What is the best way to gauge and mix mortars?
When the appropriate mix has been chosen, the materials should be carefully gauged. Weigh-batching gives the most accurate form of gauging. If the materials are to be measured by volume then gauge boxes or other containers should be used for each of the materials.
Measuring by shovel is not recommended. Sand is normally damp and cohesive, and will stand up on the shovel, whereas cement, being a dry and fine powder, will fall off the shovel. Mixes measured by volume in this way would be deficient in cement.
Variability in mix proportions is also likely to affect colour, strength and durability.
Mechanical mixing, using for example, small tilting drum mixers, produces good results and is preferred to hand mixing. When all the materials are in the mixer a mixing time of 3 to 5 minutes is generally satisfactory. Short mixing times can lead to poor uniformity and workability. Long mixing times can lead to excessive air-entrainment with plasticised mortar. When mixing by hand, the materials should be thoroughly mixed in the dry state (turn over at least 3 times) to obtain uniformity and consistency before adding water.