Masonry cements are a specialized type of hydraulic binder that forms the essential ingredient in mortars for brick, block, and stone masonry. Engineered to provide enhanced workability, water retention, and durability compared to regular cements, masonry cements are a key component of strong, long-lasting masonry construction. In this ultimate guide, we’ll walk you through everything you need to know about these powerful and versatile cements.

What are Masonry Cements?

Masonry cements are carefully formulated mixtures of Portland clinker, plasticizers like ground limestone or hydrated lime, and air-entraining agents. This special composition gives masonry cements a unique set of properties perfectly tailored for mortar and stucco applications in unit masonry construction.

The primary functions of masonry cements include:

• Providing high bond strength between masonry units
• Enhancing plasticity and cohesion of the fresh mortar
• Improving water retention to enable proper curing
• Entraining stable microscopic air voids for freeze-thaw durability
• Enabling smooth, attractive and uniform finishes

When mixed with the proper proportions of masonry sand and water, masonry cements form the binder that literally holds masonry walls together.

Composition and Types

Ingredients

Masonry cements are manufactured by inter-grinding the following raw materials into a fine, homogenous powder:

• Portland clinker: The main active ingredient that reacts with water to form hardened paste. Typically 50-70% by mass.
• Limestone or hydrated lime: Serves as a plasticizer that improves cohesion, water retention, and spread ability. Added at 5-50%.
• Gypsum: A small amount (3-5%) is used to control the setting time.
• Air entrainers: Surfactants that stabilize microscopic air bubbles during mixing. Used at <0.1%.
• Other additives: Water repellants, pigments, etc., may be included for enhanced performance.

Grades

ASTM C91 specifies three main grades of masonry cements based on their 28-day compressive strength:

Type	Min. Strength (MPa)	Uses
N	5.2	General-purpose, above-grade, non-load-bearing
S	12.4	High flexural bond, below-grade
M	17.2	Highest strength, load-bearing, sulfate exposure

Type N is the most common general-purpose grade, while Types S and M provide additional strength and durability for more challenging applications.

Key Properties

The special formulation of masonry cements gives mortars made with them several advantageous properties:

Workability

Thanks to the ball-bearing effect of entrained air and the plasticizing action of limestone powder, masonry mortars have a soft, buttery, highly workable, and cohesive consistency. Masons can easily spread the mortar and fill the head and bed joints for maximum bond. The improved workability also provides a longer board life.

Water Retention

The increased fineness and specific surface area of masonry cements enable them to effectively retain mixing water. This is critical to prevent premature stiffening and desiccation of the mortar, especially in hot, dry or windy conditions. Proper water retention allows the cementitious reactions to proceed fully so the mortar can develop its full strength potential.

Compressive Strength

Although not as strong as structural concrete, hardened masonry mortars still develop impressive compressive strength – over 17 MPa (2500 psi) in the case of Type M. This provides ample load-bearing capacity for most masonry applications, including multi-wythe load-bearing walls. Strength gain continues over months.

Bond Strength

The high degree of plastic cohesion in masonry mortars leads to strong and complete bonding with bricks, blocks, and stones. Flexural bond strengths over 0.2 MPa (30 psi) are typical, even with smooth, dense units. The exceptional bond also contributes to water penetration and structural robustness.

Durability

The 8-20% air content entrained into masonry mortars acts like a pressure relief system during freeze-thaw cycles. As residual water in the mortar expands upon freeing, it can enter the flexible air void system instead of building up destructive internal stresses. This greatly improves freeze-thaw durability compared to non-air-entrained mortars.

Masonry cements also typically have lower shrinkage and better sulfate resistance than straight Portland-lime mortars, thanks to their engineered particle size distribution and chemistry.

Esthetics

The fine limestone particles act as a pigment to lighten the color of the mortar and provide a smooth, creamier texture. The cohesive yet buttery consistency allows masons to tool joins cleanly when thumbprint hard for a tight, uniform, and attractive appearance. Pigments can also be integrated for a wide range of color options.

Manufacturing Process

The production of masonry cements involves the following key steps:

1. Raw materials preparation: Limestone, clay, and other raw ingredients are quarried, crushed, ground, and proportioned to the proper chemistry.
2. Clinker production: The raw mix is preheated, then fired in a large rotary kiln at temperatures up to 1450°C to form partially fused clinker nodules.
3. Finish grinding: The cooled clinker is interground with 5-50% limestone or hydrated lime, as well as gypsum and other additives, in large ball mills into a fine powder with a Blaine fineness around 600 m2/kg.
4. Quality control: Samples are regularly tested for fineness, density, chemistry, air content, water retention, setting time, strength gain, and other parameters as per ASTM C91.
5. Packaging and distribution: The finished product is stored in sioss, then packaged in bags or bulk containers for transport to ready mix plants, construction sites, or masonry supply distributors.

Applications

Thanks to their excellent workability, water retention, bond, strength, and durability, masonry cements are used extensively for mortars in unit masonry construction such as:

• Residential and commercial brick/block walls
• Structural and veneer masonry
• Stone masonry
• Stuccos and plasters
• Pavers and retaining walls
• Foundations and manholes
• Sewers and tunnels
• masonry in contact with soil
• Marine masonry exposed to sulfates

When combined with masonry sand meeting ASTM C144 and sufficient water, masonry cements can be used to produce mortars that meet the proportion or property specifications of ASTM C270:

Mortar Type	masonry Cements	Portland or Blended Cements	Hydrated Lime
M	S or M	M	S
S	S or M	S	S
N	N	N	S
O	N	N	N

Best Practices

To achieve masonry construction of the highest quality and durability with masonry cements, follow these guidelines:

• Material selection: Use only masonry cements conforming to ASTM C91 and masonry sands meeting ASTM C144. Ensure compatible water.
• Mixing: Use mechanical mixers and avoid hand mixing. Add water slowly until the desired consistency is reached, but don’t overwater. Discard mortar after 2.5 hours.
• Placing: Lay units on a full bed of mortar and fill head joints by shoring. Avoid deeply furrowed bed joins. Keep cavity clear.
• Tooling: When mortar is thumbprint hard, use concave, vee, or gointed tooling to seal the join and provide a clean, uniform appearance.
• Protection: Cover walls with plastic or damp burlap to prevent rapid desiccation from sun, heat, and wind. Protect from freezing until strength is gained.
• Cleaning: Remove mortar smears from masonry before hardening using brushes, scrapers, or water. Avoid strong acids. Clean walls regularly.

The Bottom Line

Masonry cements are engineered binder materials that impart masonry mortars with an exceptional balance of workability, bond, strength, and durability that enables strong and long-lasting masonry structures of all kinds. By understanding these.

Get our professional masonry service; by just filling out the form or call.