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#32
Thanks for the good idea.You mentioned in your opening post that the cut to the underside of the window would be 30mm, there looks to be plenty of room to pick the sill up with a couple of pieces of plasterboard, that could make your cut closer to 55/60mm. I quite often alter the reveals to suit set out, if of course it's possible.
Just measured it and could go all way up another 35mm which would actually bring it to match the top section of the window frame. Just mechanical fixings screw the layers of plasterboard together & into the window revel or tile adhesive between each layer as well / instead of? would be a few layers?