Thanks for any info.
The old tiles are on solid so would be a pain to remove and re-plaster
I will be cleaning down with sugar soap first would this be enough.
How useful is brushing a diluted PVA with some sand (soft) mixed in to provide a key when dried?, does this surface play up with notched trowel? did read somewhere about PVA reacting with adhesives? really looking for proven testimonials.
Thanks for all replies Tez