To prevent the sticking of cuttings from occurring without adversely affecting a paper-machine system and not to the detriment of the recycling properties of resin by spraying an antistatic agent over the wet mat of a rock wool board formed by a paper-making process and impregnating the wet mat with the agent and further, impregnating the wet mat with a water-soluble thermosetting resin.

The wet mat of a rock wool board formed by a paper-making process is impregnated with an antistatic agent by spraying the agent over the wet mat. Next, the wet mat is impregnated with a water-soluble thermosetting resin by applying the resin to the wet mat with a flow coater. After that, the wet mat is set by drying in the same steps as for the manufacturing of an ordinary rock wool board. Consequently, cuttings generated when the rock wool board is cut in a manufacturing or an installation step do not stick to a finished product or a machine. Therefore, the appearance of the finished product is not marred, and a step such as for cleaning the machine is dispensed with to contribute to the improvement of workability. In addition, the recycling properties of the resin are not adversely affected as the antistatic agent and the thermosetting resin can be added through their mutually independent systems.