•Explain the main functions of a good mortar mix

• State how good workmanship will improve the sealing properties of a mix

• Calculate mortar quantities for walling areas

Lesson Objectives

Mortars Generally

Mortar fulfills a number of functions. These include:It cements the bricks together to provide stability - and solidity, while holding them apart to spread loads evenly.

It compensates for irregularity between units when straight, level and plumb walling is laid. It also seals any gaps to resist wind or rain penetration.

As well as its gap-filling adhesive function it is required to have durability and strength to suit the application. It also contributes to the aesthetic qualities of the wall.

Three important Functions

Mortars should have:1. good workability 2. sufficient resilience to accommodate long term thermal

movement of the masonry 3. adequate bond strength 4. good resistance to water penetration

Mortar is made from fine aggregate (usually sand) and a binding agent (nowadays usually cement). When mixed with water a chemical reaction, called hydration, occurs and the mortar sets. Early mortars were usually based on lime and sand but they were very slow to set and readily absorbed rain water (the mortar set through a process known as carbonation where the lime gradually hardened by absorbing carbon dioxide from the atmosphere).

Mixing On Site

Requirements of a Good MortarRequirements of a Good Mortar

• Adequate compressive strength

• Adequate bond strength

• Durability:- resistance to frost and chemical attack

•Joints sealed against, wind driven rain

LONG LIFE REQUIREMENTS WORKABILITY

Bricklayers require a “fatty” mortar which hangs on the trowel without being sticky, spreads easily and stiffens neither too quickly nor too slowly.

Modern mortars use cement as the main binding agent although hydrated lime (ie bagged lime) is often introduced into the mix to give it a more plastic feel and to make it more ‘workable’.

Lime also improves the mortar’s ability to cope with thermal and moisture movement.

Mixed Ready for Use