foundation system of burj al arab

Foundation design

What is the Significance of Modulus of Subgrade Reaction of Soil?

Contact Pressure Distribution Beneath Footing

How to Determine A Foundation Whether to be Designed as Flexible or Rigid Body

Concrete Properties

Concrete Roof and Floor Surfaces

Relation Between Compressive and Tensile Strength of Concrete

Quality of water in concrete Mix

Storage of Cement


What is Mortar? Specifications for Mortar

Mortar is a cementitious material used to bind building blocks like bricks, stones, concrete masonry units, connectors and sometimes reinforcement (for reinforced masonry) together to render strength and resistance to weathering. Mortar fills the gaps and seals irregularities between them. Mortar may be of asphalt, pitch, clay or soft mud (for mud bricks) except conventional cement and lime mortar. Mortar is used in civil construction to achieve number of purposes. The principal functions of conventional mortar are as follows:
  • To provide level bedding upon which building stones or blocks are placed and permit course levels considering small variations into unit height.

  • To transfer compression loads 

  • To hold building blocks together by bonding them to form a wall which will offer a resistance to shear and tensile forces (often called bond strength). It is important that building units placed at the top of wall must not be dislodged easily.
Masonry mortar is the key material for masonry construction and its quality is essential to have expected structural performance and good workmanship. In basic word, mortar is required to lay block or brick. The requirements of ideal mortar is related to expected basic function of it both during construction and while life cycle of masonry assemblage. The desirable properties of mortar as follows:

Workability and stiffening time

Mortar is evaluated depending on

  • Its spreadability i.e. body and flow

  • Ability to adhere to surface (adhesion to vertical surface)

  • Stiffening time (also known as board life); the duration throughout which mortar retains workability irrespective of ambient conditions prevails at construction site.

Plasticizers, if added any, included in mortar not only to contribute to yield better workability, but also improve stiffening time. Mortar should be readily extruded from joints when masonry units are placed but must not smear or drop. Stiffening time together with optimum workability indicate its compatibility in respect of plasticity to be worked properly with masonry units and keeping suitable condition for application.

Workability and stiffening time are generally correlated with other properties of mortar like

• Water retention
• Consistency retention
• Air content

Workability and stiffening time are often overlooked during selection of constituent materials and mortar type. But their importance is indisputable when one takes into account the critical role of the workmanship to achieve a properly finished wall. Each of the plastic characteristics of mortar have an evident impact on hardened properties and performance of mortar. In one word, workability is the evaluation of mason about the ability of mortar to cling to joints, slide smoothly from the trowel and provide uniform support to masonry units.

Strength and durability

Bond is one of the most important physical properties at hardened state of mortar which is considered less predictable and inconsistent in nature. There are various factors that affect bond strength of mortar; both strength and durability parameters have to be considered. An intimate and thorough contact between masonry block and mortar is essential to produce good bond; ASTM C270 provides us a mortar cement specification which includes bond strength criteria. The procedure to determine conformance criteria of mortar cement included elimination of, as much as possible, effect of workmanship, properties of masonry units, curing on evaluated bond strength.

As cement compound exist in the mix reacts with the water, the masonry mortar gain its strength and becomes harder gradually with time. The mortar placed in between masonry units must interact with them to produce an assemblage that comply with the structural and service requirements. The behaviors of hardened mortar influences strength and durability which include

• Compressive strength

• Bond with units

• Shrinkage

• Water absorption

• Resistance to deterioration due to freezing and thawing

• Elasticity

• Resistance against sulfate attack 


Sometimes construction type is selected based primarily on visual appearance of masonry. Based on the requirement, the expected appearance of mortar may be blended with selected color of masonry blocks or may have contrast with units. Factors influencing the appearance of joints finished by mortar included: 

  • Selection materials: The color of constituent materials of mortar like sand, mortar cement, masonry cement, lime or Portland cement mainly influences the appearance of joints. Sometimes expected pigments can be included in the mortar mix to achieve desired color.The colored mortar can be produced by

  • Using color ingredients that are available in the market as colored form like including colored cement  
  • Adding pigments to the mix of natural or normal ingredients at the construction site.

Texture of joint surface

The surface texture of joint and it is appearance are achieved by 

• Proper gradation of sand
• Right consistency of mortar during tooling 
• Jointer type used while tooling joints 
• Proper clearing operation

Selection of type of mortar:

Proportion and manufacturing method of mortar are selected to achieve expected properties as supplied to the producer. They are classified based on their compressive strength and specified mortar is produced on the basis of predefined proportions; the properties of resulting mortar are believed to conform product specifications. It is not easy to define a portion that will yield desire strength and durability properties. ASTM C270, ASTM C780 and ASTM C91 provided necessary guidance for production of mortar. Except strength, other properties of mortar are also important. Only one criterion cannot be taken as selection criteria, as an example consider high strength mortar which alone cannot produce a quality masonry assemblage as poor workability, reduced stiffening time and essentially elasticity usually related to higher strength. Thus a low quality mortar will result poor workmanship at early stage and less serviceable as finished masonry. 

A non-air entrained mix may improve bond strength early age but may decrease workability and durability like deterioration to freezing and thawing cycle.