Just undertaken my first tiling DIY project, to fully tile kitchen & bathroom, Kitchen walls turned out super but the kitchen floor tiles have lifted. I was told by a friend I should have gave the old tiles a coat of PVA before tiling and then the tiles would have stuck down and not came loose - is this correct. Also could it be possible I did not put on enough pressure to the tiles when putting them down, I lightly tapped them with a rubber hammer and piece of wood. Any advice appreciated before I start the bathroom floor.