Back-blocking is a reinforcing system designed to minimise deformation and cracking/peaking of joints that can occur under a combination of adverse job and weather conditions or building movement, especially in large ceiling areas.
This reinforcing consists of laminating cut-to-size strips of plasterboard to the back surfaces of sheets directly behind joints using plasterboard cornice adhesive. Back-blocking forms part of the plasterboard lining standard AS/NZS 2589:2007
Back-blocking is strongly recommended as an added precaution for longitudinal recessed edge plasterboard joints in ceilings and for butt or end joint walls and ceilings. Where mid-span butt or end-joints are not required, but are used to minimise plasterboard wastage, these joints must also be back-blocked.