MORTAR
Mortar for Masonry
Mortar binds bricks and blocks together to give strength and stability to a wall.
Freshly mixed mortar must be soft plastic so that it spreads easily and makes good contact with the bricks during laying. It must harden thoroughly without becoming to strong. Too strong a mortar may cause cracking, is wasteful and is more expensive.
Technical information
Materials:
Cement
Use either:
Ordinary Portland cement (CEMI 42.5)
or Portland Cement CEMIIA 32.5
Ordinary Portland cement & lime
Lime
Use building lime with the SABS mark. Do not use quicklime or agricultural lime. Lime is sold in 25kg bags.
Lime should be used if the sand lacks fine material or is single sized as such sands tend to produce mortar with poor workability unless lime is included in the mix.
Lime also helps the fresh mortar to retain water when it is placed against dry cement brick or block and helps to prevent cracking of the hardened mortar.
Sand
The sand should be clean (grass, leaves, roots etc, are harmful) and it should not contain too much clay. It should consist of hard particles which range in size from dust up to about 2mm. Pit sands generally have these characteristics. River, dune and beach sands are often too uniform in size (single sized) to give good results.
Ready-mix mortar (dry)
In some areas mortar can be bought in bags ready for mixing and use. It should be used in accordance with the manufacturer’s instructions.
Batching the materials
A builders wheelbarrow is a convenient measure for large batches; the capacity is 65 litres. Steel drums of 20 or 25 litre capacity and buckets are useful for small batches. Check the capacity of drums and buckets when filled to the brim as this is often more than the nominal capacity. To batch, shovel material into the measure and then strike off, level with the brim.
Mixing
Mixing should be done on a clean hard surface such as a smooth concrete floor or a steel sheet. Small batches may be mixed in a wheelbarrow as the volume of the batch is no more than half the capacity of the barrow.
Sand, cement and lime, if used, should be mixed until the colour of the mix is uniform. Then add water in small quantities, mixing after each increment, until the mix is soft and plastic.
Handling
If mortar is left in the sun before being used, it should be covered with plastic sheeting or a wet sack. Discard mortar that has been stiffened so much that it is impossible to remix it without adding more water.
Note: Concrete bricks and blocks should not be wetted before being laid. Burnt clay bricks should be wetted before being laid.
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