John Schmitt wrote:
Lobster wrote:

I'm about to lay a floor screed (approx 3m x 1.8m area) using a 3:1
mix of sharp sand:cement, using a mixer. I can easily come up
with the volume of wet mixture I need; but where can I find out the
number of bags of cement and sharp sand I need to pick up from
Wickes?!!

Sand has a bulk density of between 1.4 and 1.6 kg/l (T/m^3)As you are
making a mortar, the higher value will apply. The cement fills in
the interstices, so make no allowance for that or the water. Once you
have calculated how many kilos of sand, decide on your mix.
Calculating the cement should then be a doddle.

Thanks John, that's the sort of answer I was hoping for! The figure I
calculate is also close enough to the answer I came up with from t'other
John's pointer to the pavingexpert site to give me confidence I'm
ordering the right amount.

Out of interest, and for my possible future use, what's the rationale
behind the following:

Sand has a bulk density of between 1.4 and 1.6 kg/l (T/m^3)As you are
making a mortar, the higher value will apply.

Thanks
David