I am looking to lower part of a kitchen ceiling. In this 'part' corner there are two RSJ steel beams which form two out of four sides. Both the beams are covered with pink fireproof plasterboard. Pic: https://e1.pcloud.link/publink/show?code=XZMzoRZGYcSmzueUEjjuW4tyKcSAzQIHIhX Existing pic of ceiling: I want to use up spare insulation by 1) putting a wooden frame (blue sticks) for plasterboard to screw upward into (see pic: https://e1.pcloud.link/publink/show?code=XZCzoRZyTIl4yyhiLHv8Vq1quo8PV992P1k) and 2) screw plasterboard (large blue square) upward through the wooden frame (pic: https://e1.pcloud.link/publink/show?code=XZOzoRZVk4x8GanVKpM4B1gaTR2Oj8wfLWV ) I have been told that the pink fireproof fireboard (plaster) needs to be skimmed. Do I need to skim the plasterboard before I put this false ceiling up? Or do I not need to skim the fireboard and put the false ceiling up straightaway?