Hi,

I am redoing my shower. The plumber has fitted a new shower tray & I am
looking to retile the area so the plumber can fit the shower cabinet &
shower.
The existing tiles were fixed to 10 mm plasterboard. The plasterboard
was in turn attached to the (solid brick) walls by blobs of cement
which means that there is actually an 11 mm gap between the walls & the
back of the plasterboard (21 mm from the wall to the front of the
plasterboard).

Removing the tiles revealed that the existing plasterboard in the
bottom half of the shower area was very wet & needs replacing. I have
cut away a large area of the wet plasterboard & removed the cement
attaching it to the wall.

I plan to replace the plasterboard I removed with multiboard. However,
I am not sure how to attach it.
I need to re-create the 11 mm gap between the wall & the the new
multiboard so that it is flush with the plasterboard that doesn't need
replacing.

Presumably I need to use the same method as was used before - ie cement
the multiboard to the wall? If so, what sort of cement should I use? Do
I just put lots of blobs of cement to a depth of say 15 mm & push the
board into the cement until I get the multiboard flush with the
existing plasterboard? Do I put the cement on the multiboard or the
wall?

Any help much appreciated. I have never worked with cement before.

Thanks,

Johnny