Replacing floating chipboard floor with concrete.

[adurling]

I currently have a floating chipboard floor consisting of damp proof membrane, polystyrene insulation, a clear plastic barrier and 22mm chipboard on top.

I am planning on laying 20sq m of polished granite tiles accross a kitchen / diner / utility / cloakroom and to avoid problems with cracking (and to avoid a step in the floor) I would like to concrete this area. I have a couple of questions tho...

The sub-floor seems to be of block and beam construction with a rough screed finish. Is this suitable for contreteing over?

I have about 70mm to play with - is this enough for insulation and concrete? If no room for instulation - how big a problem is it to have none?

Will the existing damp proof membrane be suitable?

Is this kind of area practical to do myself with a cement mixer and a shovel? Or should I get a man in?

Thanks for your help / opinions.

[thedoctor]

70mm is only thick enough for screed and whether or not you need insulation is down to you really. Having no insulation now should not be any different from having none in the first place. A sharp sand and cement screed vcan be laid at 4 to 1 mix but lay fairly dry and float over with a wooden oer pplyurethane float. You should be able to squeeze a lump of mixed screed in your hand and it should stay in one lump but no water should run out. Existing DPM should be fine