How to Pour Concrete in Sub-Freezing Temperatures

Excavate the area where the concrete will be located with a shovel or backhoe, and remove the excess soil from the immediate vicinity.

Place 2-by-6 form boards around the perimeter of the excavated area. Secure the ends of the form boards together with double-headed nails. Place wooden stakes at 3-foot intervals along the outside of the form boards, securing them to the form boards with double-headed nails.

Build a scaffolding system around the entire excavated area, leaving space for the concrete truck to maneuver into the area. Leave room for your concrete tools and space heaters as well, keeping in mind that the heaters must be 3 feet away from any flammable materials.

Cover the entire scaffolding with clear heavy duty polyethylene plastic, sealing the gaps with foil tape. The goal is to make the structure as air tight as possible to prevent sudden bursts of wind or cold. Cut a series of 3-inch to 4-inch slits near the top of the enclosure to allow for air ventilation. This is crucial to prevent carbon monoxide poisoning.

Set up propane space heaters inside the enclosure to bring the temperature up to at least 50 degrees. Heaters must be placed at least 3 feet away from any flammable objects. Leave the propane heaters running at the correct temperature for three days before pouring the concrete. This is to ensure that the ground temperature is at least 40 to 50 degrees and will not adversely affect the concrete when it is poured. Check the heaters occasionally to make sure they do not overheat.

Pour the concrete once the temperature in the enclosure has been 40 to 50 degrees for three days. Fill the form boards and screed the surface of the concrete with a 2-by-6 piece of lumber. Finish the concrete by smoothing it with a steel trowel, working in an arc motion. Allow the concrete to set for two to three hours.

Place sheets of clear polyethylene plastic over the concrete surface to help it retain moisture. Leave the propane heaters on while the concrete cures for three to seven days to reach its maximum strength.

Remove the plastic sheeting from the concrete slab and dismantle the scaffolding structure when the curing process is completed. At this point, it is safe to build or allow traffic on the concrete slab.