Bricks and Mortar

Question 1

If a brick is classified as ‘OL’, it is?

Answer 1

Not frost resistant and low salt content

Question 2

If an engineering brick is classified as ‘B’, it has a strength between (N/mm2)?

Answer 2

50 - 70 N/mm2

Question 3

Typically what is the compressive strength range for bricks (in N/mm2)?

Answer 3

15 - 140 N/mm2

Question 4

The cement content in lime mortar is typically (%)?

Answer 4

0%

Question 5

Bricks are usually fired for (hours)?

Answer 5

Between 10 and 40 hours, depending upon kiln type and other variables

Question 6

What is the current UK (also global standard) brick size?

Answer 6

215mm x 102.5mm x 65mm

Question 7

Specification for Clay Bricks?

Answer 7

BS EN771 - replaced BS 3921

Question 8

How do water absorption ranges in bricks?

Answer 8

Ranges from very low (dense) to 0 to 25% water absorption for very porous bricks

Question 9

Name different types of bricks

Answer 9

Solid - no holes, cavities or depressions
Frogged - depressions usually not greater than 20% of the total volume
Perforated - holes not exceeding 25% of gross volume for use in structural applications
Facing Bricks - appearance, frost resistance & strength – the majority of bricks nowadays
Engineering Bricks - dense & low water absorption, higher strength, frost resistance
Structural & Domestic Brickwork - has low stresses generally

Question 10

What does Frost resistant (F) mean?

Answer 10

Resistant in all situations - repeated freezing and thawing

Question 11

What does Moderately frost resistant (M) mean?

Answer 11

Durable except when saturated & repeated freezing /thawing

Question 12

What does Not frost resistant (O) mean?

Answer 12

Liable to damage by the frost – hence suitable for internal use only

Question 13

What does fired brick consist of?

Answer 13

Sodium, potassium, magnesium sulphates exist in the fired brick – with time these may slowly attack the hardened mortar

Question 14

What are the two categories for salt content in bricks?

Answer 14

‘Low’ (L) & ‘Normal’ (N)
FL ~ Frost resistant (F) & low salt (L)
FN ~ Frost resistant (F) & normal salt (N)
ML ~ Moderate (M) & low salt (L)
OL ~ Not frost resistant (O) & low salt (L)

Question 15

What is efflorescence?

Answer 15

It is white staining on brickwork due to salts crystallizing on the surface in springtime

Question 16

How does moisture movement affect bricks?

Answer 16

Clay bricks slowly expand with time whereas mortar shrinks – the net effect is a slow expansion of walls – require movement joints at regular intervals to accommodate expansion and prevent stress build-up in wall

Question 17

How does a chemical attack affect bricks?

Answer 17

Bricks generally have very good resistance to chemicals - mortar is the weak link

Question 18

Are bricks fire resistant?

Answer 18

Bricks have very good fire resistance as they are fired in the kiln at 900°C+

Question 19

What are clays composed of?

Answer 19

Silica and alumina with varying amounts of metallic oxides. Metallic oxides promote the fusion of the particles at lower temperatures.

Question 20

How does Metallix Oxices affect clays?

Answer 20

Metallic oxides promote the fusion of the particles at lower temperatures. Metallic oxides (particularly those of iron, magnesium and calcium) also influence the colour of the fired brick.

Question 21

What happens to bricks in high temperatures?

Answer 21

The firing of clay bricks Clay, unlike metal, softens slowly and melts or vitrifies gradually when subjected to rising temperatures.

Question 22

What does Vitrification do to clay?

Answer 22

Vitrification allows clay to become a hard, solid mass with relatively low absorption.

Question 23

What does the firing process involve?

Answer 23

The firing process involves decomposition of clay minerals to component oxides & re-crystallization into new compounds - durable, glassy matrix formed

Question 24

What are the requirements of modern mortar?

Answer 24

Adhere to bricks/stone/blocks, high plasticity & workability, adequate stiffening rate, good durability, frost, sulphate attack and rain penetration resistant, appearance and colour - Architects specification

Question 25

What designation mortar is mostly used?

Answer 25

In most buildings / dwellings Designation (iii) or (iv) mortar used

Question 26

What type of Mortar is available?

Answer 26

Mix on-site, factory prepared wet lime/sand mixes, or ready mixed cement+lime+sand+retarder+colouring agents are common nowadays (usually last 36-48 hours before setting)

Question 27

What are commonly used additives to mortar?

Answer 27

Plasticisers are commonly used to improve workability (hydrated lime), adhesion, spread – not FAIRY LIQUID as it can cause efflorescence…. a very common practice!

Question 28

What are Lime Mortars?

Answer 28

Much lower embodied carbon than cement-based mortars. Comprised usually of 1 part lime & 3 parts sand.

Question 29

What is Lime Mortar effective at?

Answer 29

Very flexible and able to withstand greater movements without cracking. Allows building to ‘breath’, thus fewer issues with dampness - Majority of old/historic buildings made using lime mortar

Question 30

What is Traditional Mortar made of?

Answer 30

Lime and sand (no cement) – typically ratio of 1:3 or 1:2 by volume – e.g. bucketfuls

Question 31

What is Traditional Morta effective at?

Answer 31

Plastic mortar, high workability, low strength, flexible and hardens slowly.

Question 32

Why is cement preferred instead of lime?

Answer 32

Quicker strengths but less accommodating – cracks easily

Question 33

What are the two different Lime Mortars?

Answer 33

Hydraulic Lime Mortar - Non-Hydraulic Lime Mortar.

Question 34

What is Hydraulic Lime Mortar?

Answer 34

Hydraulic means to harden underwater and is considered between cement and non-hydraulic mortars.

Question 35

What is Hydraulic Lime Mortar made of?

Answer 35

The mix contains dicalcium silicate but unlike cement mortars no tricalcium silicate. The dicalcium silicate (with water) provides the setting properties of hydraulic lime. 3 strength grades specified in EN 549: NHL2, NHL3.5 & NHL5 (N/mm2) - the numbers indicate approximate strength

Question 36

What is Non-Hydraulic Lime Mortar?

Answer 36

Hardens by reaction with atmospheric carbon dioxide - called carbonation. The reaction with carbon dioxide produces calcium carbonate. Usually takes several days to gain initial hardness and therefore can delay construction progress. Commonly known as lime putty. In projects, unspecified amount of PFA or slag added to reduce setting time