Where we are tiling floors we have put down 18mm thick ply sheeting across the joists and then we put down Schuluter Ditra matting. We used Balls F44 glue with their P131 primer for porous surfaces such as wood. You also need to use a special trowel with serated edges to spread the glue.
This needs a day to go off and we are ready for tiling. More to come soon!
