We don't have detailed knowledge of Cutek Extreme CD50, but from Cutek's Safety Data Sheet it appears to be an oil and wax blend (paraffinic distillate), with copper 8 quinolinol as an anti-mould additive. This would seem to be a satisfactory finish for outdoor timber, and should live up to most of the claims made on the Cutek website. We agree with the general statement that CUTEK® Extreme CD50 "will not flake or peel and maintenance is fast and simple – no need to sand or strip".

In Fig. 5.38 of TDG 37C timber members are protected by fire-resistant plasterboard. The glulam could be designed to AS 1720 Part 4, Fire resistance for structural adequacy of timber members, where members are oversized to provide sacrificial material that allows them to retain structural adequacy during a fire event. However, this would result in a large beam to cope with a 90/90/90 FRL. In your attached detail the glulam appears to be protected by plasterboard encasement.