Laying yorkstone flags in kitchen - advice please

[redkite]

I live in an 1880s house and am just about to rip the kitchen out and start again. On lifting up a small piece of floor to see what was lurking beneath, I came to some very nice fine-grained local (West Yorkshire) flagstones, with low iron content, sitting on an earthen base (clay). On top of that a thinnish layer of mortar had been laid and board on top of that (and linoleum on that). No dpc is present and damp penetration has caused the board to break down. Not bad damp at all though - rest of the house has earth floors, with air gap, below joists and nice and dry..
What I want to do is lift the flags, clean them, re-lay them and seal them. The level will have to be raised since there is a small extension with solid concrete floor and I'm not digging that up. So I'll have to raise level of the original kitchen by about 60-75mm
I know there are bits and pieces of advice around this great site (wish I had discovered it before I remodeled the garden) about flags but I can't find all the answers. What I need to know is:
1. Best advice on what to lay over the earth floor to bed the flags on - presumably I need to put in a dpc over the earth floor also
2. best way to clean the flags - prefer not using harsh chemical cleaners (can they be sanded? Are abrasive sheets available?). If harsh chemicals unavoidable - what to use?
3. Best pointing to use bearing in mind this is a kitchen floor and will be regularly mopped and I don't want food debris lodging in the pointing (and the dog brings in piles of mud)
4. Best sealant to use
I could just tile the whole thing but I'd love to reinstate the flag floor in this Victorian House and I've got some in the garden I could raid to floor the extension part.
Many thanks for any advice any of you flooring experts can give.

[matt h]

Lay dpc then subbase, then concrete screed. you could then lay flags in the concrete before it sets, or you could use floor levelling compound with added sand to bulk it out then use floor levelling compound neat to bed the flags, and finish off with flexible flooring grout between the flags. The main site gives other methods of laying flags, and should be consulted before you decide which way to go. Rand A is the cleaning expert , there are so many different cleaners about, but i have found geocel do a patio cleaner which has done the business for me in the past which is bio degradeable.

[lutonlagerlout]

i would do100 mm subbase first ,then 25 mm softsand,then DPM then 100mm concrete ,then flags into the concrete or bedded on top with mortar
pointed with sand cement mortar and sealed with lithofin mn stainstop
IMHO

LLL

[RAPressureWashing]

Redkite,
On the cleaning side, other then the mortar, what else is there? is it just general dirt, carbon deposits etc. Any chance you could post a photo of the stones say the worst one?