Quantity of water in screed

[Tinago]

I want to put a water proofing admixture to my screed, but in order to purchase the right amount, i need to know roughly the volume of water to be added, assuming a 1:4 cement/ sand mix.

On another issue, my local building supply store gave me 400kg of cement for 2 m3 sand. This seems light to me - about half from what i can gather!! Should i be increasing this to a 1:4 or 1:3 mix

 

[noseall]

400kg's is not enough dust.

Adding water is not an exact process but you only want just enough to bind the mix together.

 

[ConcreteDrBill]

You want enough water so that the screed material can be formed into a ball in your hands without crumbling or letting water out