Cold Weather Concrete Tips
Tips on Pouring Concrete in Cold Weather
I have poured many a concrete slab in cold weather. It is always a challenge. The cold temperatures make working that much more miserable. If you get wet, you really become miserable. No doubt this type of activity is not for the faint hearted! What's worse, once the pour begins, there is no turning back. That concrete coming down the chute is like liquid gold! A mistake or goof can cost thousands of dollars.
Frozen Ground or Snow
Don't pour concrete on frozen ground. Not only can the ground freeze the concrete from the bottom up, you can have catastrophic cracking when the ground thaws. There will no doubt be hollow spots beneath the concrete. Driving over the hollow spots will create tension, which in turn creates cracks.
Pouring concrete over snow simply adds unnecessary water to the concrete. We have already discussed why this is not a good idea.
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Foundation Walls and Cold Weather
Is your house going to be built in cold weather? Watch out for pouring foundations in cold weather! Remember a foundation wall is simply a vertical slab. However, they have a disadvantage. They are exposed on three sides once the forms are pulled! Foundation forms should be well insulated and left on for three to five days if at all possible.
If your foundation contractor removes the forms too quickly, the concrete will have absolutely no protection! If they must remove the forms, absolutely install the insulation blankets immediately. If you have extended cold weather don't allow the foundation to be backfilled. Temperatures below 14 degrees F completely stop the hydration (crystal growing) process. Once temperatures rise above that, the chemical reaction resumes, but very slowly. It could take a long time for your foundation walls to gain enough strength to resist the pressure of backfill dirt.
Low Slump + Lots of Help = Success
Low slump concrete is hard to work with. It's backbreaking work. But in cold weather is can mean the difference between success and failure. Think of it, why not hire (or have your contractor hire) two to three additional people for the one to two hours it will take to place the stiff concrete. Once in place, screeded and bull floated, those guys can take off. What did it cost? $100 - 150? Is that worth it to insure that you will not have bleed water problems? Low slump concrete will allow you to finish the slab quicker. That will allow you to get blankets on the slab quicker. It's a good idea!