We are experiencing unprecedented cold weather in the Carolinas, and it seems like I am getting into conversations with clients and collegues almost daily about some of the specifics of cold weather concrete operations.  I thought I would address a couple of the questions that I am frequently asked.

Q: What is the minimum temperature to pour?
A: There really isn’t one.  There are places where they do year round pouring in the snow.  However; contractors in these areas are obviously better prepared for working in the cold.  They have equipment such as heated/insulated blankets that help keep work area above freezing, and they follow a completely different process than we do.  Cold weather pours require deep footings, extensive sub-bases, and even a heavy dose of calcium in the concrete to help it cure faster.  Obviously, this also affects the pricing.  I have done some online research where it is not uncommon for contractors to charge over $10 per square foot!   This is almost 4 times my minimum, and over 3 times what I have ever charged on a job over 1,000 square feet.
Q: Can Baja Concrete work in cold ops?
A: Of course!  Typically in NC the best thing to do is wait out a cold spell, but if it is necessary we can work in the cold.  Concrete keeps itself warm during the curing process, and it usually isn’t affected until temperatures drop below 22 degrees.  I try not to pour on consecutive days of below 25 weather unless the client pays extra for insulation.  I have had contractors insist that the concrete will be fine in cold weather ops uncovered, but I am a strong believer in “better safe than sorry”.  If concrete is not covered correctly, the water from the concrete during the curing process can raise to the surface of the concrete and freeze on top forming a small sheet of ice.  Without the water in the mix, the concrete is weakened.  You may have seen flaky concrete before on the top layer of a driveway or walkway that chips off like paint when you drag your feet on it.  This is usually the result of a lack of water in the mix.  Also, when concrete loses its intended mixture ratio during the curing process, it loses its PSI strength and can crack much easier.
So in cold weather we can use calcium in the mix, we can cover it with plastic and hay, or we can just wait out the cold spell.  I am open to what the client feels most comfortable with.  The one thing I won’t do is risk it.  I would rather not do a job, than to do it incorrectly regardless of what the client (contractor, home owner, or business owner) might say.