I've had to remove the plaster walls along the exterior walls of my 150-year-old stone house to install insulation. (I know how strongly some of you feel about removing plaster. Just believe me; it was necessary.)
In quite a few places, the old floor does not meet the inner surface of the stone wall, leaving too much of a gap to install the sill plates for the new stud walls snug against the exterior wall. In some places, we can move the sill plate onto the floor, but this will increase the cost of spray insulation since the quantity of insulation needed will increase. In other places, interior doors are too close to the wall to be able to do this without blocking the door (unless we use 2X2 studs).
Is there a way to fill and level the gaps (some kind of mortar?) in order to install the sill plates right along the wall, where I'd prefer to put them? (There will still be gaps between the new studs and the exterior wall, since the walls are anything but straight. This is an advantage, actually, for spray insulating.)