Relaying old flags indoors

[Patsy1]

Hi,
I have uncovered a flagstone floor in my kitchen, from under various layers of concrete. I need to re-lay about 1/3 of the flags as they dip quite badly.
It looks like soil and lime underneath, pretty damp too.
Should I re-lay them on sand or should I be using a membrane. My concern is the floor 'breathing'. I did the same in the adjoining room last year (no flags lifted, just layers of concrete removed and top layer ground off) and it's still not dried out fully.
Pic. of the horror attached

 

[bobasd]

you asked questions about flag floors in March this year - then disappeared from your own thread?

gently tap the skim of sand and cement and it will break away.
carefully lift the flags with two people slowly prising them up.
take the flags outside and clean them off.

you need a sectional view from soil to FFL of what i propose below - you need it as a guide to working accurately.
dig out the soil, sand & lime to the required depth - then tamp the soil surface down.
lay a membrane DPM that will flop up the walls for 150mm or so above the FFL.
next lay insulation with edge insulation as well.
then pour concrete 100mm or so.
then bed the flags on top of the concrete.

thats the professional method of doing it, and there should then be no damp penetrating through the flooring.

fwiw: i can see what looks like blue membrane on the right side of the pic?
with the existing floor you could be liable to rising damp in the walls?
that pipework looks pretty iffy?

 

[Patsy1]

Thanks bobasd.
I've read that using a membrane could send the damp up into the walls, which as you rightly pointed out do have a very poorly fitted membrane. Is that something to consider?
I can't take the flags outside as doing this on my own, but cleaning won't be necessary as when re-layed I'll be grinding the surface off with an angle grinder with grit flap disc as they are very pitted and flakey, this worked well last time.
Yes, pipework iffy. I removed the fitted kitchen yesterday and found them like that.

 

[bobasd]

are you saying the blue membrane is acting as a DPC in the walls - that would be very odd?
do you understand the difference between a DPC and a DPM?
if you have a sound, properly located DPC in the walls then any rising damp will be stopped at the DPC line.

have the walls been Dot & Dabbed or had any kind of tanking treatment - better, showing more, photos would help?

unless you can clear all items off the floor and out of the room you wont be able to do what i suggest above.

 

[Patsy1]

No, not saying blue membrane is acting as a DPC
Yes, I understand the difference between DPC & DPM
There is no DPC
Yes, walls dot & dabbed, no tanking treatment, previous owner installed an electro osmosis DPC which has since rotted away

Thank you for taking the time to reply bobasd

 

[FX]

Hi Patsy,

Are your external walls pointed with lime mortar and what about the internal walls - lime plaster or lime mortar behind the dot & dab?
There is a risk of damp from under the floor being 'pushed' outwards and into the walls if you lay a DPM but if the walls are lime mortar/plaster any damp will still be able to escape. Therefore it may well be okay to lay a DPM.

Have a look at limecrete and foam glass on the MikeWye website - I'm not affiliated to it or him but it provides some useful information.

 

[Patsy1]

Thank you FX, I will take a look at that website.
Yes, external walls are pointed with lime mortar, not sure about the internal walls yet.

 

[bobasd]

you dont seem certain why the blue membrane is there? what function does it have? i suspect that its been used behind the D&D linings as a tanking membrane or vapour barrier?

somehow or other get a look behind the D&D lining and then post pics - there could be mould and damp at work.
are any of the walls in that room outside walls?
whats happening on the other side of any or all the walls?
is there a chimney breast in the room?

what state is the external render in?

DPM's can sometimes drive below floor moisture to become rising damp in the surrounding walls - but for the time being your best concentrating on the above.