Brick Masonry: Mortar

Question 1

Why use masonry? (4)

Answer 1

• almost endless variety of colors, textures, and patterns
• masonry can take a variety of shapes, from walls to arches and vaults
• masonry is durable
• inherent fire-resistant characteristics

Question 2

What is the purpose of mortar? (4)

Answer 2

• cushions masonry units, ensuring uniform bearing
• seals joints between the units, minimizing the flow of air and water
• adheres units, providing resistance to lateral forces
• in combination with brick, mortar contributes to the appearance of the wall

Question 3

What are the ingredients of portland cement-lime mortar? (4)

Answer 3

• portland cement
• aggregate
• hydrated lime
• water

Question 4

What are some aggregate options for portland cement-lime mortar? (3)

Answer 4

• natural sand
• manufactured sand made from crushed stone, gravel, or furnace slag
• a well-graded mix with particles ranging in size from 0.003-0.187 inches in diameter

Question 5

How is hydrated lime made, and why is it used in portland cement-lime mortar?

Answer 5

• made by burning limestone or seashells

- added to improve smoothness and workability of mortar

Question 6

What sort of water is used in portland cement-lime mortar? (2)

Answer 6

• clean, neutral pH, free of contaminants or organic material
• potable water is generally considered suitable for making mortar

Question 7

Describe the mortar mixing process. (7)

Answer 7

• sand provides the basic structural body of the hardened mortar
• portland cement is the “glue” that binds the sand particles together
• lime improves the workability of mortar in its plastic state
• a minimum amount of water is necessary for the chemical hydration of the cement
• additional water is added to produce a good working consistency to the wet mortar
• stiff mortar may be “retempered” if less than 90 minutes old
• stiff mortar more than 2.5 hours old must be discarded

Question 8

What sort of admixtures are added to mortar, and what do they do? (3)

Answer 8

• pigments: colored aggregate
• accelerators and retarders: adjust setting time in cold or hot weather
• bond enhancers: improve flexural strength, freeze-thaw resistance

Question 9

What are the five mortar types, according to ASTM C270?

Answer 9

• Type N: general purpose mortar with good bonding capabilities and workability
• Type S: higher flexural strength than type N
• Type O: low strength mortar recommended for interior non-load bearing walls
• Type M: high strength mortar with less workability
• Type K: very low strength mortar used in historic preservation work

Question 10

How are mortar types selected? (3)

Answer 10

• in general, the lowest strength mortar suitable for a particular job is the optimal choice
• Type S and Type N mortars are the most commonly specified
• mortar type designations, in decreasing order of strength, come from every other letter in the words “MaSoN wOrK”