50 degrees Fahrenheit

I was afraid of that. The days are ok, but the nights are too cold. I was really hoping I didn't have to wait until Spring.

Thanks for the reply!

I can not speak to the technical reason - but know from past failed attempts that cold weather and concrete do not mix well. Some of my early attempts at making Christmas presents resulted in craked pots. Maybe you can bring the tufa inside in the basement or warmer garage for the few weeks that it will take to cure. Keep it moist as long as possible.
Mike

If you have a section of your basement you could use you can still make 'mud stuff' throughout the cold winter months. My DH and I made several 'crete' Asian style lanterns this past winter. Just proceed as you would outside, misting for 7 days etc. The first one we made in the fall, left it in the basement until cured. After a few weeks I placed it on the deck during a warmer rainy spell, then left it outside for the rest of the winter placed on a rock above the koi pond. The lantern is still standing and in great shape. Wendy

I have found that because of the amount of dust from the three ingredients that it is safer to work outside or some place that has a big open door. I have done a few projects inside and even with a mask end up sucking up lots of dust.
Portland dust in your lungs is not good. your choice. ML

Mike, you are absolulutly correct to give this warning out to syllabus. We also used masks however we only mixed small amount at any one time in buckets and once wet there was no dust. Also smoothed out any rough edges while green
(the very next day), and swept up all drops of bits and pieces of crete while still damp. Our biggest mess was dropped sand on the floor. Thanks Mike for giving syllabus the health warning, something I should have done in my 1st. post. Wendy

Thanks for all the comments, guys. I'm sure there are others out there that this info has helped. I'm going to have to wait until Spring to work on anything as we do not have a basement or a garage. And even if we did have a basement... from my experience of working w/ these materials outside (always w/ a mask), I wouldn't want to be doing any of it in an enclosed space. Besides the dust it all creates... I am waaaaaay too messy! LOL!