Pouring Foundations in Winter
Pouring Concrete Foundations in Winter is
Tricky Business but is Doable if the Right Precautions are Taken
By: Mark J. Donovan
For one reason or another a builder
or homeowner may find him or herself pouring a foundation in winter. Pouring
concrete foundations in winter can be a risky venture. If not done without
taking the necessary precautions, or if the temperature is just simply too cold,
there is a risk that the concrete may freeze prior to it curing. If this happens
the foundation walls could be severely and permanently compromised in strength.
In addition, the concrete may experience cracking or spalling, where the
concrete literally splits, flakes or show signs of pitting.
So why does the concrete run the risk of experiencing these types of problems
when pouring foundations in winter?
The answer to this question is in
the curing process itself of concrete. Concrete both needs and produces heat
to properly cure. If the ambient air temperature is so cold that it too
rapidly draws the heat out of the concrete while it is curing, the concrete
may not set up properly and the water in the concrete could actually freeze.
As a result, the foundation walls could be dramatically weakened and
possibly exhibit cracks and spalling.
For maximum strength and reduced risk of cracks and spalling, foundation
contractors prefer to pour concrete when the temperature is expected to be
above 40 degrees Fahrenheit for 3 consecutive days.
usually pay very close attention to the weather forecasts during the winter
months. In extreme northern climates they may even shut down operations during
the dead of winter.
In situations where pouring the foundation walls in temperatures below 40
degrees Fahrenheit is a necessity, foundation contractors will include an
anti-freeze admixture in the concrete to help prevent the water from freezing
and thus enable the concrete to cure properly.
Years ago when I built my vacation
home in central New Hampshire we were forced into pouring foundation walls in
winter. It was January and the temperatures fluctuated between 20 and 40 degrees
Fahrenheit for days. Finally we had a window of warmer weather, the January thaw
if you will, and poured the foundation walls. In addition to waiting for mildly
warmer weather, our foundation contractor also took additional precautions
including mixing in some calcium chloride into the concrete, and insulating the
walls with hay after pouring the concrete to help keep the heat in, slow the
curing process and prevent freezing.
He also asked the concrete plant to heat the concrete prior to delivering it
to our site. Fortunately our foundation is still crack free, but suffice it
to say, it was a nervous phase during the construction of our home.
In regards to the use of calcium chloride in concrete, our foundation
contractor used about a 2:100 ratio of calcium chloride to concrete. The
calcium chloride lowers the freezing temperature of water and thus helps to
prevent the water in the concrete from freezing, which enables the concrete
to have sufficient time to cure properly.
Photo By Mark Donovan
In addition to the precautions
already mentioned when pouring foundations in winter, foundation contractors can
also ask the concrete plant to include air-entraining admixtures in the concrete
mixture. Air-entraining admixtures help by trapping tiny air bubbles into the
concrete mix so that any freezing water in the concrete has a place to go
without damaging the foundation walls. The foundation contractor can also ask
the concrete plant to include more cement in the concrete mixture to help the
mix more quickly gain strength to handle the freezing temperatures. Adding more
cement to the mixture, however ads more cost to the cement.
To conclude, pouring foundations in winter is possible as long as the right
precautions are taken and the temperatures are not so extremely cold that the
admixtures simply canít do their job. Make sure when interviewing foundation
contractors you ask them the techniques they normally employ when pouring
foundations in winter and see if they match any of the above recommendations.
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