A prefabricated sacrificial galvanic anode panel includes a rigid or semi-rigid backing board or similar support surface over which a thin layer of cement, mortar or adhesive is applied for holding a compliant layer of material in place on the support surface. The layer of wet adhesive, cement or mortar is sufficiently thin so that upon drying it does not cause warping of the support surface. The compliant or spongy layer is laminated or sandwiched between a thicker layer of ionically conductive galvanic mortar and the substrate support surface. The compliant or spongy layer prevents the thicker layer of galvanic mortar from wetting the backing board or substrate support surface so as to prevent warpage upon drying of the thicker layer of galvanic mortar and also accommodates the expansion of corrosion products from the galvanic anode material.