Stone materials

Stone materials

1. Natural stone

   • Types of natural stone used for construction: limestone, marble, granite, slate and tuff
   • Granite
     • Igneous rock, composed of quartz, feldspar and mica. And formed by the crystallisation of volcanic magma under the Earth's surface. Very resistant: impacts, compression and erosion.  Uses: floors, walls, kitchen countertops and sculptures.
   • Marble
     • Metamorphic rock:hard and dense. Formed from limestone. Good touch and well resistance to compression and extreme weather conditions. A lot  of colours and shiny finish after is polished. Uses: make sculptures, decorations, columns, floors, walls and kitchen countertops
   • Limestone
     • Is: porous, off-white sedimentary rock( white and contain animal fossils). Used for sculptures and buildings(breakwaters) . And to produce lime and cement.
   • Slate
     • Dark blue or black metamorphic rock  formed by  compression of fine clay. Is waterproof, due to its dense and compact nature. Uses: roofs and pavements
   • Tuff
     • Porous rock formed by the cooling of volcanic ash and lava.  Good thermal insulator. In the Canary Islands,  architecture  combines tuff with white limestone.

2. Extracting and processing stone

   • Is extracted from natural deposits. Large blocks: marble and granite from quarries,it can be cut into smaller pieces. Other materials: gravel and sand, are aggregates. 
   • Stone blocks
     • Some types of stone: granite and marble, are extracted in large blocks. The blocks are cut, shaped and finished.
     • Quarrying
       • Large stone blocks are removed from the Earth´s crust using methods: controlled explosions, mechanical drilling and expansive cement. A diamond wire saw: to cut it into smaller pieces for transport to a processing plant.
     • Processing
       • The stone is processed.
       • Cutting
         • Diamond and ceramic saws, to cut the stone into smaller, thinner sheets. Wedges and presses  break the stone in pieces.
       • Shaping
         • Lathes give the stone sheets final shape.
       • Polishing
         • Machines with abrasive discs:smooth the stone.
   • Aggregates
     • Created when stone is eroded by water, wind.. They are  produced in quarries when large blocks of stone are cut and broken into smaller pieces.
     • Aggregates that come from rivers: river rock. Pieces are smooth and round, and  used for decoration and pavements. Crushed rock has irregular edges that provide more friction. Crushed rock: paths or roads and concrete. River rock, is not crushed; it is extracted  from rivers and then washed. 
     • Sorting
       • Grains are separated by size . Is  done with machines that use vibration, compressed air or water
     • Crushing
       • Grains of gravel are crushed in small pieces. Is done with jaw crushers or impact crushers.
     • Cleaning
       • Foreign objects: wood and dirt, are removed. Also washing and drying.

3. Stone binders

   • Plaster, lime and cement used as binders to hold materials together. When water is added  an exothermic chemical reaction happens. After ,they are hard and resistant.
   • Mortars
     • Mixtures of binders with sand and water. Can be: hydraulic or non-hydraulic. Uses: binding bricks, rough finishes, foundations, beams, bridges, ports and other structures.
     • Hydraulic mortars
       • Can set underwater, useful for building bridges and structures at ports. Can be made with  hydraulic lime or cement.
     • Non-hydraulic mortars
       • Set in open air.Ccan be made with non-hydraulic lime or plaster.
   • Cement
     • Is a mixture of limestone and clay that has been crushed and heated to 1,250ºC. Amount of plaster is added to mix with water to form a paste. When it dries and sets, becomes hard and resistant. Uses: cement board, pipes, pavements, bricks and blocks, mortar and mixtures with other building materials.
     • When are mixed with water, they form a liquid (slurry). Used to finish walls or pavements. Becomes fragile after it dries. Sand added for more strenght.
   • Lime
     • Produced heating limestone (calcination) to 900ºC . After is mixed with water, it forms a paste it solidifies  easily. Uses: whitewashing for walls and in mixtures with other building materials.
   • Plaster
     • Made from gypsum rock: is crushed, heated and dehydrated. It dissolves in water, creates a sticky paste that dries quickly. After, plaster is resistant to compression and fire. They will rust in contact with plaster. Uses: lining for walls and ceilings, prefabricated plasterboard for walls and ceilings, prefabricated mouldings and sculptures.

4. Artificial stone

   • Can be manufactured with binders and materials: fibre, gravel and sand.
   • Concrete
     • Mixture of gravel, sand, water and cement form a rock-like material.  Uniform grey colour and  shape of the formwork. Very resistant to pressure, . However, when concrete is used for structural purposes,rebar is added. Reinforced concrete,  resistant to pressure, traction and torsion. Uses: concrete used without rebar . Is mixed with lighter materials to fill in spaces under terraces and roof structures. To make structural elements: beams, pillars and floors. Can combined with insulation to make exterior wall panels for buildings.
   • Fibre cement
     • Composed of fibres with mortar. Were made of asbestos, but has been prohibited. Must be removed from any old buildings (pipes and roofs). Use fibreglass or cellulose fibre to make fibre cement.
   • Hempcrete bricks
     • Made of hemp fibre, soil and lime as a binder. After, is pressed in brick moulds and dry. Energy is used to make hempcrete bricks. Strong and resistant, thermal and acoustic insulation and regulate the humidity in the air.
   • Terrazzo
     • Is a mixture of gravel and white cement and is used for floors.  Tiles or poured on-site and then polished.  Uses: outdoors to make benches, fountains, window ledges and rain gutters.