Today, we ordered 13 tons of 10mm gravel and sharp sand ballast. This is the
quantity we think we need to make the concrete to fill up all the columns in
our hollow blocks we have been building the walls with.
Each “column” will need about 18 to 20 litres of concrete, depending on
whether it is 5 blocks high or 6. We can mix a medium sized load in the
mixer using a half bag of cement and 40 litres of the ballast.