MIXING MORTAR

Mixing Water

The essential criterion for mixing water is that the water should be clean, as any impurities will affect the strength of the finished mortar or result in staining. The term ‘drinkable’ (or ‘potable’) is often used to define the quality of clean and uncontaminated water fit for use in mortar.

Подпись: Gauging of Mortar Mix Materials In this context, ‘gauging’ is the term used to describe the measuring out of quantities of individual dry materials for a mortar mix. It is common practice on construction projects simply to load a mixer using a shovel, meaning there is no accurate control over the proportions of materials. This is, however, bad practice and the only way to achieve a degree of accuracy is to use batching by weight or by volume. The principles are the same as those applied when measuring out materials for concrete mixes. For more on the importance of good storage arrangements, grading of aggregates and gauging of materials, see Chapter 2.

Mortar sets as a result of the hydration process that takes place between the water and cement, which makes the cement set hard and binds the sand particles together. Only a small amount of water is actually required for the hydration process to take place, but enough water must be added to make the mortar workable. This will always exceed the amount needed for hydration of cement. In essence, water is added until the mix ‘feels right’ and meets the workability requirements of the bricklayer.

In reality, a typical cement-lime-sand mix of 1:1:6 will require approximately 7 litres of water for every 5kg of
cement. A vastly excessive amount of water produces an overly workable mix, can lighten the colour of the finished mortar and result in a weakened mortar mix.

Due to the amount of water that is present, mixed mortar will be usable for a few hours, depending on weather conditions. When it does start to ‘go off’ it can be ‘knocked up’ by adding more water, but this is not good practice as the mortar will have begun to set by hydration and will already have attained some of its initial strength. Re-used mortar and re-diluted cement paste will not achieve the original strength capability when they finally set.

Typical Cement-Lime-Sand Mortar Mixes

Engineering Bricks and Bricks and Lightweight

bricks and blocks, average blocks, average blocks in

dense concrete strength. Below strength. Above internal

blocks DPC DPC walls

1:%:3 1:1:6 1:2:8 1:3:10