In principle, it is neither professional nor advisable to lay calcium silicate boards under or over plasterboard or plasterboard. The reason for this lies in the nature of the plasterboard or drywall: The cardboard that encases the plasterboard can be damaged by moisture. It tends to rot or promote mold growth.
Calcium silicate boards have the special property of absorbing moisture from the room air and releasing it again in a suitable room climate. However, this function is impaired by the cardboard coating of the plasterboard, which means that the benefits of the calcium silicate boards cannot be fully exploited and damage to the material can occur.
