Set a clean wheelbarrow next to the wall. Once you mix the mortar you need to use it within the hour, so mix it near the worksite.
Fill the wheelbarrow halfway with two parts brickie's sand to one part Portland cement. Mix the two ingredients with a shovel.
Have a helper slowly begin pouring in drinking water. Drinking water is best because it lacks impurities that may weaken the mortar.
Stir the water into the cement and sand mixture with the shovel as the other person pours the water in. Continue adding water and stirring until the mortar has the consistency of a creamy paste. It is then ready for use capping the wall.