pouring cement in winter

jmc · Dec 5, 2003

Its time for putting in a cement floor in the new pole barn. Next week the temperatures should range from the mid 40's to the mid 20's at night. Is this too cold for good concrete without some kind of additives? Do the additives weaken the cement significantly? Yes, I should ask the contractor but he wants to keep busy and also, probably does not have a 20 yr perspective. It could wait until spring since its got a compacted gravel base but it would be nice to have it done.

Thanks.

John

kn6md · Dec 5, 2003

I believe some accelerators attack steel, but your contractor would know about that. I had a garage slab poured in early November of last year (Carson City area of Nevada) and the contractor ordered hot water in the mix to get things going. I let it cure for a month before I drove on it. My guess is that if your contractor came highly recommended, you and your slab will be just fine.

Regards,

Bill Vorhies

JASTN70D · Dec 5, 2003

The good side is that the slower it cures the stronger it is. the bad side is that if it freezes before most of the water is out it could present a problem. I have seen where it is covered with straw at night if they don't use an accelerator of some type. It seems everyone does it different. And time to finish is the driving force about how it gets done. If your just getting a bull float/brush finish I would not use an accelerator

Junkman · Dec 6, 2003

I have been told that they put calcium chloride into the cement to keep it from freezing. I don't advise pouring a floor in freezing temperatures and would avoid it at all cost. One of the problems is that the floor always leaches out the salts and this is corrosive to anything that it comes into contact with, such as steel. If you can have it poured without the calcium, and cover it with plastic and hay, it will not freeze unless the temperatures drop drastically. When I worked on a home construction site one year in college, the contractor would never pour in the winter and they always got all the foundations in during the fall. Many times, the foundations would just sit until the framing crew got to them.. The contractor isn't going to live there, so they don't have the same concerns as you would as the homeowner...

DUMBDOG · Dec 6, 2003

They poured the cement in my pole barn in November, sealed up all of the vents and used heaters for a few days to let it cure properly. After three years the only cracks that I have are at the end of the expansion cuts.

Wildman1 · Dec 6, 2003

I had the option of pouring in November in Alaska on a new addition. After checking this out 2 problems were found: chances of a substandard floor and significantly higher costs due to additives and heat. So....I waited until spring.

rtimgray · Dec 6, 2003

This is going to seem really picky, but the terms "cement" and "concrete" are not interchangeable. Cement is a component of concrete, not the final mixture. If you actually poured cement, you would have a big, cracky mess.

Sorry jmc, it's not just you that does that - tons of folks do and I know what they mean but it bothers me. My boss at work once told me "you know, we should pour a cement curb around that mixer to keep the water from spilling" and I said "you mean concrete, right" and he said "ah...same difference". So I really wanted to pour a cement curb...but then I decided I wanted to keep my job.

If your low temperature for 4 or 5 days is going to be 20 degrees, and you really want the floor poured, I'd say just add hot water and cover it when you're done (concrete generates heat as it cures). If you can stand to wait until spring, then go ahead and wait and you know you can't go wrong.

Again, sorry about the cement:concrete thing; just struck a nerve.

have_blue · Dec 6, 2003

You will need about 4 days with temps no lower than mid 20's. Concrete generates its own heat while curing, that's why it takes colder temps to freeze it. Plastic film would be good insurance if temps threaten to go into the mid 20's before the 4 day period is up. Slow curing in cold weather make it stronger than normal.

TimSullivan · Dec 7, 2003

Thanks for the post. We are trying to decide whether to start a home in New York State. The weather here can vary in the winter and we were hoping for some warmer temperatures. The nights have been in the teens or low twenties and I just don't want to pour in that range.

Looks like we will be waiting until spring which was the original plan anyway.

5030 · Dec 7, 2003

I'd wait until late spring, when the temperature is stabilized.

You can use calcium chloride as an accelerator but anything that's in contact with the floor when you begin to use it that is of a ferrous nature will corrode due to the leaching effect of the calcium chloride.

As you already have your gravel base, just put some more skirt boards on the uprights to keep the snow out and pour in the spring.

It would be much easier on you and the floor will probably last longer.

PineRidge · Dec 7, 2003

4 years ago in Jan. the builder mixed calcium chloride in the concrete for the basement and garage floors when building our home. A year later they spiderweb cracked. Not real bad, but I would wait if I had it to do all over again.

Junkman · Dec 7, 2003

I would also suggest that you wait till around June when the ground has sufficiently warmed and the moisture is mostly out of it.... this is the best time to pour concrete. Make your appointment with the contractor now for then. Most of them schedule work long in advance.

bebster · Dec 8, 2003

To quote from an article on this subject: "Calcium chloride is not an antifreeze agent. When used in allowable amounts, it will not reduce the freezing point of concrete by more than a few degrees. Attempts to protect concrete from freezing by this method are foolhardy." Article on Calcium Chloride

"Calcium chloride should not be used where reinforcing steel is present. "
Another Article

I'm inclined to agree with most of the posts here that it is better to wait until the chance of freezing is minimized, assuming your schedule permits. The risks and costs of trying to pour and cure concrete during the freezing winter months might not be worth it.

gordon · Dec 8, 2003

Ask if high early is avaliable in your area. It's concrete with a #5 portland instead of #1 portland. It's ground finer for more moisture contact and hardens much quicker.

Sill needs to be covered with blankets in real cold temps.

Good luck
Gordon

jmc · Dec 8, 2003

Thanks all, for the good information. Its a tough call but my impatience won. We pour tomorrow. The contractor says if we cover it with straw/visqueen (sp?), and since its inside a shell, we'll be ok without additives. Got a salamander heater lined up as a backup plan.

Junkman · Dec 8, 2003

consider putting 6 mil plastic under the floor to keep the dampness down in the summer months..... if the contractor says that will keep it from drying fast enough, you can put some slits into the plastic to allow the water to drain through and it will not hurt the plastic barrier from doing its job later on. This is how one of my cellar floors was done and it works great....

em14 · Dec 8, 2003

I would not slit the moisture barrier instead try to maintain it's integrity. Moisture will find that slit and you may have a moisiture problem in the future. The concrete should be placed with as stiff a mixture as you need to maintain the proper "slump". It will dry all in good time and your contractor knows that. Don't rush it and spoil it ... The contractor will be long gone and your money spend when the concrete fails. I also would not pour concrete in freezing weather unless I could heat it. Just for what it's worth ...
Leo

RonL · Dec 8, 2003

Junkman

Concrete sets by chemical reaction, not by drying. If concrete dries out before it has properly set it will result in a weaker concrete. Plastic moisture barrier on grade keeps moisture from intruding after the building is finished, but it also keeps moisture from leaching out before the concrete has set properly. It also serves as a radion barrier when it is properly installed.

RonL

Junkman · Dec 8, 2003

Leo:
Just for what it's worth....... I couldn't disagree more! I have a few slits in the plastic in my garage floor and there is no perceivable moisture coming up from the floor. I was not recommending that it be sliced and diced, but rather one or two for every 100 square feet. I will agree with you not to pour concrete in freezing weather and I have already said so.
RonL:
I know that concrete sets by chemical action, but the liquid, more commonly known as water has to evaporate also. The small amount of water that pools at the bottom of the pour would normally be absorbed by the dry ground that the slab was poured on if no plastic were used no matter what time of the year it is poured. As for this causing a problem, I sincerely doubt that is the case, because bigger projects than this one are routinely poured without the benefit of plastic barrier, such as footing for foundations, bridge abutments, etc.

Disclaimer: This is not a flame or a battle ground, but just a different opinion between 3 people with a divergence of opinion on the subject matter.... /forums/images/graemlins/smirk.gif I respectfully submit that we can agree to disagree and that the opinion of one might not necessarily be the correct one..... /forums/images/graemlins/grin.gif

em14 · Dec 8, 2003

Beleive me I'm glad that your basement has no moisture problem. However, I would not wait for the moisture in concrete to exit such a small slit as you suggest cut. I would think that the majority of the water in your basement concrete left the concrete via evaturation as in the normal curing process or you had a very dry base and a number of slits and I hope that you never had a mositure problem to begin with. Anyway I stand by my previous and we can just disagree! I would suggest that anyone pouring concrete research the local concrete plants and local inspectors before undertaking a large pour.
Leo