Floor screed - Replacing floortiles

[grumpygramps-2007]

I live in a 2hundred year old stone cottage so lots of things to do.any way the back room floor has tiles similar to marley tiles but a lot thicker. as some are loose I had the bright idea to lift one to find there bedded on soil. would It be alright to put a dpm down & screeding the floor about 2inches thick or is it concrete then a screed. cheers gramps.