Scraping mortar

We found that a hammer and wood chisel worked well for removing the mortar (although it probably wasn't very good for the chisel.

 

Also, remember the blue waterproofing membrane? It turns out that the mortar sticks to the blue stuff better than the blue stuff sticks to the backerboard. I guess this makes sense because the blue stuff is supposed to isolate the tiles from the backerboard.

Done