am fitting a kitchen next week where every square inch of wall is tiled. decided rather than removing the tiles and potentially re-plastering the whole room to overboard the tiles with battens and tapered edge plasterboard then tape and joint the whole room. some sections (bulkheads / window reveals etc..) are tight and if i were to batten and board the finished surface would be above the window frames. is it feasable to dot and dab straight onto tiled surfaces? if so do i need to do anything to the tiles beforehand such as uni-bonding etc...? also, is tapered edge plasterboard (one taped and jointed) ready for decoration (wallpapering / painting) or do i need to give it a coat of emulsion or some sort of primer?