fire-protective covering

HB50

means:

(a) 13 mm fire-protective grade plasterboard; or
(b) 12 mm cellulose cement flat sheeting complying with AS/NZS 2908.2; or ISO 8336; or
(c) 12 mm fibrous plaster reinforced with 13 mm x 13 mm x 0.7 mm galvanised steel wire mesh located not more than 6 mm from the exposed face; or
(d) other material not less fire-protective than 13 mm fire-protective grade plasterboard, fixed in accordance with the normal trade practice for a fire-protective covering

Source - BCA Vol 1 terminology