Different types of mortar

Types of Mortar

The best mortar for a particular job is not necessarily the strongest one. Other properties like workability, plasticity or faster hardening can be more important, though the strength of the mortar must of course be sufficient for the job. The Mortar should neither be much stronger or much weaker than the blocks with which it is used.

- Cement Mortar: This sets quickly and develops great strength. It is used in proportions of one part cement to three parts sand (1:3), which makes quite a strong and workable mix; down to a 1:2 mix, a lean mix which will be rather harsh and difficult to use.

- Lime Mortar: This is usually very workable and does not easily lose water to the blocks, but it is weaker than cement mortar and hardens slower. Lime mortars are nowadays largely replaced by cement mortars or combinations of lime and cement.

- Cement-Lime Mortar: This combines the properties of cement and lime to give a workable and strong mortar. The cement makes the mortar stronger, denser, and faster setting; while the lime makes the mortar workable and reduces the shrinkage during drying, because it retains the water better.

Batching

Before mortar can be mixed, the ingredients have to be measured in their correct proportions.

The ingredients can be measured by:

• Volume.

• Weight.

Mixing by Volume

Volume mixing can be carried out by hand or by machine, while weight mixing can only be carried out by machine.

Volume mixing by hand using a shovel

Materials calculated by volume should be accurately gauged or measured into the correct quantities for each specified mix. The crudest method is gauging the materials by the shovel-full. The amount on the shovel can vary according to the material, e.g. shovels of sand are often greater than shovels of aggregate.

Volume mixing by hand using a bucket

A slightly more accurate method is to use a bucket to measure the materials. As each bucket full is the same size, it will have the same volume.

Volume mixing by hand using a gauge box

This method is similar to using buckets, but wooden boxes are made to the correct volumes for the specified mix.

The boxes do not have bottoms and this allows the gauged material to fall through onto a board for shovelling into the mix.

Mortar volume batching

The first gauge box is placed on the ground and filled to the top with building sand and levelled off. The second box is placed on the top and filled to the top with cement and levelled off. The boxes are then lifted away to leave the materials in a heap ready for mixing.

Mixing by Weight

Traditional weight batching

By using a weight batch mixer, the weight of the aggregate is recorded as it is shovelled into the hopper. This is a more accurate method of batching materials than any of the previously described methods. The materials can be loaded into the hopper while the previously batched materials are being mixed. The weight of materials can be read on a dial by the operator who controls the weight, based on previous calculations for the constituent weights for the required mix.