Masonry Materials, Mortars, and Grouts

Introduction

This chapter covers all materials used in masonry, their properties, their classifications, and their applications according to Canadian standards. The selection and preparation of mortars and grouts are essential skills for the bricklayer. An error in choosing the mortar type or in calculating proportions can lead to cracks, water infiltration, and structural failures. This chapter prepares you to master these aspects for the Red Seal exam.

Masonry Units: Classification and Properties

Fired Clay Bricks

Fired clay bricks are classified according to their manufacturing process and degree of resistance. The degree of firing determines porosity and resistance to water absorption.

Brick Grade	Max Water Absorption (%)	Compressive Strength (MPa)	Typical Use
Grade SW (Severe Weathering)	17%	≥ 20.7 MPa	Severe exposure, contact with soil
Grade MW (Moderate Weathering)	22%	≥ 17.2 MPa	Moderate exposure
Grade NW (No Weathering)	25%	≥ 10.3 MPa	Interior only

Classification by Type:

Type I: General-purpose fired clay brick, dimensional tolerance of ± 3 mm.

Type II: Precision fired clay brick, dimensional tolerance of ± 1.6 mm.

Type III: Facing fired clay brick, selected for its appearance.

Concrete Blocks (Concrete Masonry Units)

Concrete blocks are classified according to their density and strength. Standard CSA A165 (Standards on Concrete Masonry Units) defines the requirements.

Block Type	Density (kg/m³)	Minimum Strength (MPa)	Application
Lightweight block	< 1,680 kg/m³	7.5 MPa	Non-load-bearing walls, insulation
Medium-weight block	1,680 – 2,000 kg/m³	10 MPa	Load-bearing walls
Heavyweight block	> 2,000 kg/m³	15 MPa	Load-bearing walls, foundations

Standard nominal dimensions: 200 × 200 × 400 mm (width × height × length). The actual dimension is 190 × 190 × 390 mm, with the 10 mm difference being occupied by the mortar.

Natural Stone

Natural stone is classified into three categories according to its geological origin:

Igneous rock (granite, basalt): very strong, low absorption, used for foundations and veneers.

Sedimentary rock (limestone, sandstone): softer, more porous, used for interior veneers.

Metamorphic rock (marble, slate): strong and aesthetic, used for finishes.

Key Properties to Know:

The density of the stone influences its freeze-thaw resistance.

Water absorption must be less than 7.5% for severe exterior exposure.

Frost resistance is determined by the number of freeze-thaw cycles the stone can withstand without deteriorating (minimum 100 cycles according to CSA A82).

Refractory Clay Masonry Units

Used for chimneys, furnaces, and high-temperature areas. They must withstand temperatures from 1,000 °C to 1,650 °C. Refractory mortar is formulated with refractory clay and chamotte (ground fired clay).

Mortars: Composition and Classification

Definition and Functions of Mortar

Mortar is a mixture of binder (cement, lime, or a combination), sand, water, and sometimes admixtures. Its main functions:

31.Bond masonry units together.

32.Distribute loads uniformly.

33.Compensate for dimensional variations in the units.

34.Provide air and water tightness.

35.Ensure adhesion between units.

Mortar Types According to CSA A179

Standard CSA A179 (Mortar and Grout for Masonry Units) defines four mortar types, classified by decreasing strength:

Type	Proportion Portland Cement : Lime : Sand	Compressive Strength at 28 Days (MPa)	Recommended Use
Type S	1 : 0.5 : 4.5	≥ 12.4 MPa	Reinforced masonry, seismic zones, load-bearing walls
Type N	1 : 1 : 6	≥ 7.6 MPa	Exterior walls above grade
Type O	1 : 2 : 9	≥ 3.4 MPa	Interior non-load-bearing walls
Type M	1 : 0.25 : 3.5	≥ 17.2 MPa	Structures in contact with soil, heavy loads

Mnemonic rule: "Strong, Normal, Ordinary, Massive" — from strongest to weakest for common use, but M is the strongest in compression.

The Role of Lime in Mortar

Lime (calcium hydroxide) improves:

The plasticity and workability of the mortar.

Water retention (prevents the mortar from drying too quickly).

Self-healing capacity (microcracks close over time).

Flexibility (allows slight movement without cracking).

Hydrated lime is classified according to standard CSA A82.27 into two types:

Type N (normal hydrated lime): general use.

Type S (special hydrated lime): superior plasticity, recommended for mortars.

Masonry Sand

Sand must be clean, well-graded, and free of organic matter. The particle size distribution is controlled according to standard CSA A179.

Sand Gradation Requirements:

Sieve (mm)	% Passing (minimum – maximum)
4.75 mm	95 – 100%
2.36 mm	80 – 100%
1.18 mm	50 – 90%
0.600 mm	25 – 65%
0.300 mm	10 – 35%
0.150 mm	0 – 10%

Organic Matter Content: sand must not contain more than 0.5% organic matter. A simple test: fill a jar with sand and water, shake, and let sit for 24 hours. If the water turns dark brown, the sand is contaminated.

Mixing Water

Water must be potable, clean, and free of oils, acids, alkalis, or organic matter. Non-potable water may be used if it meets the requirements of standard CSA A3001 (comparative strength test).

Admixtures

Admixtures are products added in small quantities (less than 5% of the cement weight) to modify the properties of mortar:

Admixture	Desired Effect
Air-entraining agent	Improves freeze-thaw resistance
Accelerator	Increases setting speed in cold weather
Retarder	Slows setting in hot weather
Plasticizer	Improves workability without adding water
Water repellent	Reduces water absorption of hardened mortar

Caution: liquid "all-in-one" admixtures that replace lime are not recommended. They do not replicate the water retention and flexibility properties of lime.

Masonry Grouts

Definition and Functions

Grout is a fluid mixture of cement, lime, sand, and water, poured into the cavities of masonry units to:

Fill voids in hollow walls.

Encase reinforcing bars.

Ensure monolithic bonding between elements.

Transmit vertical loads.

Grout Types According to CSA A179

Type	Proportion Cement : Lime : Sand	Use
Fine grout	1 : 0.1 : 2.25 to 3	Cavities 25 to 75 mm wide
Coarse grout	1 : 0.1 : 2.25 to 3 (coarser sand)	Cavities 75 mm and wider

Consistency Requirements:

Fluid grout: slump of 200 to 250 mm on the Abrams cone (used for narrow cavities).

Plastic grout: slump of 150 to 200 mm (used for large cavities).

Grout Lift

Grout lift is a technique where grout is poured in a single operation to a height not exceeding 3 meters. Beyond this height, grout must be poured in stages of 1.2 to 1.5 meters maximum to prevent segregation.

Pouring Rules:

Maximum height of a single pour: 3 m.

Grout must be consolidated by vibration or rodding (puddling) to eliminate voids.

Grout temperature at the time of pouring: between 10 °C and 35 °C.

Proportion and Volume Calculations

Calculating Mortar Volume

The volume of mortar required for a wall is approximately equal to 25 to 30% of the total wall volume (including units).

Practical Formula:

Mortar volume = Total wall volume × 0.28

Example: Wall 10 m long, 3 m high, 200 mm thick.

Total volume = 10 × 3 × 0.2 = 6 m³

Mortar volume = 6 × 0.28 = 1.68 m³

Calculating Materials for Type N Mortar

For 1 m³ of Type N mortar (proportion 1 : 1 : 6):

Material	Volume (m³)	Approximate Mass (kg)
Portland cement	0.125 m³	150 kg (≈ 3 bags of 50 kg)
Hydrated lime	0.125 m³	75 kg (≈ 1.5 bags of 50 kg)
Sand	0.750 m³	1,200 kg
Water	0.250 m³	250 L

Rule of thumb: one 50 kg bag of cement produces approximately 0.04 m³ of finished mortar (with Type N proportions).

Calculating Grout Volume

The grout volume for a hollow wall is calculated based on the cavity volume:

Grout volume = Cavity volume × 0.95 (fill factor)

Example: Wall 10 m × 3 m with a 100 mm cavity.

Cavity volume = 10 × 3 × 0.1 = 3 m³

Grout volume = 3 × 0.95 = 2.85 m³

Preparation and Placement

Mixing Mortar

Manual Method (on a board):

99.Measure the volumes of sand, cement, and lime using calibrated containers (not shovels).

100.Mix dry until a uniform color is achieved.

101.Form a crater in the center and add approximately 80% of the water.

102.Mix by folding the edges toward the center.

103.Add the remaining water gradually until the desired consistency is reached.

Mechanical Method (mortar mixer):

105.Add approximately 50% of the water to the mixer.

106.Add half of the sand.

107.Add the cement and lime.

108.Add the remaining sand.

109.Add the remaining water gradually.

110.Mix for 3 to 5 minutes.

Mortar Consistency:

Plastic mortar: slides easily off the trowel but holds its shape. This is the ideal consistency for most work.

Soft mortar: slumps slightly, used for highly absorbent concrete blocks.

Stiff mortar: used for finishing jointing.

Setting Time and Pot Life

Ambient Temperature	Maximum Pot Life
> 30 °C	1.5 hours
20 – 30 °C	2 hours
10 – 20 °C	2.5 hours
< 10 °C	3 hours

Golden rule: any mortar that begins to set must be discarded. Never re-temper partially set mortar.

Cold Weather and Hot Weather Work

Cold weather (temperature < 5 °C):

Heat the sand and water to a maximum temperature of 70 °C (never heat the cement).

The temperature of fresh mortar must be at least 5 °C.

Protect fresh masonry with insulating blankets.

Do not use de-icing salts in the mixing water.

Hot weather (temperature > 30 °C):

Use cold water (10 – 15 °C).

Wet highly absorbent masonry units before laying.

Reduce the batch size of mortar prepared at one time.

Protect fresh mortar from direct sunlight.

Quality Control and Testing

Tests on Fresh Mortar

Test	Method	Acceptable Value
Slump (Abrams cone)	ASTM C143	100 – 150 mm for mortar
Water retention	ASTM C1506	≥ 70%
Air content	ASTM C231	10 – 18% for mortar
Temperature	Thermometer	5 – 35 °C

Tests on Hardened Mortar

Compressive strength: test on 50 mm cubes, tested at 7 and 28 days.

Bond strength: direct tensile test on masonry prisms.

Water absorption: measurement of the porosity of hardened mortar.

Sample Collection

Mortar samples must be taken at the point of use (not from the mixer). Prepare at least three 50 mm cubes per sample. Store the cubes under standard conditions (23 °C ± 2 °C, relative humidity > 95%) for 28 days.

Applicable Canadian Standards

Standard	Title	Application
CSA A179	Mortar and Grout for Masonry Units	Classification and requirements for mortars
CSA A165	Standards on Concrete Masonry Units	Requirements for concrete blocks
CSA A82	Fired Clay Bricks	Classification and requirements for bricks
CSA A82.27	Hydrated Lime for Mortar	Requirements for lime
CSA A3001	Cementitious Materials	Requirements for Portland cement
CSA S304	Design of Masonry Structures	Design and calculation of walls
NBC (National Building Code)	Chapter 1, Division B, Section 4.3	Durability requirements for materials
NBC	Chapter 1, Division B, Section 9.20	Masonry for small buildings

Pitfalls to Avoid

141.Confusing mortar types: Type S is the strongest for common applications, not Type M. Type M is reserved for structures in contact with soil.

142.Using proportions by mass instead of volume: mortar proportions are always by volume. A 50 kg bag of cement does not correspond to a volume of 50 L.

143.Neglecting the temperature of mixing water: water that is too hot (> 70 °C) accelerates setting and reduces final strength.

144.Re-tempering partially set mortar: this is a serious error that reduces strength by 50% or more.

145.Confusing grout and mortar: grout is more fluid, contains more water, and is poured (not spread with a trowel).

146.Ignoring water retention: mortar with poor water retention dries too quickly on absorbent blocks, causing poor adhesion.

147.Using sea sand or contaminated sand: salt and organic matter cause efflorescence and reduce adhesion.

148.Forgetting the grout fill factor: grout volume is never equal to cavity volume (factor of 0.95).

149.Failing to protect masonry in cold weather: mortar must remain above 5 °C for the first 48 hours.

150.Confusing brick grades: Grade SW is for severe exposures, not Grade NW.

Summary

Masonry units are classified by material (clay, concrete, stone), by grade (SW, MW, NW), and by type (I, II, III).

Mortars are classified into four types (M, S, N, O) according to CSA A179, with precise volumetric proportions.

Lime improves the plasticity, water retention, and flexibility of mortar.

Sand must be clean, well-graded, and conform to the gradation requirements of CSA A179.

Grouts are fluid mixtures poured into cavities, classified as fine or coarse depending on cavity width.

Mortar volume represents approximately 28% of the total wall volume.

Pot life of mortar varies from 1.5 to 3 hours depending on temperature.

Key standards: CSA A179 (mortar and grout), CSA A165 (blocks), CSA A82 (bricks), CSA S304 (design), NBC Sections 4.3 and 9.20.

Quality control includes tests on fresh mortar (slump, water retention, air content) and hardened mortar (compression, bond).

Extreme weather conditions (cold and hot) require special precautions for preparation and placement.

Priority Review Points for the Exam:

163.Exact proportions of the four mortar types (M, S, N, O).

164.Minimum compressive strengths at 28 days.

165.Sand gradation requirements.

166.Maximum grout pour height (3 m).

167.Temperature limits for mixing and placement.

168.Pot life according to temperature.

169.Volume factor for mortar (28%) and grout (95%).

170.Classification of bricks (grades and types) and blocks (density and strength).

Masonry Materials, Mortars, and Grouts