Many people say that you shouldn't do 'tufa or concrete below 50F.

I've done it successfully if the temperature is dead-certain-sure to remain above freezing.

Curing cement creates its own heat to a certain extent, but it does cool down; how long depends upon the thickness of the project. A slab 1/2" thick will cool more quickly than a 1 ft thick slab. And when it cools down, it is still relatively fragile (esp for the kind of things we do -- much less so for freeway overpass construction).

I know that 'professional' concrete companies will pour when temps are below freezing, or going to be, but since the average American business doesn't give a rat's patootie about their work, *I* certainly wouldn't do it, nor would I ALLOW a company to pour MY concrete on days like that, no matter how much they tried to reassure me.

In my personal opinion, 'professional' concrete guys mostly don't know beans about concrete. I've heard them spout BS about it that would drop a steer. These guys are apparently trained by bozos who haven't a clue, and they keep passing on the same erroneous information.

Sue

From experience I can tell you that if you pour below 50 degrees, all bets are off about how long it will take before it is safe to de mold your project. I live in hot, humid Alabama, and most projects I do during the summer are easily ready to demold in 12 hours. The year I got a bonanza of leaves just before frost and did the next "warm" day when temps at night dropped to just below 50 took almost 3 days to be ready to demold. It seems to me that they are as strong as the others, but keep in mind that they will be fragile and easily broken for longer than if it were warmer.

Many people say that you shouldn't do 'tufa or concrete below 50F

From the Portland Cement Assoc Web site
Can it be too hot or too cold to place new concrete?

Temperature extremes make it difficult to properly cure concrete. On hot days, too much water is lost by evaporation from newly placed concrete. If the temperature drops too close to freezing, hydration slows to nearly a standstill. Under these conditions, concrete ceases to gain strength and other desirable properties. In general, the temperature of new concrete should not be allowed to fall below 50 Fahrenheit (10 Celsius) during the curing period.

I assume these people should know!

Personally I have tried to do in my garage when it was below 50 and it cracked after a few months.