If you have driven around your neighborhood and looked at the buildings or walked up a set of brick steps, chances are very likely you have seen mortar.. But as civil engineers we often find ourselves having to take a closer look at mortar. First though, what exactly is mortar? Mortar is made of cement, sand, lime, and water and is used as a glue to hold bricks, blocks, stone, and other masonry products together. The cement in a mortar mixture is the ingredient that sets and hardens when it interacts with water. It is also important to note that mortar is different from concrete. Concrete is made of sand, cement, lime, gravel, and water. Concrete’s more flexible nature allows it to be formed into molds for a variety of applications such as buildings, foundation slabs, footers, patios, and concrete masonry products (think cinder blocks) before it hardens to be rock solid.
The mortar itself has a long history. The earliest form of mortar was a basic mixture of mud and clay used in primitive buildings and structures in Jericho in the 10th Century BCE. Mortar in the form, as we know it today, was invented in 1794 by Joseph Aspdin, an English cement manufacturer, who went on to patent “ordinary Portland cement mortar” in 1824. Efforts in the construction continued to further develop mortar, mainly focusing on increasing its strength, and in 1930, ordinary Portland cement mortar replaced lime mortar cement as the common mortar-type construction material.
Mortar is a workable paste that bonds brick, concrete block, or other masonry products together. Mortar provides structural stability to a wall and overall structure, but it is weaker than brick and is a sacrificial element in the structure giving way to cracking and settlement, because it is easier to repair than the brick or other masonry products it bonds together.
Sounds pretty simple so far, right? Well, there are 4 different types of mortar: Type M, Type N, Type O, and Type S. Each mortar type is dependent on the ratio of cement, lime, and sand used and the different ratios of these materials give mortar different characteristics such as flexibility, bonding properties,, and compressive strength. A project’s design specifications will specify the type of mortar to be used for a particular project based on structural needs, site characteristics, location, and climate.
Type M
Type M Mortar is commonly used for applications involving heavy loads and below-grade applications, such as retaining walls, and driveways. Although Type M mortar has a minimum compressive strength of 2,500 psi of compressive strength, it has poor adhesion and sealing properties, so it is unsuitable for many exterior applications and uses. However, Type M is often used with natural stone because it offers similar strength to that of stone.
Type N
Type N Mortar is a general-purpose mortar and is commonly used in above-grade, exterior, and interior applications. The ratio of Type N mortar consists of 6 parts sand, 1 part lime, and 1 part Portland cement. Type N mortar has a 28-day compressive strength of 750 pounds per square inch (psi)
Type O
Type O mortar has low compressive strength and, as such, is recommended for interior, above-grade applications, and non-load-bearing walls. It may have some very limited exterior use applications such as repointing masonry, but this may not be the best choice of mortar for those repointing projects. Most importantly, due to its low compressive strength, Type O mortar is NOT recommended for areas with high winds. Type O mortar has a 28-day compressive strength of 350 psi.
A portion of the masonry work of this chimney has been repointed. Photo courtesy of Deposit Photos.
Type S
Type S Mortar has a high compressive strength, its minimum compressive strength is 1800 psi and different ratios of ingredients can be proportioned to obtain 2300 – 3000 psi compressive strength. Due to its high compressive strength, Type S mortar is commonly used for projects at or below grade, such as masonry foundations, manholes, retaining walls, patios, and sidewalks, this is because it is able to withstand soil pressure, wind, and seismic loads.
An example of a brick manhole under construction. Since this application is a subgrade, it is likely that Type S Mortar is being used. Photo courtesy of Deposit Photos.
Type K
There is also a fifth type of mortar, Type K, that we often don't include because it is not used in new construction. However, Type K mortar has a very low compressive strength of 75 psi. As such, it is very soft and used in masonry restoration projects and applications on historic or ancient buildings.
Choosing the right type of mortar is essential to the safety, success, and longevity of any construction project. The specific type of Mozart to be used should be decided after a thorough analysis by a licensed structural engineer.
Speaking of licensed engineers, We are here at Civil Engineering Academy to help you every step of the way towards becoming a licensed PE – acing both those FE and PE Exams! These courses were the keys to success on my journey and I invite you to check time out and Check out Civil Engineering Academy Breadth and Depth Courses. We’ll see you there!
Do you have a topic or interesting project that you would like us to cover in a future blog post? Submit it to us here. We would love to hear from you!
________________________________________________
Author: Matt Fanghella, PE, CFM
CEA Resources:
The Ultimate Civil FE Review Course – https://civilfereviewcourse.com
The Ultimate Civil PE Review Course – https://civilpereviewcourse.com
FE and PE Practice Exams – https://civilengineeringacademy.com/exams
Free Facebook Community – https://ceacommunity.com
YouTube Channel – https://www.youtube.com/channel/UCPeFLBZ2gk0uO5M9uE2zj0Q
Newsletter – https://civilengineeringacademy.com/newsletter
Instagram – https://www.instagram.com/theceacademy
Twitter – https://twitter.com/civilengacad
Reach out to Isaac – [email protected]