preparing a concrete floor

[luke-warmwater]

I want to prepare my damp and uneven concrete kitchen floor ready for tiling (I think this used to be the scullery). It used to have laminate flooring which I've pulled up leaving a thick plastic damp-proof membrane sheet. Obviously I need to get this floor level but I also want it to be damproof. Can I use self levelling compound OVER the plastic sheeting or is that stupid? Is it best to lift and discard the the plastic sheeting and if so how can I use self leveller on this damp surface?
Any advice gratefully received.
Luke

 

[gcol]

Bin the plastic sheet and have a read of these stickies by mattysupra.
//www.diynot.com/forums/viewtopic.php?t=80131
//www.diynot.com/forums/viewtopic.php?t=80333

EDIT: Ah I see you've already asked the same question in the flooring section and been given the same advice.