters. The slab will be cast now in late autumn in Västerbotten. I'm planning to build the mold with 195x45 studs and insulate with 100 mm cellular plastic.

The forecasts ahead are about 5 degrees Celsius during the day and down towards zero at night. You probably have to allow for the temperature to creep down to a few degrees below zero, but not worse than that. Thankfully, the weather looks to stabilize, so I am hopeful that we will hit a day when it doesn't rain.

My question is what are the appropriate measures against cold in this specific scenario?

 

[prototypen]

The concrete station can deliver warm concrete and then you cover with double layers of lightweight tarpaulin.
The concrete stations can do this.

Protte

 

[Workingclasshero]

https://www.byggahus.se/forum/threads/gjuta-fast-kantsten-hur-stor-aer-frysrisken-nu.327730/
Maybe you'll find something here.

/W

 

[nybyggarn3]

The concrete station can deliver warm concrete and then you cover with double layers of lightweight tarps.
The concrete stations know this.

Protte

Thanks for the reply. It sounds rational. How low in temperature would you say that method is sufficient?

Do I just lay the tarps directly on the wet concrete? Isn't there a risk of disturbing the surface then?

 

[prototypen]

You can cover once the concrete has been laid and then demolish and grind, and then you can walk on the concrete and there will be no marks if you carefully pull the tarp on again.

seems like you have poor knowledge of concrete, hope you have someone knowledgeable when to demolish and grind.

Protte

 

[nybyggarn3]

You can cover the concrete once it's laid and then remove and sand it, at which point you can walk on the concrete and there will be no marks if you carefully pull the tarp back on.

seems like you have little knowledge of concrete, hope you have someone with expertise for when to remove and sand.

Protte

It's true that I'm not an expert on concrete. When I built the house, I did all the groundwork myself but brought in a guy to help me with the actual casting. The plan is the same setup this time.

The concrete guy's comment when I talked to him was that it's not worth waiting until the slab can be walked on. His suggestion is that we lay out the concrete and finish the surface as well as possible while the concrete is wet. He mentioned some kind of steel with a handle. I guess it’s combined with a screed. If we're not satisfied with the surface, we'll sand it later.

Maybe it's a crazy plan; what do I know. The fact is that the outdoor kitchen will adjoin a sandy beach, and I envision that the fairly rough surface could work.

 

[nybyggarn3]

I followed the advice (or hint) and called the concrete station. They confirmed the advice to cover immediately with a thin tarp and that it should be sufficient, i.e. no insulation or heat is needed in such mild cold.

Furthermore, the guy claimed that it should take a few hours for the concrete to set so that it can be smooth troweled or scraped. Then the question arises, how should we handle the slab that we are going to use as the floor in the outdoor kitchen? Scrape, hand trowel, or even use a helicopter trowel?

I understand that it is a matter of taste, but perhaps someone has an opinion? I have full confidence in the concrete guy (retired concrete worker) but communication is not his strong suit. It's easiest to offer a ready-made preference.

 

[nybyggarn3]

Then the slab was poured. The concrete was 20 degrees when it was laid out. Covered with insulation immediately after pouring, hand-troweled in the afternoon, and then covered again, now with double tarps.

The tarp is not touching the concrete but is about 20 cm above it on boards that hold it up. This is because the surface was a bit soft even after troweling. I've thrown a lot of stones around it so it won't draught underneath.
The forecasts for the coming days are a few plus during the day and around freezing at night.

I'm wondering if my measures against the cold are sufficient? Or should I use a fan under the tarp? The guy at the concrete station didn't like fans.

Also, I'm wondering how long it takes before critical strength to withstand freezing is achieved? I plan to uncover and remove the formwork on Saturday (after 4 days) if it has been long enough.

I would be very grateful if someone knowledgeable could take the time to answer.

 

[nybyggarn3]

I can add that I have a thermometer that measures the temperature in the middle of the mold. Unfortunately, not in the concrete but in the air under the tarp. Now 10 hours after pouring, it shows 9 degrees (it's 2 degrees outside). A reasonable assumption should be that it is slightly warmer in the concrete.

 

[Snickarkirre]

If the thermometer shows 9 degrees under the tarp and it's two outside, then the slab should be curing. If you stick your hand under the tarp and feel on/just above the concrete, do you feel any heat? If the concrete has just started curing, it generates heat by itself. You should be able to remove the formwork on Saturday. You don't have to remove it with a sledgehammer, though...

 

[nybyggarn3]

If the thermometer shows 9 degrees under the tarp and it's two outside, the slab should be curing if you stick your hand under the tarp and feel just above the concrete, do you feel any warmth? If the concrete has only just started to cure, it generates heat by itself. You should be able to remove the mold on Saturday. You don't have to remove it with a sledgehammer though...

Thanks for the response. I found a diagram online showing how long it takes for concrete to reach the critical limit of 5mpa. If I interpret it correctly, it takes about 2 days if the concrete holds 5 degrees, and the concrete doesn't seem to drop in temperature under the tarp. So on Saturday, both the tarp and mold will come off. The sledgehammer can stay in the shed...

 

[Snickarkirre]

Oh perfect, then it's all calm! Haha that sounds good