An acoustical panel for forming a monolithic ceiling or wall, the panel extending across a rectangular area, and having a core made primarily of gypsum, the core being essentially coextensive with the panel area such that it has two opposed sides, each of an area substantially equal to the area of the panel, the core having a multitude of perforations extending generally between its sides, the perforations being distributed substantially uniformly across the full area of the core and being open at both sides of the core, the face side of the core being covered by a porous layer, the perforations being optionally restricted at a rear side of the core, the porous layer at the face side of the core being suitable for adherence of drywall joint compound and a water-based non-blocking paint.