I have to hang a corner wall unit, one face will go onto an exterior block wall, the other face will go onto a plasterboard "eggbox' wall, two layers of plasterboard with cardboard inside, the studs are miles apart so I cannot screw into them. Would umbrella anchors do the job (if I use several), or would I be better off fitting battens behind the unit, both top and bottom using the umbrella fasteners and then screwing into them thru the unit? I would reinforce the battens with glue between them and the wall
Sounds fine. One side screwed into wall. One using umbrella fastenings. If the unit does not have a fixing in the middle fix a bracket below into either the solid wall or stud.
Are there any other wall units to be hung extending the run on the wall where it's eggbox construction? If so, you might benefit from a hanging rail to hand the corner unit and subsequent units off (at least you can use more hollow wall fixings to fix the rail up. ).
The total on the plasterboard wall is 1 meter, the 600 cm corner unit and then a single unit of 400 cm, so I reckon all should be ok....