floor slab with damp proof membrane on surface?

[Saycheese5]

So in my case shall I remove it and replace with something else to level the floor? i'm trying to understand why you can apply a screed of between 1mm and 6mm using self levelling compound but not a sreed of the same thicknees using premixed sand/cement mortar (very fine sand)? Unfortunately the self levelling compound has not worked for me because I can get a lot of sun in that room and eventually the heat from the direct sunlight has cracked it twice.

 

[mointainwalker]

i'm trying to understand why you can apply a screed of between 1mm and 6mm using self levelling compound but not a sreed of the same thicknees using premixed sand/cement mortar (very fine sand)?

All the following is speculation because my chemistry/physics knowledge didn't go that way and I would be happy to be corrected..

SLC is only extremely fine cement particles - I guess 0.1 mm or less - and through whatever chemistry many many layers of particles bond to make a durable surface.

Mortar is completely different because you will have pieces of gravel up to 4 or 5 mm in one stone ( unless you sieve it or pay a lot of money for silver sand ). This one stone is then the thickness of your total "screed" layer.

It will inevitably be dragged by footsteps and since it is one large lump it will be pulled out of the screed. This then weakens the integrity of the screed as well as this bit of gravel potentially laying there and then being ground back into - and breaking up - what's left.

 

[browfish]

How did this get onto a debate on the minimum thickness of screed possible.
Has anyone ever come across a hardcore layer of flint pebbles as a natural dpc layer as this is what i assume i have

 

[mointainwalker]

When I was renovating my stable, I was astonished to find - after lifting the flagstones - that they were laid on a bed of flat stones which were bedded on their ends ( clear I hope ? )

At the time I thought it was just the usual massive over-engineering that I had found elsewhere in the barn ( C18) but I suppose it could have been intended as a damp-proofing measure. Not flint because there isn't any around here.