Pro Tip

The Difference Between Mortar and Cement

Mortar is a mixture of sand and cements that is most often used to build brick or block walls. While that may sound like the same recipe used to make concrete, there are some intentional differences between the formulations for mortar and cement, which is why the materials should not be used interchangeably.

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What is the difference between mortar and cement?

If portland cement concrete is one of the most widely used building products in the world, masonry mortar is close behind. Like concrete, mortar is also designed to be durable, but achieves its goal through finesse. Its strengths are quite low compared to concrete and it is never used in thick applications. It is much creamier and more workable than concrete.

If you play tennis, think of concrete as your most powerful serve when you are trying to smash the ball into or through your opponent so that they can't return the serve. Then think of mortar as a very gently placed lob close to the net that gets your opponent leaning the wrong way with no chance of returning the ball. Both achieve the desired result of earning you a point. The point of this long-winded analogy is to let you know that using concrete and mortar interchangeably will lead to disaster.

How To Mix Mortar

Mortar can be made in one of two ways. The older method is to take portland cement, add hydrated lime and mix with fine sand. The newer method is to use masonry cement and fine sand. Masonry cement is simply a material made by most cement companies where they intergrind the portland with lime or other ingredients designed to produce high air content in a kiln. The results are the same. If you go to the store and buy a bag of mortar you will not be able to tell which method was used to make the masonry cement. There are some parts of the country where masonry cement is simply not available and you will only get portland/lime mortar. The good thing is that it doesn't matter. Some masons will absolutely swear that you must use portland/lime while others insist masonry cement is the way to go. Just chalk it up to personal preference.

There are three things that make mortar very different from concrete

1. Mortar has lower strengths than concrete
2. Mortar must have the ability to retain water
3. Mortar has a high air content compared to concrete

There are three widely produced types of mortar: Types M, S and N. Type M will achieve a compressive strength of psi at 28 days. Type S will yield while Type N yields 750. By way of reference most general concrete is in the psi range but can go as high as psi for special applications. The easy way to remember the strengths is by spelling out the word MASON WORKS.

Types O and K are not made commercially and can only be used for non-structural applications such as fixing old mortar that has fallen out.

Why isn't mortar as strong as concrete?

Why not make mortar as strong as concrete? Shouldn't all materials be as strong as possible? When you build a wall, you want the block or brick to be the strongest part of the wall. When the wall shifts, and almost all do over time, the weakest part is going to break. If the brick or block were to break, then the fix would be building a new wall. If the mortar crumbles, provided you don't let it go on for years, you simply need to repoint the wall (replace mortar in areas where the old mortar fell out). This is a simpler and more inexpensive fix. One important reason why masonry cement or a portland/lime blend works well in a mortar joint and straight portland does not is the high air content. When temperatures dip below freezing, the water content in mortar freezes. As we know, frozen water takes up more space than liquid water. This means that it will expand and crack whatever is next to it. By intentionally putting lots of tiny air bubbles in the mortar, the expanded ice has somewhere to go without causing damage. Concrete generally has enough mass that this isn't a problem.

Mortar must also be able to retain water for a certain period of time. Most masons mix up enough mortar to be able to lay a good amount of brick or block without having to stop and mix more. If the mortar they mixed doesn't retain its flowable nature for at least an hour, the mason will simply add more water to bring it back to life. While this is a really bad idea, it is done in the field all of the time. The problem with this is that the strength of the mortar is designed around certain water to cement ratio. If the ratio is skewed, then so are you when the walls fail due to weak mortar.

Which Type of Mortar Should I Use?

So which mortar should I use? Commercial jobs will usually state which you are required to use. For non-specification work, Type S is usually a safe bet and is what most of you would use on your projects. For those who have a quest to know more, the best general rule is that if the wall is non load-bearing, such as a divider wall inside of a building, then Type N is sufficient. If the wall is below grade or carrying the load of the roof or several stories of brick or block use Type S. Type M is rarely called for and only used in certain large commercial projects.

Regardless of the type of project, we recommend using our sister brand, Amerimix. While Sakrete mortars are excellent, Amerimix pre-blended mortars, stuccos and grouts have additional chemistry to extend board life, improve adhesion and simply be a more mason-friendly mix. Learn more about the Amerimix portfolio at Amerimix.com.

Mortar bonds bricks or other masonry units and strengthens walls and other structures. Type S mortar mix, in particular, is load-bearing and performs extremely well to withstand pressure from soil, wind, and seismic loads.

However, there are other types of mortar mixes'types N, O, and M'that are mixed with different ratios of cement, lime, and sand to produce specific performance characteristics, emphasizing flexibility, bonding properties, and compressive strength. The best type of mortar and its use depends on the application and the design specifications for the project.

Tip

Mortar material is made with Portland cement, hydrated lime, and sand. Thinset mortar, used with drywall and cement board is different, as it is a moisture-resistant adhesive made of Portland cement, water, and fine sand.

Type S Mortar Mix

Type S mortar mix offers high compressive strength of over 1,800 psi and high-tensile bond strength. This makes type S mortar mix suitable for many projects at or below grade.

Type S mortar mix is a load-bearing mix that can withstand pressure from the structure that it is bearing, as well as pressure from soil, wind, and seismic loads.

The most common ratio formula for Type S mortar is two parts Portland cement, one part hydrated lime, and nine parts sand. It can be mixed at different ratios for strengths reaching 2,300 and 3,000 psi.

Type S is the common choice for many below-grade applications, such as masonry foundations, manholes, retaining walls, and sewers, as well as at-grade projects like brick patios and walkways. Lime gives type S its water-resistant properties, as opposed to mortar mixes with lower ratios of lime.

Type S Consistency

When type S mortar mix is used for joining masonry units, lay about 1/2- to 2/3-inch of mortar. Test the consistency of the mortar by pressing it with your thumb; you should be able to leave a thumbprint in the mortar.

Type N Mortar Mix

Type N mortar is a general-purpose mix usually recommended for exterior and above-grade walls (including stone veneer) exposed to severe weather and high heat.

Type N mortar mix has a medium compressive strength and is composed of one part Portland cement, one part lime, and six parts sand.

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Type N mortar mix is useful for above-grade, exterior, and interior load-bearing installations. It is also the preferred mortar mix for soft stone masonry (such as limestone). Type N is the mortar most often used by homeowners and is the best choice for general application. It typically achieves 750 pounds per square inch (psi) strength within 28 days.

Tip

With any type of mortar mix, it's good practice to apply a roll-on liquid waterproofing membrane to seal the masonry work once completed.

Type O Mortar Mix

Type O mortar mix has relatively low compressive strength, at about 350 psi. As such, it is used primarily for interior, above-grade, non-load'bearing walls.

Type O mortar mix can be used as an alternative to Type N for some interior applications, but its exterior use is limited due to its low structural capacity.

Type O mortar mix is not recommended in areas subjected to high winds. However, type O mortar mix is ideal for repointing and similar repair work on existing structures, due to its consistency and ease of application. 

Tip

If you are working with glass block, you will need a special white glass block mortar. Though technically considered a type S mortar, it is formulated to exceed the strength requirements of type S mortar for this type of project.

Type M Mortar Mix

Type M mortar mix has the highest amount of Portland cement and is recommended for heavy loads and below-grade applications, including foundations, retaining walls, and driveways.

While type M mortar provides at least 2,500 psi of compressive strength, it offers relatively poor adhesion and sealing properties, making it unsuitable for many exposed applications. Type M is preferred for use with natural stone because it offers similar strength to that of stone.

Tip

If you're working on a project such as a fire pit, fireplace, or chimney, you will need to use a special high-heat mortar, also known as refractory mortar, which is formulated to handle high temperatures.

Type K Mortar Mix

Type K mortar is rarely used for new construction but may be specified for restoration or other specialty applications. It offers a very low compressive strength of only about 75 psi.

Because of its softness, type K is primarily used for restoring the masonry on historic or ancient buildings that require a special mix that is not significantly stronger than the existing masonry.

FAQ

• Which type of mortar is the strongest?

  The strongest type of mortar is type M mortar mix. This mortar contains the most cement in its ratio, making it ideal for heavy applications like foundations and retaining walls.

• Can I use Type S mortar without sand?

  Type S mortar cannot be used without sand. Type S mortar mixed without sand may shrink and fail. Pre-mixed type S mortar will always contain sand.

• How long does mortar take to harden?

  Most mortar mixes cure to 60-percent strength one full day after application. They reach full compressive strength 28 days after application.

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