Mortar is the material used to bind two masonry units together. Although sometimes confusing, it is important to choose the correct type of mortar for a construction project. While all mortars should be resistant to water penetration, mortar mixtures will vary in strength, adhesion and flexibility.

The compressive strength of mortar is measured in pounds per square inch (PSI). It is generally accepted that the stronger the mortar, the better. However, if the mortar installed is stronger than the masonry, this can lead to spalling and cracking of the softer masonry.

HPMC is widely used in drymix mortar industry. Could be soluble in water and form the transparent solution. As the important additives in mortar, Hydroxyproypl methyl Cellulose could increase the water retention, increase the workability and increase open time etc.

HPMC      

Bonding is the ability of mortar to adhere to its applied units. Good bonding is required when laying foundations; however, this is not the case when re-pointing to structurally sound walls. Highly bonded mortars are likely to stain the surface of the wall, resulting in an undesirable aesthetic appearance.

Flexibility may be an important factor in determining the correct mortar mix. This mortar characteristic, called flexibility, allows the structure to move. A flexible mortar with a higher concentration of lime may be a better choice for repair work in high-rise buildings. Stronger cement mortars will not be able to withstand the swaying or expansion and contraction of higher structures. Finding the right balance between strength and flexibility is essential when choosing the right type of mortar for the job.

All conventional mortars are essentially a mixture of sand, Portland cement and slaked lime. These three ingredients are mixed in different proportions depending on the intended use. The four main mortar types most commonly used are: N, M, S and O types.

Type N is the most common type of mortar and is usually recommended for external, above-ground walls. This universal mortar has good bonding capacity. With a compressive strength of approximately 750 PSI, Type N mortar is ideal for use in semi-soft stone or masonry applications. It is more flexible than high strength mortars and helps to prevent cracking and spalling of adjacent masonry units. Although typically used for bricklaying, Type N can also be used to reposition newer brickwork.

For Drymix Mortar

Type M mortar is the strongest of the four, with a compressive strength of 2500 PSI and should be used when structures must be subjected to high gravity and/or lateral loads. type M mortar is also a good choice for hard stone work where the compressive strength of the stone is greater than 2500 PSI. the properties of type M mortar make it ideal for underground applications, such as foundations and retaining walls.

Type S mortar is a medium strength mortar with a compressive strength of approximately 1800 PSI. type S mortar can be used for external walls of the same grade/ or below grade, as well as traditional mortar system hardcoats. type S mortar has greater strength and bonding properties than type N. The increased amount of lime in type S mortar allows the mortar to withstand excess moisture and increases its bonding and elasticity capabilities.

Type O mortar has the weakest compressive strength at approximately 350 PSI. type O is easy to apply and the consistency of the mix makes it ideal for repositioning on structurally stable walls. Its low compressive strength makes it ideal for soft stone applications such as inlaid sandstone or brown sandstone. type O mortar also allows for more flexure, which helps to prevent cracking and spalling of masonry units.

Although there are other scientifically modified cement mixes, these four types are the most commonly used forms of mortar. In order to select the correct one, it is important to thoroughly understand the structural requirements of the project. If in doubt as to which type of mortar should be used, building owners and contractors should consult a structural engineer.

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