Currently my house is specified using dot and dab to attach insulated plasterboard to the inside of the Porotherm inner leaf. The inner leaf will be plastered first with a parge coat so air behind the plasterboard shouldn't be much of an issue.   I would prefer mechanical attachment with the plasterboard hard against the blocks, but the contractor reckons Porotherm is too awkward for the number of fixings required. You cannot use standard fixings as the blocks are hollow.   Y