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close this bookAppropriate Building Materials: a Catalogue of Potential Solutions (SKAT; 1988; 430 pages)
View the documentPreface
Open this folder and view contentsIntroduction
close this folderFundamental information on building materials
View the documentStone
View the documentEarth, soil, laterite
View the documentSoil stabilizers
View the documentFired clay products
View the documentBinders
View the documentLime
View the documentCement
View the documentPozzolanas
View the documentConcrete
View the documentFerrocement
View the documentFibre and micro concrete
View the documentNatural fibres, grasses, leaves
View the documentBamboo
View the documentTimber
View the documentMetals
View the documentGlass
View the documentPlastics
View the documentSulphur
View the documentWastes
Open this folder and view contentsFundamental information on building elements
Open this folder and view contentsFundamental information on protective measures
Open this folder and view contentsExamples of foundation materials
Open this folder and view contentsExamples of floor materials
Open this folder and view contentsExamples of wall materials
Open this folder and view contentsExamples of roof materials
Open this folder and view contentsExamples of building systems
Open this folder and view contentsAnnexes
 

Stone

General

Natural stone is perhaps the oldest, most abundant and most durable "readymade" building material, found predominantly in hilly areas. Various types and forms of natural stone can also be processed to produce other building materials.

The main stones used in building are divided into three geological categories:

1. Igneous rocks, generally crystalline, formed by the cooling of molten magma forced up through cracks in the earth's crust. It, therefore, cannot contain fossils or shells. Most common examples: granites and volcanic stones.

2. Sedimentary rocks, commonly found in layers, formed by the disintegration and decomposition of igneous rocks due to weathering (water, wind, ice), or by accumulations of organic origin. Most common examples: Sandstones and limestones.

3. Metamorphic rocks, which are structurally changed igneous or sedimentary rocks, caused by immense heat and pressure. Most common examples: Slates (derived from clay), quartzites (from sandstone) and marble (from limestone).

Extraction of rocks is possible with simple tools such as drills, wedges and hammers, but skill and experience is essential to ensure accurate cuts. Harder rocks, such as granite, require more sophisticated mechanized equipment. Natural stone can be used as quarried, ie irregularly shaped, or can be shaped with simple tools or machines, depending on the ultimate construction. The material can be used completely, without wastage.

Applications

• Rubble (undressed stone) for foundations, floors, walls, or even corbelled roof structures, in all cases with or without mortar.

• Ashlar (squared or shaped stone) for regular course masonry, window sills, lintels, steps and paving.

• Impermeable stone (eg granite) as damp proof courses; also as external cladding of walls, though less suited for low-cost constructions.

• Slate for roofing.

• Gravel and stone chippings as aggregate for concrete and terrazzo.

• Granules for surfacing bituminous felts.

• Powders for extending paint.

• Limestone for lime and cement production.

BUILDING STONE MATERIALS AND APPLICATIONS

(from United Natons: Stone in Nepal, 1977)

Type

Limestone

Sandstone

Granites

Use

Walling end Cladding

 

Walling, Cladding plinths, surrounds and steps

Composition

Largely calcium carbonate

Quartz in all mica and felspar grains in some. Bonded largely with silica or calcium carbonate

Mainly felspar, quartz and mica

Method of production

Quarried, cut to size (masoning and sawing), finish as required, eg patterned, rock faced, fair picked, fine axed, rubbed, eggshell or polished

Specific weight kg/m3

1900 - 2700

1950 - 2550

2400 - 2900

Compressive strength MN/m²

9 - 59

21-105

90 -146

Water absorption %

2.5 - 11

2 - 8.5

0.1 - 0.5

Effect of fire

All non-combustible

   

Moisture expansion %

about 0.01

0.07

none

Effect of chemicals

Attacked by acids

Resistant to most acids except calcareous types which are attacked

Resistant to most chemicals

Resistance to effect of soluble salts

Poor to very good

Poor to good

Poor to good

Thermal expansion co-efficient (per °C approximations)

4 x 10-6

12 x 10-6

11 x 10-6

Thermal conductivity (W/m.°C approximations)

1.5

1.5

3.0

Resistance to frost

Poor to very good

Poor to excellent

Good to excellent

Durability

Dependent on thermal performance, resistance to chemicals and application in construction

Ease of working

Easy to hard

Hard

Hard

Liability to become dirty

Become soiled in urban atmosphere

 

Resistant to soiling

Ease of cleaning

Fairly easy to clean

Difficult to clean

Difficult to clean

Marbles

Slates

Quartzites

Window surround, floors and stairs

Cladding sills, coping steps and paving

Cladding plinths, floors, paving and stairs

Mainly calcium carbonate

Mainly silica, alumina and iron oxides

Mainly quartz

Same as limestone, sandstone, granites

Finish natural, riven

 

2725 - 2900

2400 - 2900

about 2600

about 60

75 - 200

about 100

0.1 - 0.5

0.1

0.1 - 0.5

 

Negligible

 

Attacked by acids

Mainly resistant to acids

Resistant to most acids

Good

Good

Good

4x10-6

11 x 10-6

11 x 10-6

2.5

1.9

3.0

Good to excellent

Good to excellent

Good to excellent

Dependent on thermal performance, resistance to chemicals and application in construction

   

Fairly hard

Hard

Hard

Fairly resistant to soiling

Resistant to soiling

 
 

Difficult to clean

 

Advantages

• Usually abundantly and easily accessible in hilly regions; extraction generally requiring low investment cost and energy input.

• Immense strength and durability of most varieties of stone; negligible maintenance requirements.

• Impermeability of most stone varieties, providing good rain protection.

• Climatically appropriate in highland and arid zones, due to high thermal capacity of stone.

Problems

• Deterioration may result from atmospheric pollution, eg when sulphur compounds dissolved in rainwater produce sulphuric acid, which reacts with carbonates in limestones, causing skin formation and blisters.

• Efflorescence and spelling caused by certain salts and sea spray.

• Damage due to thermal movement of some stones, especially when fixed rigidly to materials with differing thermal movement, eg concrete.

• Surface damage due to water, which slowly dissolves limestones; or by prolonged wetting and drying of certain sandstones; or by freezing of water trapped in cracks.

• Low resistance to earthquake forces, thus likelihood of destruction and endangering lives.

Remedies

• Avoidance of using limestones and calcareous sandstones close to sources of atmospheric pollution eg where sulphur dioxide is emitted (from burning coal and oil).

• Avoidance of surface treatments that seal in salts; occasional sponging of affected stones helps to remove salts, especially in coastal areas.

• Construction of movement joints to accomodate differences between the thermal movements of adjoining materials.

• Construction details that will allow water to be removed by evaporation or drainage, to avoid frost damage or washing out of limestones.

• Careful building design, especially with corner reinforcements, ring beam, etc., in earthquake prone areas; especially avoidance of stone vaults or corbelled roofs.

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