What does the drying method for cold wall refractories prohibit?

The drying method for cold wall refractories prohibits excessive exposure to moisture because moisture can significantly compromise the performance and integrity of the refractory lining. When moisture is present in a cold wall refractory, it can lead to issues such as hydrolysis, delayed setting, or even thermal shock during initial heating phases. This is particularly critical because cold wall refractories are typically designed to operate under less than optimal conditions and require careful management of their drying process to achieve the desired physical properties. By avoiding excessive moisture, the refractories can develop the necessary strength and thermal stability required for efficient operation.

In contrast, other options do not align with the primary focus on moisture management. For instance, while heating from the hot face might not always be recommended for cold wall refractories, this approach is sometimes used strategically in refractory applications. Direct sunlight isn't a major concern for the integrity of refractories during drying, although environmental conditions should be monitored. Layered heating can be beneficial in certain contexts as it allows for more controlled temperature increases, which can be advantageous in specific applications.