An apparatus and method for molding a substantially hollow building panel of the kind having spaced opposed outer panel walls interconnected by a plurality of spaced formations such that adjacent formations each define a void therebetween. The apparatus includes a mold having means to define an outer surface of at least one of the outer panel walls and a plurality of spaced apart inflatable void forming plug members connectable with an inflation means, disposed within the mold. The apparatus further includes a means to introduce a settable wet mix into the mold.