Whether you’re working on a professional jobsite or at home on a DIY project, few bonding agents are as versatile and as essential as mortar. But despite its versatility and wide-spread use, all mortar is not the same. It’s also not the same as concrete or grout, for example.
As it turns out, there are many different ways to combine mortar’s essential ingredients. In other words, there are different mortar mix ratios. Each of these variations comes with different properties, making them ideal for use in different types of projects. Some variations are better for use above grade or below grade, while others are limited in their ability to bear weight.
In this guide, you’ll learn about what the most common types of mortar are, how to mix them, and how to use them in your next project.
What Is a Mortar Mix Ratio?
As you likely already know, all mortar is made up of three key ingredients: dry cement powder (specifically, Portland cement), lime, and sand.
While these ingredients are fairly straight forward, they can be combined in differing volumes to create mortars with differing properties. These different combinations rely on “mortar mix ratios” to ensure that they can be reliably recreated on demand without wasting raw materials or time.
As a result, a mortar mix ratio can be seen as a recipe for making certain variations of mortar.
Like a recipe, a mortar mix ratio will be expressed in terms of “parts,” as in “ 1 part cement, 1 part lime, and 6 parts sand.” In theory, these basic ingredients could then be combined using proper techniques to create mortar with a desirable consistency and productive properties after setting.
4 Common Types of Mortar: Uses and Mix Ratios
There are a wide variety of mortar mix ratios, especially when it comes to special-use applications of mortar. However, there are four main types that see the most use in professional and DIY circles: N, O, S, and M.
Each of these main types differs when it comes to durability and tensile strength, so it is important to know about each before choosing one for your project.
You may also see mention of “type K” mortar while researching the right mortar mix ratio for your upcoming project. While this type still sees use, it is limited to restoring historic structures due to its extremely low compressive strength. Should you need to make type K mortar, it can be made by combing 1 part cement, 3 parts lime, and between 10 to 12 parts sand.
Type N is the most common mortar mix ratio used on professional and amateur jobsites today. That’s because its basic recipe efficiently uses mortar’s essential ingredients while still providing a solid, reliable bond in many environments.
Because of this mixture’s strength against heat and other weather, it often sees use above grade in both exterior and interior projects. In particular, type N mortar sees a lot of use in soft stone masonry projects due to the aforementioned properties.
This mortar’s high compression strength of around 750 psi also allows it to be load-bearing if necessary.
As with any commonly used construction materials, some slight variations of type N mortar exists. However, the most common mortar mix ratio for type N is 1 part cement, 1 part lime, and 5 to 6 parts sand.
Type O is the next most common mortar type that sees use almost exclusively indoors.
This is because type O mortar, after drying, is noticeably weaker than the basic type N. In fact, it is not recommended for load-bearing use due to its meager 350 psi compression strength. Instead, it is best suited for indoor projects that are above grade.
Specifically, repointing and similar repair work can best take advantage of this type of mortar.
To make your own type O mortar, you’ll need to closely follow its established mortar mix ratio. That recipe is as follows: 1 part cement, 2 parts lime, and 8 to 9 parts sand.
Next up is type S mortar, which sees a lot of professional use in civic projects such as sewers and manhole shafts. That’s because type S, after setting, has a high tensile bond strength and high compressive strength of over 1,800 psi that allow it to withstand the pressure of below-grade applications.
Type S mortar also resists soil pressure with ease, making it a worthwhile option for use on patios and in masonry foundations.
Making your own type S mortar is fairly straight forward. Simply combine the following ingredients: 2 parts cement, 1 part lime, and 8 to 9 parts sand. This mortar mix ratio is very similar to type O mortar, so be sure to carefully measure your ingredients when making either type.
The last of the four most common mortar types is type M. This type is considered the strongest on its own, with a compressive strength of approximately 2,500 psi for most mixes.
This allows it to be used in a variety of below-grade applications, including driveways, retaining walls, and in-ground foundations. However, type M is also known for its poor adhesion and sealing properties. As such, it should never be used in an application that exposes it to the elements.
Should you need to make your own type M mortar, you can do so with the following mix ratio: 4 parts cement, 1 part lime, and 12 to 15 parts sand.
Which Mortar Type Should I Use for Block Walls, Bricks, Tiles, and Stone?
If you’re planning to build a wall using cinder blocks or bricks, you’ll need to evaluate how much pressure that wall will be bearing after completion.
If that wall will bear a modest amount of pressure, standard type N mortar should suffice while still efficiently utilizing your raw ingredients. However, if that wall will end up bearing an extra-large load, you may opt for type S mortar.
Meanwhile, if you’re interested in sealing tiles or stones together for a masonry project, then you’ll need to choose a mortar with reliable bonding properties. Your choice on this front should depend on what materials you are actually using, though.
To that end, a soft stone project (such as for a walkway) could easily use type N mortar. However, a heavy-duty paving project (such as for a patio) may warrant type S or even type M mortar.
All in all, you have some options before you if you’ve decided that you’ll be using mortar for your upcoming project. While it may take some testing and some further research, you should absolutely take the time necessary to figure out which mortar mix ratio will best suit your project’s needs.
Failure to do so may cause your mortar to degrade prematurely, perform sub-optimally, or simply fall apart under pressure beyond its capacity. None of these are desirable results, obviously.
As such, it is essential for you to determine if type N, O, S, or M will suit your project before buying raw mortar ingredients. Don’t hesitate to reach out to a trained mason, either. They can provide you with productive insights into how each type will perform in your specific environment as well as any tools you might need for the job.