Mortar is an excellent for holding masonry in place. If you are planning work around your home and need to purchase mortar, you will find that it actually comes in a variety of types. Keep in mind when ordering mortar that the types are based on compressive strength. The mortar serves to create a bond that is both flexible and strong. The mortar works with both these elements to keep the masonry secure while also being flexible enough to allow for any expansion or contraction of the masonry when temperatures change.
Mortar is made from sand, cement, hydrated lime, and plain water. Depending on how the mortar is cured, some will have less water retention that can actually cause shrinkage cracks. For the lime ingredient, although it produces a lower compressive strength, the overall flexibility and strength is greater. The sand is used to add volume and help minimize shrinkage that happens as the cement begins to dry. The water is what allows the entire mixture to be workable and manageable. The water also is what activates the hydration, which is the chemical reaction needed for the cement to harden.
The various types of mortar include the following:
Type M � This is the highest compression strength and is made using 3 parts of cement, 1 part of lime, and 12 parts of sand. The strength of this type of mortar is at minimum, 2,500 psi. Generally, Type M mortar is recommended for any heavy load-bearing wall because it is durable, especially for any masonry work below grade or that would come in direct contact with earth such as retaining walls, sidewalks, foundations, and driveways.
Type S � This mortar is known for its compression and tensile strength. With a high compressive strength of around 1,800 psi and its high tensile bond, it is generally used for masonry at or below grade. To make this type of mortar, 2 parts of cement, 1 part of hydrated lime, and 9 parts of sand are used. The result is a maximum, flexural strength that is ideal for earthquakes, high winds, or pressure from the soil.
Type N � For this type of mortar, it would be used for exterior purposes on above-grade walls. The compressive strength of this type is 750 psi and made form 1 part cement, 1 part lime, and 6 parts sand. This type of mortar is used for most exterior, above-grade walls that will be exposed to all types of weather. One of the most common aspects of a home that uses Type N mortar is the chimney.
Type O � You would use this type of mortar for non-load-bearing or interior use. The compressive strength is only around 350 psi and made from 1 part cement, 2 parts lime, and 9 parts sand.
As you get ready to plan your project, you can use the guidelines to choose the type or mortar that will work for your project.