Properties of mortar

Mortar is a paste of binding material (cement, lime or mud), fine aggregate (sand) and water, used to join bricks or stones, and for plastering and pointing. A good mortar should have the following properties.

1. Workability: It should be easily mixed, spread, and applied without segregation; it should stay plastic long enough for placing.
2. Adhesion (bond strength): Good bond with bricks, stones and the surfaces.
3. Strength: Sufficient compressive strength to carry the load of masonry. Cement mortar 1:4 has 7 to 8 N/mm² at 28 days (IS 2250).
4. Durability: Resists weather, moisture, frost and chemicals.
5. Water retentivity: It should not lose water rapidly to dry bricks; this keeps the hydration complete.
6. Setting time and hardening: Initial set not before 30 minutes (cement); it should harden at a suitable rate.
7. Imperviousness: Low permeability so that water does not enter the wall.
8. Fire resistance.
9. Low shrinkage and cracking.
10. Economy, and good appearance of the joints.
11. Proper fineness of sand (graded, free of clay, silt, organic matter).