CE 264 Engr.Rhodora A.Bustamante Class: Mortars and Plasters

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Questions and Answers

What is the primary purpose of mortar?

To provide insulation for walls

To increase the strength of concrete

To glue masonry units together or attach them to a receiving structure (correct)

To act as a finishing coat on walls

What is the recommended cement to sand ratio for first-class mortars?

1 part cement to 1 part sand

2 parts cement to 1 part sand

1 part cement to 3 parts sand (correct)

1 part cement to 4 parts sand

What is the purpose of adding hydrated lime to cement mortar?

To change the color of the mortar

To reduce the cost of the mortar

To increase the workability and strength of the mortar (correct)

To increase the setting time of the mortar

What is the recommended cement to sand ratio for the top surface of floors and walks?

1 part cement to 1 part sand Signup and view all the answers

What is the primary difference between mortar made with fine sand and mortar made with coarse sand?

Mortar made with fine sand requires a much larger quantity of cement to obtain a given strength Signup and view all the answers

What is the preferred method for mixing large quantities of mortar?

Mixing in a mechanical mixer Signup and view all the answers

What are the types of bricks most frequently used in architecture?

Common brick only Signup and view all the answers

What special characteristics do glazed bricks have?

Smooth outer surface with a dull finish or gloss Signup and view all the answers

Which type of brick is used for lining furnaces, fireplaces, and chimneys?

Fire (refractory) brick Signup and view all the answers

In what pattern are bricks laid for a herringbone bond?

Diagonal pattern Signup and view all the answers

Which type of bond consists of five stretcher courses and then a header course?

Common Bond Signup and view all the answers

What is the purpose of facing bricks in masonry work?

To provide specific surface characteristics for exposed surfaces Signup and view all the answers

What is the purpose of bonding plaster?

Develops more adhesive strength for interior finish on smooth concrete walls or ceilings Signup and view all the answers

When is lightweight gypsum plaster typically used?

When weight is important and for fireproofing other materials like steel Signup and view all the answers

What is the composition of a sand float finish?

1 Keene’s cement, ¼ lime putty, 1/10 fine white sand by weight Signup and view all the answers

What is the purpose of Keene’s cement?

Mixed as a hard finish for two and three-coat gypsum plaster for interior use Signup and view all the answers

What is the key function of molding plaster?

Specially designed for ornamental plaster work and castings Signup and view all the answers

When should a 1/3 gypsum plaster, 1 lime putty mixture be used?

As a hard finish in combination with fine white sand Signup and view all the answers

What are the usual mortar joint sizes between brick courses?

3/16” and ½” Signup and view all the answers

Which ingredient is NOT typically used in the production of Concrete Hollow Blocks?

Lime Signup and view all the answers

What type of aggregates can be used in the production of lightweight concrete hollow blocks?

Cinders, Expanded slag, Expanded shale or clay Signup and view all the answers

Which type of concrete hollow block has the highest fire resistance?

Expanded slag block Signup and view all the answers

For what purpose should CHB of 100mm (4”) thickness be used?

Interior partition walls where weather-tightness is not needed Signup and view all the answers

Which type of concrete hollow block is NOT mentioned in the text?

Pillars Signup and view all the answers

What does the term 'plaster' typically refer to?

Gypsum plaster Signup and view all the answers

What is the purpose of adding fiber or hair to the plaster mixture?

To increase the strength of the first coat Signup and view all the answers

In a three-coat plastering job, what is the purpose of the brown coat?

The straightening coat applied after the scratch coat Signup and view all the answers

What is the purpose of the scratch coat in a three-coat plastering job?

To act as a binding coat for the subsequent coats Signup and view all the answers

In a two-coat plastering job, how are the scratch coat and brown coat applied?

The scratch coat and brown coat are combined into one coat Signup and view all the answers

What is the recommended practice for retempered mortar?

Discard the mortar once it has begun to set and retemper a new batch Signup and view all the answers

Study Notes

Mortars and Plasters

Mortar: a proportioned mixture of siliceous materials (sand, crushed stone) and cement (lime, Portland) that hardens into a stonelike mass
Mortar is used to glue masonry units to each other or to a receiving structure like a wall or floor
Plaster: mortar applied to wall surfaces as a preparation or a hard finish coat

Cement Mortar

A proportioned mixture of cement, fine aggregate, and water
For first-class mortars, 1 part of cement should be mixed with not more than 3 parts of sand
Replacing 10-15% of cement with hydrated lime gives greater workability and increases strength
Mixing can be done by hand or mechanical mixers, with the latter preferred for large quantities

Unit Masonry

Bricks: types include common, facing, glazed, and fire (refractory) bricks
Standard brick size: 3-3/4” x 2-1/4” x 8”
Brick work: common bond, English bond, Flemish bond, and herringbone patterns

Types of Plaster and Their Uses

Gypsum plaster: bonding plaster, lightweight gypsum plaster, and fire-resistant plaster
Gypsum plaster uses: interior finish, smooth concrete walls or ceilings, and fire-proofing other materials
Keene's cement: used for hard finish, mixed with alum or borax, and burned at 932°F
Plaster of Paris: used for ornamental plaster work and castings

Concrete Hollow Block

A hollow masonry unit made of water, Portland cement, and aggregates like sand, gravel, and crushed stone
Lightweight concrete hollow blocks can be made with aggregates like cinders, expanded slag, and expanded shale or clay
Standard CHB sizes: 100mm (4”), 150mm (6”), and 200mm (8”) x 200mm (8”) x 400mm (16”)
Types of concrete hollow block include stretchers, corner blocks, headers, jamb blocks, and beam or lintel blocks

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Description

This quiz covers the topic of mortars and plasters, which are proportioned mixtures of siliceous materials and cement that harden into stonelike masses. Mortar is used to glue masonry units or surface finishing materials, while plaster is applied to wall surfaces as preparation or finishing.