To provide a slate reinforcing method for carrying out treatment for restraining dust scattering or the like in attachment removal work from a slate surface and forming a reinforcing member and a paint film layer with weather resisting and heat insulating effects after the treatment to improve durability or the like, and further forming a layer for covering an attachment and all to restrain dust scattering or the like, and to provide a reinforced slate.

The reinforced slate 1 is constituted to superpose a reinforcing layer 3, the reinforcing member 6, a backing layer 4 and a surface layer 5 in this order from the one closer to a slate base material 2. The reinforcing layer 3 forms an asbestos powder scatter restraining layer by applying 1/3 of the applied amount of an infiltration primer to the surface of a base material and hardening it or the like, and the layer is hardened only on the surface without infiltrating into the base material. Attachment removal or the like on the surface of the base material is then performed. When the remaining 2/3 of the infiltration primer is applied to the surface of the slate base material 2, it infiltrates from the porous base material surface, reaches a degraded part 21 and a sound part 22 and becomes hard to form the reinforcing layer 3.