The Mason's Journal

When it comes to masonry projects, whether you're restoring an aging brick façade or constructing a retaining wall, one critical element often gets overlooked—the mortar. Choosing the right type of mortar isn’t just important; it’s essential. Using the wrong mortar can lead to structural weaknesses, early deterioration, and costly repairs. On the other hand, selecting the right mortar ensures durability, a seamless appearance, and protection against the elements. If you've thought to yourself, “How do I choose the right masonry mortar?” or Googled “masonry near me,” this post is for you. Below, we'll explore the different types of mortar, their specific uses, and why understanding these distinctions is key to the success of your project. What Makes Mortar Important? Mortar isn’t just there to "glue" bricks, stones, or blocks together—it’s also a vital part of a structure’s strength and resilience over time. The correct mortar acts as a buffer, accommodating thermal expansion, contraction, and movement while maintaining a watertight seal. Selecting the wrong type of mortar, however, can lead to mismatched tensile strength with the masonry material, increasing the risk of cracks, water intrusion, or even collapse. That’s why homeowners, property managers, and building owners alike should understand mortar types before starting any repair or construction project. The M-A-S-O-N-W-O-R-K Rule for Choosing Mortar A great way to simplify this process is by using the “M-A-S-O-N-W-O-R-K” rule. It’s an acronym to remember the five types of mortar—M, S, N, O, and K—and their order, which ranks them from the hardest (highest PSI) to the softest (lowest PSI): M – S – N – O – K This sequence makes it easy to determine which mortar may fit your project's strength requirements and aesthetic goals. Now, let's break down each type and its applications. Type M Mortar—The Powerhouse of Masonry Strength: 2,500 PSI Type M mortar is the strongest option, designed for heavy-duty applications. It's typically used in projects that demand maximum strength, such as load-bearing walls, foundations, or retaining walls made of stone. Type M is also ideal for structures exposed to severe weather, wind, or soil pressure. Applications: Retaining walls Foundations supporting heavy loads Stone structures or natural rock masonry While its high strength is a benefit, Type M is overkill for most residential projects. Using it with softer bricks or stones may actually cause damage due to lack of flexibility. Type S Mortar—Strength Meets Versatility Strength: 1,800 PSI Type S mortar strikes a balance between strength and workability, making it a versatile option. It has excellent tensile bond strength, which helps it withstand movement and seismic activity. For masonry below grade, such as basement walls or outdoor patios, Type S is an excellent choice due to its durability. Applications: Exterior walls requiring flexibility and weather resistance Masonry exposed to soil or moisture (below grade) Patios, walkways, and retaining walls Type S is widely used in residential masonry—it’s a fantastic all-rounder for repairs and new builds. Type N Mortar—The All-Purpose Solution Strength: 750 PSI Type N mortar is a go-to for many residential applications involving above-grade masonry. 90% of the mortar we use on our projects is Type N mortar. Its medium strength makes it perfect for structural and aesthetic purposes, combining the right amount of durability and flexibility to accommodate shifting and settling. Applications: Exterior brick or stone facades Chimneys with moderate exposure to weather Decorative masonry like garden walls Type N offers simple workability and is less rigid than Type M or S, making it a preferred choice for homeowners prioritizing appearance and usability. Type O Mortar—A Niche Choice for Historic Preservation Strength: 350 PSI When it comes to mortar, Type O is far from the strongest option available. In fact, it’s one of the weakest, with a low compressive strength of just 350 PSI. This makes it unsuitable for load-bearing applications and most modern masonry projects. However, it does have a specialized role—preserving historic structures. Older bricks, particularly those found in vintage homes and historic Twin Cities landmarks, were not designed to withstand the rigidity of modern mortars. Type O’s softness and high workability allow it to bond without damaging delicate masonry, making it a necessary compromise rather than a go-to solution. Applications: Repairing fragile, historic brickwork Non-load-bearing interior walls Patching deteriorating masonry where a softer mortar is essential If you're restoring an older property, Type O mortar might be required to prevent damage to aged bricks—but it’s not a universal fix. In most cases, stronger, more durable mortars are the better choice for lasting stability. Type K Mortar—The Rarely-Used Keeper Strength: 75 PSI The softest of all mortar types, Type K is rarely used in modern construction. However, it’s highly valued for repairing historic structures with exceptionally soft bricks or stones. With minimal PSI, it ensures that aged materials aren’t damaged by excessive mortar strength. Applications: Extremely delicate, historic masonry restoration Interior, non-load-bearing walls in vintage properties If your project involves restoring any pre-1900s Twin Cities architecture, consult an expert for Type K usage. Adding Personality with Custom Mortar Dyes Once you've determined the type of mortar for your project, you can further customize its appearance with custom mortar dyes. These dyes allow you to match the cement color to surrounding masonry, making repairs virtually invisible. Capital Masonry Restoration offers expert dye matching for projects throughout the Twin Cities, helping your structure maintain its polished and cohesive look. Why Capital Masonry Restoration is Twin Cities’ Top Choice With a deep understanding of the unique climate and architecture in the Twin Cities, Capital Masonry Restoration is your trusted partner for quality masonry repair and restoration. Whether you're repairing a crumbling chimney, constructing a durable retaining wall, or completing historic preservation work, our experienced team is here to guide and execute your project with precision. Curious which mortar is best for your masonry? Contact us today to discuss your project or schedule a free consultation.