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Mortar: what materials do I need?
Cements for use in mortar should be common cements complying with SABS EN 197-1 and masonry cements complying with SABS ENC 413-1.
CEM 1 32,5 (ordinary portland cement) and CEM 11/A (S, V or W) 32,5 (portland cement 15) may be used in mortar. It is not advisable to use CEM 111/A 32,5 (PBFC).
Unless the mortar sands are good quality, mortar with common cement lacks plasticity, may bleed and will be harsh to work with. This deficiency in properties may be overcome by using masonry cement. The use of lime in mortar mixes is beneficial but is difficult to obtain. Masonry cements are readily available.
Sand for mortar should comply with SABS 1090 and be well graded from 5mm downwards.
Sand should be evenly graded and should not contain excessive dust or other fine material. The use of fine sands of more or less uniform particle size, though contributing to workability, frequently leads to excessive shrinkage and cracking of the joints. Sands containing high percentages of clay tend to give a conveniently plastic mix, but also lead to undue shrinkage.
- Crusher sand, because of the shape of the particles (broken edges) yields a rather harsh concrete, but it is fairly consistent and contains no clay
- River sand is generally clean and free from clay, the rounded particles pack together easily for good workability
- Pit sand contains excessive proportions of clay, but may be well graded otherwise. This is therefore not fit for concrete work.
- Beach or sea sand must be washed. Unwashed beach sand must not be used for mortars as its high cloride content will corrode steel reinforcement and cause excessive efflorescence.
- Dune sand is generally clean but poorly graded
- Mine dump sand is generally unsuitable because it is too fine and may be contaminated with harmful chemicals.
The addition of lime to mortars is a highly desirable and recommended practice and building limes complying with SABS 523 are available from builders merchants. Lime imparts the properties of plasticity and water retention to mortar. The latter property is important as it prevents mortar drying out, resulting in the incomplete hydration of the common cement.
Lime used in mortar is hydrated lime (commercial bedding lime) and not quicklime or agricultural lime. Lime give the best results when used with coarse sands. Lime with clayey sands can make the mortar over-cohesive and difficult to use. Lime should not be used with masonry cement.