I'm a bit confussed, but can't you just pack the 20mm with broken slate
tiles? I raise part of our floor that way. Jack up the joist with a car
jack, put in the slate shimm and relax the jack.

Scott


Sure I could, but the point is that the wall around the fireplace area
hasn't just settled downwards a bit, it has developed a noticeable lean out
of vertical. If I just pack onto the top of it, I'm worried that it will
collapse (at some future point when the floor is well and truly covered with
expensive tiles...).