When it comes to effective masonry repairs and construction it is important to use the correct type of mortar. There is an alphabet soup of mortar types including M, S, N, O and K. Do you know the difference between them? Do you know what type of mortar is needed for each structure form and materials? Did you just shrug your shoulders and shake your head no?
What you just learned is the importance of hiring a company of professionals to complete your masonry repairs. Whether the skilled masons from Oosting Custom Masonry & Chimney Service Co are working on your chimney, fireplace, foundation, sidewalk, steps, or stonework you know that we bring the expertise you need to have beautiful long AND lasting craftsmanship.
There are so many horror stories about uninformed homeowners who hire someone claiming to be a professional mason yet they use the wrong type mortar for the project. At first the structures look ok, but as weather takes its toll the structures became unstable; all because the wrong mortar was used. The homeowners are out thousands of dollars, and damage was caused because the homeowners didn’t do their due diligence in hiring contractors. We don’t want that to happen to you.
Here is a basic lesson in Mortar 101
Mortar acts as the glue that holds masonry together as well as providing a cushion to hold the masonry units apart. It fills in the cracks and gaps between the brick or rock and maintains the integrity and stability of the structure, helping to keep water out.
Mortar is a mixture of a binder such as lime or Portland cement, an aggregate (sand, gravel, crushed stone), and water. The use of mortar dates back to prehistoric times. In fact it is now believed that the use of mortar pre-dates agriculture! The Egyptian Pyramids used mortar of clay and mud or clay and sand when constructing and repairing the pyramids.
The ASTM (American Society for Testing and Materials) currently designates 5 different types of mortar for use in new construction. The ASTM explains, “Mortar cement shall conform to the prescribed requirements such as fineness, autoclave expansion, time of setting, compressive strength, flexural bond strength, air content of mortar, and water retention.”
So what is with the letter designations? According to Christine Beall writing in Masonry Construction Magazine, “Prior to 1954 mortar types were designated A-1, A-2, B, C and D. It was found that A-1 carried the connotation of being the best.” To dispel the myth a new naming scheme was implemented. The words MaSoN wOrK were taken and every other letter was removed, leaving us with M, S, N, O and K.
Type M Mortar is the hardest and is recommended for use below or at grade such as in foundations and retaining walls. Type S Mortar is recommended for similar situations and while not as hard as Type M, S is also used for foundations, retaining walls, brick patios, exterior walls, and similar projects when compressive strength is a primary consideration. Type N is the most common mortar and has more flexibility than the harder mortar and is used for soft stone and brick such as above ground walls and chimneys. K and O mortar are the most flexible and used when consideration must be given not to cause damage to the brick or stone to which it is adhering.
The complexity, however, doesn’t end there. The ASTM has two ways of designating masonry mortar, one by minimum compressive strength and one by mix ratio. The bagged mortars generally used in new construction are extremely hard and can be inappropriate for repair work. On top of that, if your building is more than 100 years old, all modern mortars are more than likely inappropriate for repairs. In these older buildings a lime mortar or natural cement mortar may be the best answer. As you can see, a deep understanding of the materials is required for correct installation and for proper, lasting repairs.
Mortar can make, or quite literally, break your structure. While we don’t expect you to be in an expert in mortar, the take away is that you are aware that different mortars perform different functions. One type of mortar does not fit all situations, no matter what someone tries to tell you. Using mortar that is too hard will cause damage to the stone or bricks it is supporting and prevent proper moisture transmission from the interior of the building, causing damage.
We don’t want you to be as vulnerable as a structure that was built or repaired with the wrong type of mortar.The expert masons from Oosting Custom Masonry and Chimney Service Company can answer all your questions, explain why they are choosing the specific materials for your project, and provide the lasting and aesthetically pleasing results you need. Call us today for excellent craftsmanship for your next project.