Mortar Strength Designations Explained

In masonry construction, mortars are classified based on their strength according to Indian Standards (IS codes), specifically IS: 2250 and IS: 1905. These classifications help determine the suitability of a mortar for different structural requirements. The designations use letters (H, M, L) to indicate strength levels and subscripts (1, 2) to denote variations within those levels.

Understanding Mortar Strength Categories

• H (High Strength): Represents mortars with the highest compressive strength.
• M (Medium Strength): Represents mortars with intermediate compressive strength.
• L (Low Strength): Represents mortars with the lowest compressive strength among these categories.

Strength Hierarchy in Mortar Designations

Within each strength category, the subscript indicates a specific strength level. Generally, the lower the subscript number, the higher the strength within that category. The standard hierarchy for decreasing strength is:

1. $H_1$: Highest strength within the High strength category.
2. $H_2$: Lower strength compared to $H_1$, but still within the High strength category.
3. $M_1$: Highest strength within the Medium strength category.
4. $M_2$: Lower strength compared to $M_1$, within the Medium strength category.
5. $L_1$: Highest strength within the Low strength category.
6. $L_2$: Lowest strength overall, within the Low strength category.

Determining Decreasing Order of Strength

Combining these categories and subscripts, the correct sequence representing the decreasing order of strength for the given mortar designations ($L_1, L_2, H_1, H_2, M_1, M_2$) is established by placing the highest strength category first and proceeding to the lowest, respecting the subscript order within each category.

Therefore, the decreasing order of strength is:

$H_1 > H_2 > M_1 > M_2 > L_1 > L_2$

This sequence aligns with the classifications defined in relevant IS codes for masonry mortars.