Is it safe to pour concrete and use mortar in freezing weather?

Question

I have a 1947 cape (Cape Cod style home) in New England. The basement egress walls which are made of unfilled cinder blocks and run parallel to the house under the porch are caving in. I thus have to have them broken up and have new walls built--of cinder blocks, rebar, and filled with concrete, layer by layer.

Because of the freezing weather, I had thought that I should wait until spring or summer to have this done. However, one person I have spoken to has told me that there is no need to wait for the spring thaw. Because of the headache of the current egress collapsing, I am very wary of anything that could weaken the new walls, and so am uncomfortable with the idea of pouring the concrete for the egress walls in the winter. I have read that it is possible to pour in freezing weather, but the process seems rather elaborate and uncertain.

So, my question: Is it generally a bad idea to pour concrete in freezing weather? Should a rebuild such as this be done after the threat of a freeze? As to freezing weather, it's difficult to predict how cold it may get, as it's been a warm winter. It will get as low as 16 degrees F this week during the late night and early morning hours, but in past years has gotten much colder than that, and may this year.

Answer 1

Yes, you can pour concrete in freezing weather, but it’s complicated.

First of all, you’re talking about “grouting” cinder blocks, not pouring concrete.

There are many sites you can Google for “cold weather concreting”. I’d stay with a site that refers to ACI standards. Here’s one:

https://www.concrete.org/Portals/0/Files/PDF/University/306R-16_excerpt.pdf

Many of the procedures for cold weather concreting is the same as for mortar and grouting AND may require a “tent” over the work area so you can heat the work space.

I would only attempt this with an experienced cold weather concrete contractor. I’d also review procedures with him so you both have a clear understanding of what is expected by the contractor if: 1) the weather turns colder than normal, 2) time delay maintenance of construction site waiting for weather to change, 3) costs for extreme cold weather delay, etc.

I’d also define the lowest temperature the contractor can work in and who will monitor the site to verify compliance with: A) thawing of ground (if you’re pouring on ground), B) maintaining air temperature around work site during work and curing period, C) maintaining drum temperature, etc.

As you can see, it is possible to work in cold weather, but it’s expensive AND risky. The contractor knows he’ll be working slower and doing less than working in warmer temperatures...so he’ll increase his cost to account for the risks. You may want to wait for better weather.