well you cant lay sand and cement 5mm thick. Way to thin and will fail in no time at all. As for the moister bit, you could just rely on the dpm underlay but it is not a British standard. It is on your back with what you decide. As for your local shops who recommend that a moister test was not need and said use sand an cement. Well this is really really bad advice! Could you email there names and area they are in to me please! ( Think they need a little visit )
If you want to raise floor 10mm and there might be damp you need-
Green bag with either 55 acrylic liquid or 114 latex liquid. ( i would suggest you use acrylic) You also need to fill the mix! Chipping etc (aggregate) added to the compound while mixing, ask your supplier for these when you purchase the compound. Prime the floor with 131 primer.
Or you could use 600 deep section compound.
Remember tho that if there is a moister problem that you will have no product garentee.
If you want to raise floor 10mm and there might be damp you need-
Green bag with either 55 acrylic liquid or 114 latex liquid. ( i would suggest you use acrylic) You also need to fill the mix! Chipping etc (aggregate) added to the compound while mixing, ask your supplier for these when you purchase the compound. Prime the floor with 131 primer.
Or you could use 600 deep section compound.
Remember tho that if there is a moister problem that you will have no product garentee.