Mortar Specifications and Mix Types

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Questions and Answers

What is the maximum allowable lime content in Class I mortar when using common cements?

  • Up to 25 kg
  • None
  • No limit specified
  • Up to 10 kg (correct)

Under what condition can the types of sand and cement in a strength mortar be altered during construction?

  • Only when directed by the architect
  • If the alteration is cost-effective
  • If tests show required strength can be achieved (correct)
  • If it is more readily available

What method should be used for measuring materials for mortar to ensure consistent proportions?

  • Weight batching of one material only
  • Volume batching of all materials
  • Weight batching of all constituent materials (correct)
  • A combination of volume and weight batching

What is the correct amount of cement required for 2 standard wheelbarrows of Class I mortar using common cements?

<p>50 kg (B)</p> Signup and view all the answers

Which type of cement is not permitted to have lime added in Class II mortar?

<p>Both B and C (D)</p> Signup and view all the answers

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Study Notes

Mortar Specifications

  • No mortar plasticizers or set-retarding admixtures should be introduced unless specifically allowed.
  • Changes to sand and cement types in strength mortar are permitted only if tests confirm the desired strength.
  • Consistent control over material proportions for mortar mix is essential during measurement and construction.

Prescribed-Mix Mortar

  • Mortar mix proportions are outlined in Table 7.
  • Class I Mortar:
    • Common cements: 50 kg cement, 0-10 kg lime, max. aggregate size of 130 mm, equivalent to 2 standard wheelbarrows.
    • Masonry cements (MC 22.5 X, MC 12.5): 50 kg cement, no lime, max. aggregate size of 80 mm, equivalent to 1 standard wheelbarrow.
  • Class II Mortar:
    • Common cements: 50 kg cement, 0-25 kg lime, max. aggregate size of 200 mm, equivalent to 3 standard wheelbarrows.
    • Masonry cements (MC 22.5 X, MC 12.5): 50 kg cement, no lime, max. aggregate size of 130 mm, equivalent to 2 standard wheelbarrows.

Cement Measurement Guidelines

  • Cement should always be measured by weight, not volume.
  • A factory-packed 50 kg bag of common cement occupies approximately 33 L but may increase by up to 20% in bulk when poured, affecting measurement accuracy.
  • It is recommended to use whole bags for volume batching due to variances in bulk density.

Lime Usage

  • The use of lime with common cements is permitted within the specified maximum limits but cannot substitute for cement in the mix.

Wheelbarrow Specifications

  • A standard wheelbarrow, conforming to SANS 795 (type 2), has a capacity ranging from 60 L to 70 L.

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