STONES

LECTURE # 03

STONE MASONRY

The art of building the structures in stones with any suitable mortar is called stone masonry.

Stone is not easily and cheaply available in all parts of a country.

They are difficult to handle because of their heavy weight.

They are costly in construction as they involve high transportation and dressing charges.

CHARACTERISTICS OF GOOD QUALITY STONES

Stone is extensively used in construction industry. Not every stone can give great results because it depends upon various factors which assign different properties to stone.

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Main Characteristics of a Good Building stone are following:

Appearance & color – Uniform color, darker shades are preferred. Should be free from clay holes, bands or spots.

Structure – Not dull in appearance, crystalline homogenous, close and fine grained is good. Stratification should not be visible.

Weight – Heavier are compact, less porous and are good for hydraulic structures.

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Strength – Generally compressive strength is needed. Igneous rock stones are stronger.

Hardness– Resistance to abrasion, friction and wear. Its measured on Moh’s Hardness scale.

Toughness – Withstands impact, vibrations, moving and dead loads.

Dressing – Uniform texture and softness for fine surface finish. Important for face work of public buildings.

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Porosity and Absorption – Exposed surface absorbs rain water which forms acids causing crumbling action. Less porous stones absorb less fluid hence are more durable.

Seasoning – Hardening and weathering affect due to evaporation of quarry sap and formation of crystalline film. 6 to 12 months for proper seasoning is essential to make the stone worth using in construction applications.

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Weathering – Should withstand rains, frost, wind and all other extremities in weather.

Resistance to fire – If free from calcium carbonate or oxides of iron, it will show considerable resistance to fire.

Durability – Compact stones are more durable.

Cost – Should have minimum cost in quarrying, transportation, dressing and installation.

DRESSING OF BUILDING STONES

The process of cutting and converting the stones to the required shape and size and to give them a smooth finish is called cutting and dressing of stones.

TYPES OF DRESSING OR SURFACE FINISH OF STONES

Scabbling dressing:The dressing in which irregular

projections of the quarried (extracted) stone are removed by means of scabbling hammer is called scabb,ing dressing.

Hammer dressing:The dressing in which the stones are

made roughly square or rectangular by means of a mason’s hammer, also known as Waller’s hammer, is called hammer dressing. When used in a wall, the roughly finished surfaces are further modified by forming to 5cm wide margin at the edges of the exposed faces.

Thank You!