Water/cement ratio
The less water in your concrete mix the stronger it will be. The more water you add the more dilute the mix is. When the mix is diluted the cement particles are too far away from each other to form strong bonds. for more info on concrete curing click here.

Example: A W/C of 0.4 means that for every 1Kg of cement in the mix you add 0.4L of water

The temptation is to keep adding more water to the mix because the more you add the easier the mix is to work with - it’s less effort to mix, pour and trowel. However, this compromises the strength and longevity of the final product. When the water content is too high this gives you crumbly powdery concrete which will be terrible to skate and will not last long. It also causes problems when making quarter pipes and flat banks as it does not hold its shape and slumps down to the bottom of the form.

Figure 2 shows how strength decreases with an increase in w/c. Use the minimum amount of water you can in the mix.

Water addition per 25kg of cement in the mix - every 1.25L of water increases the W/C by 0.05

W/C Water (Litres)
0.20 5
0.25 6.25
0.30 7.5
0.35 8.75
0.40 10
0.45 11.25
0.50 12.5