Abstract: A prefabricated composite panel of the type comprising a supporting plywood board, a foamed sheet of polyurethane and a covering layer on the front face of the polyurethane comprising a plurality of brick slices with an aggregate in the spaces between the brick slices which is bonded into the front face of the foam is improved in its fire retardancy by providing a plurality of vertical support metal strips on the inside face of the brick slices at spaced positions across the width of the panel. Each metal strip includes a hanger element at the top which engages over a portion of the foam and a plurality of punched tabs each of which engages under a respective one of the brick slices. The support strips prevent sagging of the brick slices when heat is applied to the front face of the panel since that sagging can allow the heat to penetrate cracks in the covering aggregate.