Q.: I have a residential-concrete specification that calls for a 1:2:4 concrete mix. What does that mean?
A.: This is a little-used method for showing the amount of cement, sand, and coarse aggregate in the concrete. The specification should also say if those proportions are by weight or volume.
If the proportions are based on weight, use 4 pounds of coarse aggregate and 2 pounds of sand for every pound of cement. To make the concrete, though, you still need to know the required water-cement ratio.
If the proportions are based on volume, use four shovelfuls of coarse aggregate and two shovelfuls of sand for every shovelful of cement. Batching by volume isn't very accurate because a shovelful of dry sand will put more sand in the mix than a shovelful of wet sand.