The message
from "paul" contains these words:

I am trying to mix the right quantities of sand, cement and lime to produce
a 5:1:1 mix. I have 25kg bags of cement and lime. The lime (hydrated) bags
are slightly bigger than the cement bags and I am having difficulties
getting the right quantities to mix.
Using a half bag of cement is approx 3-4 shovel loads and using a half bag
of lime I get approx 4-5 shovels but I expect will be lighter than the
cement since it is denser.
Ideally I would like to do this by the half bag to make the mix accurate.
How many shovels of the sand should I be using? Someone recommended 10
shovels to 1/2 bag of cement & 1/2 bag of lime but in volume (i.e. not
weight) this doesn't seem right to get a 5:1:1 mix.
Incidently I'm using a 100ltr electric mixer to mix it all up.

AFAIK quantities for mixing mortar have traditionally always been by
volume. While the actual ratio is probably not critical shovelfulls are
a pretty inaccurate way of measuring volume. FWIW I usually use 3 gallon
black plastic work buckets as a way of measuring volumes both for mortar
and concrete.

--
Roger Chapman