Detailed specification of cement sand mortar 1:4

Detailed specification: cement sand mortar 1:4

Scope: Preparation of cement sand mortar in the proportion of 1 part cement to 4 parts sand by volume, for use in brickwork, plastering and other work.

Materials

• Cement: OPC 43 grade/PPC conforming to the relevant Nepal Standard/IS; fresh, free from lumps, stored in a dry shed on a raised platform and used in order of delivery.
• Sand: clean, hard, well-graded river or pit sand, free from clay, silt (< 4%), mica, salts and organic matter; fineness modulus 1.5–2.5 (for plastering, finer sand of FM about 1.0–1.5, passing a 2.36 mm sieve).
• Water: clean, potable, free from oil, acid, alkali and organic matter.

Proportion: 1 : 4 by volume. One 50 kg bag of cement is taken as 0.035 m³, and sand is measured in a gauge box. For about 1 m³ of mortar, around 8–9 bags of cement and 1.15–1.2 m³ of sand are required (indicative).

Mixing

• By mixer: dry mix until uniform, then add water for the required consistency, and mix for at least 2 minutes.
• By hand: on a clean watertight platform; mix the dry sand and cement until the colour is uniform, then add water gradually and turn the mix over at least three times.
• Use only the minimum water necessary for a workable mix.

Use: Mortar must be used within 30 minutes of adding water; if it starts setting it must be discarded; no re-tempering.

Testing: The 28-day compressive strength of 70.6 mm cubes (about 7–10 N/mm²) may be checked as the engineer instructs.

Measurement and payment: Measured by volume (m³) when paid separately; otherwise included in the rate of the item in which it is used.