Types of mortar

Mortar is one of the oldest building materials, enabling large structures to be constructed from small, easy-to-handle components. It was used by the Romans, Greeks and Egyptians, and the oldest example may date back as far as 10,000 years in Israel (ref. Mortar Industry Association).

It is composed from a mixture of a fine aggregate, a binder and water which creates a paste used in masonry construction as a bedding and adhesive to bind and fill the gaps between adjacent blocks of brick, concrete or stone. There are many different types of mortar that are used in building construction.

Mortars can be categorised based on the type of application they will be used for:

• Bricklaying or stone-laying mortar: This type of mortar is used to bond together stones or bricks.
• Finishing mortar: This type of mortar is used for pointing and plastering works.

Mortar can also be categorised according to the type of binding material that is used, as this, along with quantities, will determine the quality and strength of the mortar:

• Cement mortar: The binder is cement and the fine aggregate is typically sand (ratio of 1:2 – 1:6). This provides good strength and water resistance.
• Aerated cement mortar: Air-entraining agents are added to cement mortar to increase its plasticity and workability.
• Lime mortar: The binder is lime, which is more ‘breathable’ than cement mortar, meaning that it is less likely to trap moisture within the construction.
• Gypsum mortar: The binder is plaster. This type of mortar has low durability in damp conditions.
• Gauged mortar: A composite of lime, cement and sand, which combines the plasticity of lime with the strength of cement.
• Surkhi mortar: The binder is lime and the fine aggregate is surkhi (finely-powdered burnt clay). This provides more strength than sand.

Another way of categorising different types of mortar is based on their bulk density in a dry state. These include:

• Heavy mortar: Bulk density of 15 kN/m3 or more. Typically, heavy quartzes are added as adulterants.
• Lightweight mortar: Bulk density of less than 15 kN/m3. Typically, light porous and soft sands are added as adulterants.

There are also several special purpose mortars, including:

• Fire resistant mortar: Aluminous cement is mixed with the fine powder of fire bricks to create a mortar which can be used to act as a fireproofing agent.
• Sound absorbent mortar: Binders can be cement, lime, gypsum and slag, with pumice and cinders as adulterants, to create a sound-insulating layer.
• X-ray shielding mortar: Heavy mortar with a bulk density of approximately 22 kN/m3 used to protect against X-rays.
• Chemical resistant mortar: Additives can resist chemical attack.

Mortar is typically supplied in two different forms:

• Wet ready-to-use mortar that requires no further mixing.
• Dry ready-to-use mortar which requires the addition of water.

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[edit] Related articles on Designing Buildings Wiki

• Aggregate.
• Binding agent.
• Cement.
• Grout.
• Hot-mixed mortars: the new lime revival.
• Lime mortar.
• Mastic sealant.
• Mortar.
• Mortar analysis for specifiers.
• Pointing.
• Portland cement.
• Rendering.