Never pour concrete on hard, frozen ground. Frozen ground will lower the temperature of concrete, causing it to set more slowly, and may even result in cracking of the concrete. First, you should remove all ice, snow, and standing water from the surface. Once the surface is clean, you should thaw it using heat pipes and blankets, or electric blankets. Warm up anything that will come in contact with the concrete to at least 0 °C. Do not use unvented heaters as carbon dioxide from the heaters may cause soft, dusting floors. Make sure that the heaters are attended at all times as they pose a fire hazard.