which has a decorated outer surface 14 the adjacent edges of adjacent panels are separated by a substantial space 22 in fig2 and 3 it can be seen that each panel 13 is provided with a rear surface 15 which faces toward extends parallel to and is substantially spaced from the surface 12 of the structure an elongated primary support element 16 extends from the center of the rear surface of each panel 13 an elongated secondary support element 17 is fixed to the surface 12 of the structure and extends at a right angle thereto the primary and secondary support elements 16 and 17 are provided with conjugate surfaces 18 and 19 respectively to lock them rigidly together the fastener 21 extends through the support elements 16 and 17 to prevent unintended separation the space 22 between the adjacent edges of adjacent panels 13 is sufficient to permit human access particularly to allow the arm of a mechanic to reach to the rear of each panel and to the fastener 21 the secondary support 17 is provided with a base 23 which is welded to the vertical surface 12 of the structure 11 conjugate surfaces 18 and 19 consist of an external cylindrical surface 19 on the support element 17 and an internal cylindrical surface 18 on the support element 16 fig4 shows particularly well the manner in which the pin 21 extends through an aperture 24 on the support element 16 and an aperture 25 on the support element 17 a stop 32 is provided along the shank of the pin 21 and a grasping ring 33 is provided at its upper end referring again to fig2 it can be seen that the rear surface 15 of the panel 13 is provided with an.