Plaster

Manufacture of the plaster

The plaster is carried out starting from the Gypse, sedimentary rock called stone with plaster which one finds in the form of alabaster or of selenite crystals. The stone is generally extracted from mines or underground careers then cooked and then broken, crushed and ground to give the white powder of the plaster. Its manufacture requires several stages.

Extraction of the gypsum using explosives, when it is about layer with open sky: “of the careers”.
Routing since the career using Truck S: the gypsum undergoes a crushing, in order to reduce the dimension of its grains.
the gypsum is transported using a carpet towards the sifting. This operation consists in not selecting that the grains of diameter lower than 40 Misters
the gypsum thus selected is stored in heap in a room covered before being homogenized because the extracted gypsum is pure only to 90%. Also it will be mixed using a machine made up of rakes which will mix the layers of gypsum.
Always using carpet, the gypsum is led in a furnace where it will be placed in a mill where, using an endless screw, it is crushed and crushed (as in a coffee mill).
It will be cooked with 150 °C. This furnace makes it possible to make go up the gypsum cooked by the top of the furnace, while the heavier impurities, remain at the bottom.
After cooling with 60 °C it becomes semi-hydrate (the gypsum lost a Molécule water and half).

Other types of furnace exist (furnaces abutment, shaft kilns, furnaces pot, on-cooker, autoclaves,…) who give various qualities.

The plaster is then mixed in a mixer with various additions (often some for thousand):

of the Starch, to improve adhesion enters the plaster and the paperboard,
of the additives,
of the retarders to modify times of catch of the plaster…

Manufacture of a plasterboard

Use of the plaster

There exist several varieties of plaster of very different qualities. the sculptors prefer plaster with very fine grains which makes it possible most accurately to reproduce possible all the details of the model. The plaster of synthesis is advised more because it is very hard so much so that it is difficult to stripe it with the nail. It offers a high degree of accuracy and a large smoothness in the reproduction. Dryness, it can be polished using a simple soft rag. Certain plasters are proposed already tinted: color flesh, (a), imitating the stone or of another matter old. One can also employ dyes: gouache or all other coloring acrylic, to add only to water. Caution! The plaster must be imperatively preserved in a dry place or then it becomes unusable. To test it, it is necessary to waste an minor amount and to observe the time necessary with the catch and solidity, once hardened.

Mixing

It is the operation which consists in carefully mixing the plaster with water until obtaining a consistent substance, creamy and soft.

Thermal resistance

The thermal coefficient of Conductivité λ varies with the Density and the Water content. One can however retain:

λ=0,5 W/m.K for densities ranging between 1100 and 1300 kg/m3.

λ=0,3 W/m.K for densities ranging between 800 and 1100 kg/m3.

Mechanical resistance

General information

The production line of the plasterboards is spread out over 350 to 450 m, according to the mean velocity of the chain. This distance makes it possible the plasterboard to lose part of its moisture and to become semi-rigid before passing in the furnace, called drier. The plasterboards consist of two plates of paperboard which take in sandwich plaster.

The paperboard used in the manufacture of the plates is delivered in rollers of 11 km what represents a weight of 3 tons. The thickness is of 0,1 Misters They are changed every approximately two hours.

According to the use of the plasterboard, there exist various types of paperboard with classifications with the fire of M0 with M1.

Manufacturing process

Using a carpet one places the first plate of paperboard, then one comes to spread out the plaster using three exits.

The plaster is mixed beforehand with water in a mixer and its temperature is maintained to 70 °C.

The second paperboard is then posed and one lets the plate dry.

Lastly, after cooling, the plates are cut to wanted dimensions, then they are stored on pallets.

History of the plaster

Already with prehistory, the man realized that the white stones constituting the hearth of fire were exhausted because of heat.

In Egypt, the man made use of the plaster to assemble the stones of the buildings and to carry out coatings (Valley of the Kings).

As of the Gallo-Roman time, the inhabitants of Parisis knew to transform the gypsum plasters some to build their houses. They found the gypsum in the vicinity, in small careers, almost with flower of ground. The Romans, them, made use of the plaster for the coatings and the sculptures. (see “natural history” of Pline Old the).

With the Middle Ages, the man realizes that the plaster resists fire better that wood. Thus it uses it as coating of protection. With the Middle Ages, then under the Old Mode, the small careers and chalk pits were numerous but they functioned in an intermittent way. The local habitat largely called upon the plaster.

At the 18th century, Paris becomes the city of the plaster thanks to its underground layers and to the edict of Louis XIV of 1667 obliging the plastering of the houses, in interior as in frontage, to avoid in Paris the disastrous fate of London at the time of the Large Fire of 1666. At the 19th century the invention comes from the furnace to industrial plaster, which makes it possible to increase the production.
Today, the plaster belongs to our life.

In 1788, Goethe, in its description of the Carnival of Rome, described the manufacture of the Confetti, such as there existed at the time. It was made balls of plaster, carried out using a funnel. It is only starting from 1891, that this Confetti started to be replaced by its modern alternative, in Papier, that we know.

In 1822, a career with plaster is created by Pierre-Etienne Lambert with Cormeilles-in-Parisis. As from 1878, Jules-Hilaire Lambert industrializes the production. The “plaster of Paris” acquires its fame.
In the Years 1930, with the Brothers Lambert, the operating cycle is complete.
The career of Cormeilles is the only one in France to feed at the same time the manufacture of the plaster, bricks, hydraulic lime, and artificial cement by the use of the matters of “discovered”: clays, limestones, marnes. The Lambert career is the greatest career of Europe with open sky.

Nowadays, the plaster is also obtained starting from gypsum of desulfurisation.
BMLithography, about 1860: The Soubise father. Friend of Jacques Master, Founder of the busy Companions Carpenters of the Duty, the Roofers and the Plasterers.

By their conquests, the Romans largely will diffuse the plaster in all the Empire. The walls of the dwellings are whitewashed with plaster and, the made ceilings of wood and plaster. It can be useful in masonry to link the stones the ones with the others. The Roman craftsmen develop also his employment like external coating: let us tons hot of red blood stone come from a mixture of finely crushed bricks, pozzolana, plaster and water. The stucco, fact of marble plaster and powder, is used with glare for the ornamentation of the buildings.
The invasion of Gaulle by Jules César gives to the plaster root in our country. The Romans, tireless builders, bring to the Celtic populations new processes of construction in masonry and plaster.

In Lutèce, on the edges of the Seine, the huts of the tribe of Parisii make place at more solid buildings. The site is privileged by nature, because the hill of Montmartre abounds in gypsum. Flagstones, gypsum blocks, columns, sarcophagi… several vestiges of IIe and IIIe century of our era testify to a “first age of the plaster” in Paris.

Gypsum with the plaster

The plaster is obtained by cooking and crushing of the “stone with plaster”, the gypsum, sulfates calcium with two water molecules (CaSO₄ (H₂O) ₂). During geological times, this mineral settled in the sedimentary basins by forming thick more or less deep layers. The extraction of the gypsum is done in careers with open sky or in underground galleries. Crushed, cooked in furnaces, it is finally crushed finely to obtain the powder plaster. This white powder with the property to harden very quickly when one mixes it with water: it is the phenomenon of the catch.

The cruel fall of the Roman Empire and invasions involve for long centuries the decline of stone constructions to the profit of woodens building largely used by the people of the North and the East of Europe.

So at the first times of the medieval Occident the plaster regresses, it knows in the South of the Mediterranean a remarkable blooming, supported by the Arab conquests. Moslem civilization indeed abundantly used the gypsum and undoubtedly marked one of the tops of the art of the plaster; in a universe where wood is rare, this one makes it possible to multiply the decorative reasons for the mosques, madrasas (religious schools) and palate. Undoubtedly one finds his more beautiful illustration in Alhambra de Grenade where galleries, walls and ceilings are decorated of a profusion of geometrical arabesques! A very engraved exubérance that one must with plastic qualities of the plaster. To the Middle Ages, the large builders who are the monks of Cluny and Cîteaux give to the honor the use of the plaster, of which the use is spread again.
The profession chalk pit organizes and codifies its activity in the capital. The Book of the trades, ordered by Louis IX with the provost of Paris, is the text founder of many corporations at the 13th century. The word plasterer then indicates that which carries out the extraction and the cooking of the gypsum, i.e. the manufacturer.

Implementation

Plasterer
Staffeur stucco worker
Plaquiste

Useful works

"techniques and practical of the Staff " of g.rondeau, s.rondeau, let us m.pons Editions Erolles.
" techniques and practical of the plâtre" of j.festa Erolles Editions.
" plaster: walls, forms and volumes" of j.c bidaux Editions Erolles

External bonds

Plâtre.com : Site on the plaster with particular applications and an encyclopedia
platrierstaffeur.com: A site with illustrations and a description of the trade of plasterer
''' exploitation of the gypsum and the manufacture of the plaster '''
lesindustriesduplatre.org: All on the plaster - industrialists of the plaster

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