Cement mortar is an intimate mixture of cement , sand and water. Cement is the binding material, and sand is the fine aggregrate. The binding material (cement) develops when water is added to the mixture. Sand suitable for cement mortar include, river sand, gutter or pit sand.
Sand used for cement mortar must have the following properties;
- should be chemically inert.
- It should be free from organic or vegetable matter.
- Should not contain salt.
- Should contain sharp, angular, coarse grain that is well graded and hard.
Preparing cement mortar.
Cement and sand in the required ratio is first thoroughly mixed in dry condition then water gradually added and mixed until required consistency is achieved.
Cement to sand ratio for various works;
- Masonry Works : 1:6 to 1: 8
- Plastering: 1:3 to 1:6
Curing is the process of ensuring sufficient moisture during hardening of mortar. Curing is ensured by spraying of water. It starts 6 – 24 hours after mortar has been applied
Characteristics of Cement Mortar;
- Cement sand ratio mix richer than 1:3 is prone to shrinkage.
- Mortar with well-proportioned mix gives an impervious surface.
- Mortar with leaner mix may become porous.
- Strength of mortar depends on the cement sand ratio.
Compressive Strength of various cement sand ratios;
- 1:3 – 10N/mm2
- 1:4 – 7.5N/mm2
- 1:5 – 5.0 N/mm2
- 1:6 – 3.0 N/mm2
- 1:8 – 0.7 N/mm2
Uses of cement mortar.
- To bind masonry units like blocks and bricks.
- Plaster walls and slab.
- Give neat finishes to walls and concrete works.
- Fill joints and cracks in walls.
- As filler material in stone masonry.