Insulate concrete floor under tiles - limited space!!

[kristoflammipi]

I live in an old house with a solid concrete floor that I know does not have a membrane underneath. I'm planning to do the kitchen out, and want to tile the floor. Under the exiting laminate I know there is some spalling of the concrete due to damp, so I need to deal with that too. Ideally I would like to insulate under the tiles before laying them, but from what I can find, the only commercial options are very thick (around an inch) or very expensive (around £30 psm). My initial intention was to dig out the spalling and repair, then paint the concrete with waterproofing paint (maybe bituminous??) before glueing and screwing 6mm ply to the floor and the tiling on that with a latex-added tile adhesive. Is there anything wrong with that? Any help or suggestions would be most appreciated. Note that money is definitely an object in this project, and I cannot raise the floor too much without disrupting the entire downstairs of my house or having my kitchen at a half-level!!

 

[mac391]

Tricky one when on a budget !! The correct way though, would be to repair any damaged/loose concrete. lay a liquid DPM (damp proof membrane) such as F-ball F76 (5kg covers 15m/2 for about £80). Then lay a 3mm screed on top giving one smooth, level and damp proof sub-floor.
insulation is expensive but marmox do a 10mm tile backing insulation board. just google marmox.