I have a bathroom wall that I'm wanting to re-grout. I've removed the old grout, and have found there's a space between the back of the tiles and the wall. The tiles seem pretty solid though (after pushing on them, they don't seem to be going anywhere).
The problem is when grouting the vertical gaps in the tiles, the grout just falls through and into the space between the tile and walls. I'm not sure how the original tiler/builder managed to grout this.
I was thinking of packing the gaps with material (foam I guess?) so the grout has something to sit on. Does that seem right? Or are there an other ideas out there?