An adequate amount of entrained air is essential for durable exterior concrete in cold climates, but too much air can reduce strength without improving durability. Tight tolerances for air content cause technical difficulties for producers. Factors such as the dosage of air-entraining admixture, the size of sand used in the concrete, batching methods, mixing technique, and concrete temperature all affect the entrained-air content in concrete. Erratic air contents can be controlled, first by ensuring that content measurements are made correctly, then pinpointing the cause of the swings in air content. Changes in sources of cement, fly ash, admixtures, and aggregates can all cause erratic air content. Batching equipment that is dirty or worn is also a source of problems.