Encasing Deck Framing - NOT GOOD PRACTICE
There appears to be a growing trend, probably for aesthetic reasons, to encase timber deck bearers and posts and other structural members in either masonry veneers or rendered 'blue board' type external surfaces. As can be seen in the photograph below, this trend is resulting in premature decay failure of the timber members as water will enter and be trapped by the encasing.
Even if the timber is of the required natural durability of Class 1 above ground or H3 treated pine, the decay hazard created by encasing is equivalent to an in-ground one as there is no ventilation or ability to be free draining and to dry out.
A more appropriate practice would be to stand the desired external finish surface off (19 mm-ish) and sark the member(s) so the structural timber is allowed to free drain and leaving an air gap to enable some chance of air circulation and drying. Moisture should not be allowed to be trapped by full encasement.
Source: Timber Queensland Technical Update 27 Oct 2016