Thanks Tomfe -
So if I can get sand which is similar, will the cement need to be white (e.g snowcrete) to avoid 'greying' the mix? Will it then just be the ratios I need to alter for the 'test mixes', e.g 3:1, 4:1 & 5:1 (or somewhere in between)?
Sorry I'm a complete newbie when it comes to...