I believe it's like 54 degrees, hopefully someone else can jump in if I'm wrong this. We use warm water if the dry ingredents are cold. Wendy

This might help.
from http://www.calciumchloride.com/concrete.shtml

Why Calcium Chloride in Concrete?
Investigations have shown that a two per cent addition of calcium chloride has equal cure strength at 50F as plain concrete has at 70F. Regardless of the temperature or cement type, concrete mixes containing calcium chloride will always have a faster cure rate than plain concrete. The beneficial effects of calcium chloride will be even more pronounced at lower temperatures. The accelerated cure rate measured as final concrete set time can be reduced by two-thirds when two per cent calcium chloride is added - two hours compared to six hours for plain concrete.*

I don't know what OR if they added anything, but a basement was poured last week down the road, at 36 degrees.
I'm in Central Wisconsin, and frost at night yet. Frost line is still rather deep. They plowed the snow, dug the hole set up forms and poured.
Doubt this helps.....just my 2 cents worth.
Marcia

Temperatures for casting leaves would be different then pouring basements as the added ingredients we don't need for that fast of curing-maybe some do for some reason, but in my humble opinion less chemicals the better. Wendy

My driveway and patio were poured in late December without incident and was "walk on" firm in two days. The tin layer of ice and snow that formed on the "blankets" that first evening did not affect the pour. Although many cement contractors are reluctant to assist DIYer, many of their laborers are not. I gained a lot of information from a worker with 10 years experience in concrete work. The adding of calcium chloride is a boon to concrete work and has been successfully used for years.

I am not a chemist: I am a creative artist. As artist we strive to create better and varied art pieces. We experiment with both new and old ideas (some work some don't) or like many other "schools" we stagnate, people lose interest, and the art form dies. I think I will try some calcium chloride in a batch of peat moss tufa just to see the effect. The heat generated by the calcium chloride might reduce the curing time that is such an impairment to many successful tufa projects. There is also the possibility that the inclusion of calcium chloride would be an aid when making thin set garden spheres.

As far as, "less chemicals the better" I am lost. We humans are nothing more than a living, breathing chemical factory.
However, here are some of the uses for calcium chloride (CaCl2) that you might find interesting.
As an ingredient, it is listed as a permitted food additive in the European Union for use as a sequestrant and firming agent with the E number E509. The anhydrous form has been approved by the FDA as a packaging aid to ensure dryness (CPG 7117.02).
Calcium chloride is commonly used as an Electrolyte and has an extremely salty taste, as found in sports drinks and other beverages such as Smartwater and Nestle bottled water. It can also be used as a preservative to maintain firmness in canned vegetables or in higher concentrations in pickles to give a salty taste while not increasing the food's sodium content. It is even found in snack foods, including Cadbury Caramilk chocolate bars (purpose unknown).
It can be used to make a caviar substitute from vegetable or fruit juices or added to processed milk to restore the natural balance between calcium and protein for the purposes of making cheese such as brie and stilton. Calcium chloride's exothermic properties are exploited in many 'self heating' food products where it is activated (mixed) with water to start the heating process, providing a non-explosive, dry fuel that is easily activated.
In brewing beers (esp. ales and bitters), calcium chloride is sometimes used to correct mineral deficiencies in the brewing water (calcium is important for enzyme function during the mash, for kettle protein coagulation (the "hot break") and yeast metabolism) and adds permanent hardness to the water. The chloride ions enhance flavor and give a perception of sweetness and fuller flavour, whereas the sulfate ions in Gypsum, which is also used to add calcium ions to brewing water, tend to impart a drier, crisper flavor with more bitterness.
Aided by the intense heat evolved during its dissolution, calcium chloride is also used as an ice-melting compound. Unlike the more-common sodium chloride (rock salt or halite), it is relatively harmless to plants and soil

I'll be using quikwall and won't be adding anything but liquid to it. I'm using it to make fake rocks not pour a foundation. I don't want to lose any strength integrity by mixing the liquid into it when it's too cold and using a cold mix. We just had 8 inches of snow overnight with more in the forecast. I think I'll try to change the workshop to later in the month when the temps should be warmer....SHOULD be warmer. No point in working with crete when everyone's miserable. I hate this global warming.

fleur, I know what you are talking about, this cold weather is getting the better of a lot of us. Yesterday we worked in the yard, today we are huddle inside looking out at the sleet. Was anxious to get the lawn etc cleaned up before the real warm weather and the actual 'casting time' begins - but seems like this spring it's one nice day a week is all we are allowed. This morning I checked my 'to be painted' stock and found a medium size cast leaf to paint-kept me from looking out of the window and grumbling, lol
Good luck with your rocks, I know you do great looking work, I like to 'surf and lurk' during the cold weather (smile) Wendy