Question

how do we determine mortar mix proportion in masonry work

Answer 1

Mortar mix proportion i.e. fixing proportions of cement and sand in mortar offers uniformity in the field performance and durability of masonry construction. Appropriate proportioning of mortar constituents assistances in achieving the subsequent benefits:

• Regularity of strength
• Unvarying workability
• Even colour
• Homogeneity of proportions and produces good quality mortar

Mostly fixing the proportions of the ingredients of mortar i.e., cement and sand are accompanied by volume proportioning in preference to proportioning by weight.

Table showing proportions of ingredients of mortar as per ASTM:

Proportions by Volume Mortar Type Portland Cement Lime Sand M 1 14 3% S 1 1 12 4% N 1 1 6 O 1 1 2 9 K 1 1 3 12

Considerations for Mortar Mix Proportion

Superior attention must be paid throughout the measurement of sand, as disparities happen by the occurrence of humidity contented in sand. The moistness existing in the sand will effect in the phenomenon called bulking of the sand. In comparison to dry sand, the moist sand will have increased volume resulting in fault in measurement of quantity. This variation in mixture quantity will adversely and negatively affect the strength and the bonding properties of the mortar.

A mortar mix with sand in excess quantity will cause in a tough and non workable mix resulting a fragile bond. Such types of mortar are prone to act worse for the period of freeze and thaw situations.

In comparison concrete the workability of mortar is higher. This is due to the phenomenon that masonry units absorb water to some extent this will decrease the water-cement ratio in the mortar mix which will result in the strength and binding properties.

For obtaining a proper Mortar Mix

A proper mortar mix should possess the following properties:

• Mortar should spread easily
• Must possess good workability
• Mortar must easily fill into the joints
• Allow easy positioning of the unit to level and plumb line
• It must stick to the vertical surfaces without spilling