How much wall re-prep before tiling?

AlwaysSomething

I have agreed with my tiler that I will knock off the old tiles before he comes to fit new tiles. Here is the result: There is a lot of old adhesive left on the wall in places. In some places, the skim coat has come away, along with the top layer of the plasterboard, leaving a dark paper texture. What do I need to fix before tiling, and what can I leave as it is. Thanks

Cornucopia

I wouldn't get too worried about what you've already got there. Unless there are big bumps (more than a few mm) or similar holes, then the new tile & grout will cover over most problems. Take off anything loose, though.

If you are looking to try to remove the old grout, I've found the easiest way is to use a filling knife (the broad bladed type) flat against the wall, with the blade on the edge of the old grout. Tap it gently with a mallet and the old grout should chip off in reasonably large pieces.

Depending on the situation, it's also feasible to tile over existing tiles.