Laying Marble on Concrete Screed

[clipboard2008]

Hi

I have a customer that wants me to tile their hallway and also a changing room for their swimming pool

The hallway (30m2) is currently laid with parquet flooring which was stuck down with a bitumen product. The bitumen has bled through and stained the grout lines in their dining room (this was done by the previous tiler)
Obviously the customer doesn't want this to happen agin so I'm thinking I've got 2 options:
a) Seal the floor with Ardex P51 to stop the possibility of bitumen bleeding
b) Ditra the floor which would definitely stop the bitumen bleeding but also add to the cost
What are you're thoughts?

With regard to the changing room (22m2) on a concrete screed. The customer is most probably going to go with a porcelain product on the floor. Again would I be best using Ditra due to the water that is likely to be sat in the changing room?

Thanks

[garythetiler]

The bitumen will need to be removed as much as possible before you install anything over it, the ditra will work well in this circumstance but i would still try and remove the black jack before laying it ,try to ensure at least an r10-r11 slip resistant tile in the changing area