GYPSUM EXTERNAL RENDERINGS OF PARIS: HISTORY AND FABRICATION

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GYPSUM EXTERNAL RENDERINGS OF PARIS:

HISTORY AND FABRICATION

Tiffanie Le Dantec

To cite this version:

Tiffanie Le Dantec. GYPSUM EXTERNAL RENDERINGS OF PARIS: HISTORY AND FABRICA-

TION. Further Studies in the History of Construction: Proceedings of the Third Conference of the

Construction History Society, 2016, 978-0-9928751-2-1. �hal-01611366�

EcUted by

James W P Campbell

NiebolasBm

Mlebae1Drlver

Mlebael Beaton

Yltln8Pan

Mlebael Tutton

Christine Wall

David Yeomans

Published by The Construction History Society 1 Scroope Terrace Cambridge CB2 IPX

www .construction.co.uk

© 2016, First Edition ISBN 978-0-9928751-2- I

Copyright© by the Construction H istory Society

Ali rights reserved. These proceedings may not be rcproduced. ln whole or in part, in any form

without permission from the Construction History Society

Formatting and layout by Yiting Pan First printed by Lulu print on demand for the Construction 1-1 istory Society

Proceedings of the Third Construction H istory Society Con ference edited by James W P Campbell, Nina Baker, Nicholas Bill, Michael Driver, Michael Heaton, Yiting Pan, Michael Tutton, Christine Wall and David Yeomans

TIIE Ti IIRD ANNlJ/\L CONSTRUCTION HISTORY SOCIETY CONFl·:Rl·:NCI·:

Organised by:

The Constructi on H isto ry Society

Hosted by:

Q ueens' Coll ege, Uni ve rsity o f Ca mbrid ge

&

The Departm ent o f Architecture, University o f Cambrid ge

Organising Committee

C ha ir: Jam es Ca mpbell

Michae l Heaton

Jonathan Lee

Yiting Pan

David Yeomans

Scientific Committee

Chair: David Yeomans

Antonio Becchi

Ja mes Ca mpbe ll

Simon Pepper

Robert Thorne

Chri stin e Wa ll

Editorial Committcc

Cha ir: James W P Campbell

Nin a Baker

Nicholas Bill

Michae l Dri ve r

Mi chae l Hea ton

Yiting Pan

Mi chae l Tutton

Chri stin e Wa ll

David Yeo mans

T(ffanie le Dantec

Gypsum externat renders of Paris: history and fabrication

Tiffanie Le Dantec

Laboratoire de l'école d' Architecture de Versailles /Laboratoire de Recherche des Monuments Historiques, Université Versailles-Saint-Quentin. Paris

Introduction

/\ rcscarch prograrrnm: slarlcd in 2015 wilhin the Laboratoire de Recherche des Monuments Historiques (l ,RM 11) aimcd al a bcllcr undcrslanding of a vcry common malcrial li:iund on the facadcs or hislorical buildings in Paris and ils surroundings: gypsum rcndcrs. The rcscarch programme aims on one hand lo cslablish the true matcriality ofgypsum rcndcrs and lind a way lo rcplicalc il or lo rcpair il bcllcr; and on the olhcr hand, il aims for a bcllcr undcrstanding of the history of thcsc rcndcrs and of the design of the Parisian lacadcs.

The gypsum cxlcrnal rcndcrs of Paris arc wcll known by the archilccls carrying oui thcir resloralion and by the city administration working on thcir conservation. l lowcvcr, nobody agrccs on the composition of lhcsc ancien!

gypsum plaslcrs, lcading 10 nurncrous pathologies artcr ill-carricd rcsloralions. Whal cvcryonc agrccs on, howcvcr, is lhc gcncral slrcnglh of this old malcrial lo rcsisl wcalhcr crosion. Somc rcndcrs arc centuries old whcn rcsloration work bcgins.

Why wcrc thcsc lraditional rcndcrs so rcsilicnt? Was il the way the gypsum was produced? Was il the way masons uscd gypsum on the lacadc? Was il the way the facadc was dcsigncd? Or was il a combinalion of ail thosc rcasons? This article will shed somc lighl on lhcsc questions.

To writc this article, historie wrillcn lilcraturc was comparcd wilh a corpus of facadcs with gypsum rendcrs and nurncrous visits or ruincd buildings and rcsloration work. /\ gcographical and historical rcvicw will sel the conlcxl lirsl. Thcn fabrication or 'Plastcr of Paris', ils application and architectonie details will be analyscd 10

clcar up the myslcry of ils slrcnglh.

Ceography: the gypsum arca

Thcrc arc two main arcas in France whcn: gypsurn is liiund casily, close lo the surface and rcady to be cxlractcd:

the rcgions of Paris and Provence. Thosc Iwo rcgions have a built hcritagc or gypsum clcmcnls, mortars and internai or cxtcrnal rcndcrs from the (,allo-Roman pcriod until the beginning of the twcnticth ccntury.

ln the rcgion of Paris, the use ofgypsum in construction is linkcd to the acccssibility of the raw matcrial, casier lo rcach in the norlhcrn pari lhanks to oulcrops, the most famous or !hem being Montmartre and Belleville, whcre gypsum has bccn cxtractcd since the lirsl centuries

/\.Dl

1

1 -

Far from following the boundaries or the administrative rcgion or llc-dc-1:rance, the arca of gypsurn use can be obtained (Fig. l) by looking al buill heritagc

59

Gypsum externat renders of Paris: history andfabrication

and vcrnacular architecture past and prescntl 21- 1 n culturally distinct arcas with a strong local tradition of building with gypsum -such as Parisis, Goële, Multien, Orxois and Bric Française - gypsum outcrops widcly.

/ /

'

Legend

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Fi3J;3=::::~n

_...:...,..~1~ .21Xl1J

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Figure!: the gypsum area around Paris (Tiffanie le Dantec, 20/6)

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The region's three major rivers, Seine, Oise and Marne, wcrc also convcnicnt for sprcading the use of gypsum in construction. 1--fistorical urban centres with gypsum facades arc a common sight ail along thcir banks as far as Rouen, for the river Seine, where the historical city centre fcatures gypsum-rendcrcd facadcs. Furthermorc, the spherc of influence of, for instance, Paris through the cxporting of gypsum along carriagcways from Montmartre is likely to have been the radius of around thirty kilomctrcs around the city that could be covered by horse carriages within a day.

History of gypsum in architecture

Antiquity,from thejirst to the third century A.D: prefabrication.

Gypsum was uscd for construction as far back as the first ccntury A.D: roof and wall tiles, bricks and ornamental elements have been found during archaeological excavations in the location of Gallo-Roman Lutecej3] (5th arrondissement of Paris). Thcse were prefabricatcd elements, but according to the Greek author Thcophrastus ('On Stones') and the Roman author Pliny the Eider ('Natural l listory, XXXVI 13ooks'), gypsum rendcrs were common in the Roman Empire, al least for internai finishcs.

Middle Ages,from thefifth to the thirteenth century A.D.: new materials

The barbarian invasions wcrc a period of intense migrations throughout Europe. The ncw Frankish population brought its own techniques for building: timber structure with cob on woodcn latticcs/41-The Roman stonc and gypsum masonry faded into history as the Roman Empire collapscd.

60

T(/Janie Le Dantec

Middle Ages, from the thirteenth to the sixteenth century A.D.: gypsum renderings

The use or gypsum rendcring instead or coh on wooden lattices started, in France, around the thirtccnth century.

Severa! rcasons arc proposcd for the change. The urban dcnsilication of the lcrt bank of the river Seine covered up the extraction sites for stoncs, mud and sand originally locatcd therc. At the samc lime, the growth of the city on the right bank and ils extension to the North made the construction sites closcr to gypsum quarries and production areasl 51. Gypsum was thcn choscn for ils proximity to the ncw parts of the city.

A contemporancous scholar, 13artholomcw The Englishman, tcstificd the widc use or gypsum in Paris in 1372:

« ... où es/ le plâlre en grand.foison, lequel est comme verre quand il est cru, et dur comme pierre. Et quand il est cuit el détrempé d'eau. il se convertit en cyment, dont on fait les parois des beaux édifices el les parrements des maisons »161. (" ... whcrc gypsum is plcntiful, bchaving likc glass whcn raw and as hardas a stone. And whcn it is baked and soaked into water, it convcrts to cernent, from which we makc the walls of the bcautiful buildings and the facing of the houses." Translation, Le Dantec)

1667: King Louis XIV's order

In I 666, the Great Fire engulfcd the woodcn city of London, dcstroying most of it. Louis XIV feared the same would happen to Paris as most of the buildings wcre still composed of timber structures. In 1667, the 18^th of august, the King ordered that ail buildings must be covercd with gypsum plaster, on the inside and on the outside, to prevent tire. The same law forbadc corbclled constructions and gave a maximum height for facades. Owners not obeying would face fines and the destruction or their house. Thanks to this, Paris did not burn and the Golden Age of gypsum rcnderings bcgan.

Sixteenth and seventeenth centuries: the golden age

Following I 667, the city covered itself up with gypsum. Paris was then the largest and most populated city of the western world, experiencing huge urban growth and much construction. Contemporaneous authors spoke of a city where I 5 out of 16 houses had gypsum facades[7], and whcre three quarters of the hôtels particuliers werc also made of gypsum, encompassing a wide band of the social strata. The use of gypsum was not only for externat and internai renders, but also for mortar, filling of half-timbcring structures, fïlling of timber partition walls, chimney duels and stacks, floor slabs, stairs and ornaments.

The use of gypsum in cvery elcmcnts or construction in Paris was widcly dcscribed by authors from the seventeenth century until the ninetecnth ccntury:

"Le plâtre est si utile el si employé dans la construction de nos maisons, que, par l'éclatante blancheur dont il les revêt. il fait de Paris une ville de plâtre. C'est à celle matière froide qui brave les atteintes de la flamme que noire cité doit sa tranquillité contre les accidents du feu. "

Raoul Boutrays, Lutctia, 161 1

61

Gypsum externat renders of Paris: history and.fàbrication

("Gypsum is so useful and so much used in the construction of our homes; ils dazzling whiteness adorns thcm and makcs Paris a city of gypsum. To this cold malter dclying the wralh or the !lames, our city owcs ils quietncss against tire accidents." Translation, I.e Dantec)

« Â Paris el dans ses environs on en fait une immense consommation pour construire les maisons. (. .. ) de manière qu'un bâtiment. depuis le sol du re-de-chaussée jusqu'au grenier. peut être emiêrement recouvert de plâtre. et paraître composé d'une seule pièce de cette matière. »

J. Claudel cl 1.. Laroque, l'raliquc de l'J\n de Construire, 1850. p77

("Thcrc is such a huge consumplion lof gypsuml in Paris and ils surroundings to build houses ... thal a single building, from the ground Jloor to lhe allie, might be covcred with gypsum, and secms to be made hy a single piecc ofthis material." Translation, I.e Danlcc)

Nineteenth centwy: industrialization

The lirst scicntific investigations of gypsurn wcrc of Antoine Lavoisier during the cightccnth ccntury, thcn I lcnri Le Châtelier du ring the ninctccnth ccntury. They hclpcd dcvclor undcrstanding of rroccsscs such as the calcining of gypsurn, the rnixing, and the sctting. l .avoisicr wrotc the limnula of plastcr hydration, a rroccss known as rnixingl81:

CaS04, l /21120 + 3 /2 I Il)---> CaS04, 21120

(Plaster powder) (Water) ( Gyps 11111)

A bctlcr undcrstanding of gypsurn, lcd ¹⁰ a more cflicicnt way to producc it. The lirst machines to grind it and calcine it wcrc designed as soon as the end of the cightccnth ccntury to producc a thinncr powdcr, a whitcr product. The lirst furnaccs and grindcr wcn,; uscd in the middlc of the ninclccnlh ccntury and largcly sprcad in f'actorics by the bcginning of the twcnticth ccntury. lndustriali,.ation of the scctor li)llowcd the galloping urbanization of Paris and ils suburbs, with a highcr dcmand for gypsum for cvcryday construction. An author compares production of plastcr during the ninclccnth ccntury wilh the production of brcad: 'le plâtre n ·est pas. à Paris. sans analogie avec le pain. Paris a besoin chaque matin. de sa ration de plâtre.Fais.

191

("ln Paris, gypsurn plastcr is 1101 without comparison with brcad. l:vcry morning, Paris nccds ils frcsh brcad suppl y." Translation, Le Dantec)

Thcsc ncw ways of production and use of machines slowly changcd the matcriality of the powdcr (Fig.2).

62

Gypsum-madt' bocks. t1\~ and O,•).)n'\o,'f\lS

'-'\asonry repl.Kt"d by t,mber s'.ruotHe

,mdcob

Gyp,,;um foc"lldf.'<U)(JS repki~t'(ob

- ! == _·I

Tiffanie Le Dantec

lnrl11,;:1r,1!i,.::irion of Golden Ag~ of J)l'oducttor.

gyJ}'>urn 1n gyp-,vn, plast.01

(Q115,t1u,..t1on :Jowty1:.han9€d

100 soo IÙ()() 1200 1667

(1AUO ROMAN MIGRAllUN

LUTF(F PfRIOD

U IV~ t Xl'ANSJON ro

\IORTH

1 K11l(J t 0111s X'IV ~ o,der gypmm plastc-ron rm1bc1 Hru1,,.nue

Figure 2: Timeline. hislorv of'f!J'/J.1·11111 a round Paris (Tiffanie Le Danlec. 20 I 6)

Twentieth cenl11ry: crisis

fnd of t1;,w:!1t on·

nal technique~

Bcl'orc the First World War, France was the princiral cxrortcr or gypsurn and the rrincipal produccr. The quality or the "Plastcr or Paris" was known worldwidcl 101. i\ lier the war, gypsum in France did not adapt to the ncw market of building construction. The building construction rcquircd less comrctcnt workcrs, lcss ornaments, a bcttcr pacc ... The rnason or Paris, a highly ski lied worker, was suddcnly not uscl'ul anymore and was rcplaccd by migrant workers between the two wars. The masons tricdl 111 to change thcir material by using additives to slow the sctting down and to incrcasc ils rcsiliencc but thcsc chcmicals wcre not monitored and vcry olicn lcd to the ruining or the racadcs. i\rchitects and cnginccrs no longer trustcd gypsum plastcr and stoprcd using it in construction.

The job cvolvcd to bccomc a singlc-taskcd one, making the internai rcndering oraparlments becamc the daily lifc or plastcrers. This job was cxhausting and olicn subjcct to mockcry as it was dirty and dusty, workers coughcd and thcir body cndcd up crookcd by the rcpcatcd contortions ncccssary l'or plastcring ccilings. Thcrc is a song by Cavanna in the l 930's lhat gocs: "("es/ le bon plâ!re de paris. Qu 'a/àil crever 111011 mari" ("The good plastcr or Paris causcd my husband's dcath." Translation, Le l)antcc).

From thcn until now, gyrsum rlastcr has had a bad rcrutation and being a plastcrcr no longer attractcd young rcoplc. Gypsum cvolvcd and bccamc rlastcrboard in the l 960's, rclcgating wct gypsurn plastcr to rcstoration works.

Traditional making of Plastcr of Paris

l'lastcr or Paris is a product obtaincd alicr calcination or gypsum stoncs in furnaccs. The making of Plastcr of Paris l'ollows live stcps: extraction, calcination, grinding, transportation and storagc.

This article rocuscs on the timclinc bctwccn 1667 and 1950 as traditional ways or producing plastcr or Paris carricd on quitc latc. The stcrs dcscribcd bclow tcstily to skills cxisting centuries bcl'orc 1667 which slowly cvolvcd during industrialization from the 1850\ until the l 950's.

63

Gypsum external renders of Paris: history and fabrication

Extraction

Gypsum is a common minerai, calcium sulphatc dihydratc (CaS04·21120), round in four strata within scdimcntary rocks in the Paris Basin. The three first strata arc rcachablc thanks to outcrops shapcd as hills:

Montmartre, Belleville, Chaumont, Ménilmontant, and Charonne. Extraction of gypsum blocks was done in opcn-cast (fig.3) or underground excavations. Il is worth noting that any owncr with gypsum outcrop located in his lot could extract it and sell it in his own namel 12]. The owncrs of quarrics wcre thcn round in any social group from peasants and craftsmen to mcrchants and noblcmcn and any institution. Gypsum was round casily and did not nccd any particular cquipmcnt to be cxtractcd and sold. This cxplains why a map of past quarrics has ncvcr been done, somc quarrics being just a holc in the ground.

Figure 3: Quarries around Montmartre Hill (Paris en I 672 : fac-similé du premier plan de Jouvin de Rochefort, impr. Ch.Chardon aîné, 1870, Bibliolhèque nationale de France, département Cartes el plans,

GESH l8PF37DIV3P60)

Roughly-cut blocks were extracted by the quarry workers and taken to the furnaces. Depending on historians and centuries, furnaces were located on the site of the quarry or on the construction site. Transportation of calcined gypsum from the quarry to the construction site could alter the material, so building workers preferred to heat it in the city. On the other hand the smoke was irritating and many complaints pushed the city to forbid furnaces[ 13]

several limes in its history.

Calcination

Gypsum stones must be heated to a tcmpcrature of l 30°C so the calcination proccss occurs:

CaS04, 21120 -3 /2 1120 ___, CaS04, l /21120

(Gypsum) ( 1, 5 water) (l'lastcr of Paris)

This low temperature, compared to calcination of lime (800°C), makcs producing plaster casier.

64

Tiffanie Le Dantec

From the cightccnth ccnturyl 141 to the 1950's, a type or f'urnacc callcdfour culée was used to hcat gypsum. The simplicity ofthcsc furnaccs and thcir similarity with brick f'urnaccs uscd by the fourteenth centuryl 151 may let us think that they werc uscd al the end of the Middle-Ages but wc Jack cvidencc. The stones were placed in a shed composed of thrcc walls otlcn made or gypsum stoncs and mortar with a high open gabled tiled roof. The stones werc laid from the biggcst to the smallcst of top, in rows dividcd by vaulted holcs where wood would be burncd. (Fig.4). The hcating proccss lastcd around 12 hours: the stones becamc white as the water cvaporated producing a thick smokc. Once cold, the furnacc is dcstroycd and the stoncs put aside to be ground.

Figure 4: Tradilional furnace and de/ails of the layout of gypsum blacks. left: Four à plâtre (Argenteuil), Paris, Hachette, /932. Righi: A gypsumfurnace, Noisy-le-Sec, 1925, Photo Auguste Robin, Larousse, 1925.

Grinding

Traditionally, sincc Theophrastus to the bcginning or the ninetcenth century, grinding was done with a wooden staff, hitting the calcined gypsum blocks for l10urs, hcnce the still in use expression: battre comme plâtre (being beaten very hard). This exhausting job changcd during the nincteenth century with the use of the animal-powered and then mechanical grinder, which made a much fincr powdcr. Masons would complain as soon as the 1850s' saying that plaster came to the building site too fine and not suitable for construction[ 16].

Storage and transportation

Plaster produced on the quarry endcd upas a rough white powdcr. Calcined gypsum spontaneously hydrates itself using the moisture in the air. Once calcincd and ground it should be used within few days or il is called éventé (stale) and unsuitable for building. lt can be stored in sealcd barrels and moved with carriages but this way of transportation must not have bccn protcctivc enough as gypsum plastcr was not exported very far. Un-burnt stones were also exportcd to be hcatcd whcre nccded, but workers there lacked the skills to burn thcm wcll to make a good plaster and this solution did not lcad to exportation either.

What is Plaster of Paris?

According to the dirtèrent stcps wc have just followcd, wc have a clcar dcfinition of what Pl aster of Paris powdcr comprises:.

65

Gypsum external renders <4Paris: history andfabrication

Gypsum : in at lcast four di ITcrcnt forms according to the tcmpcraturc the sternes wcrc at and thcir proximity to the namcs:

Undcrburnt gypsum ( < l 30°C) l lcmihydratc a and

p (

130-150°) Ovcrburnt

Anhydrite 111 (200°C) Anhydrite 11 (220-350°C)

Calcium carbonate: rcsulting from or having scdimcntary rocks (limcstoncs) cxtractcd at the samc timc as gypsum. Quarrics had di llcrcnt amount or calcium carbonate in the gypsum strata, from 3 to 13% (Table. 1 ).

Coal and ashcs: rcsulting from the burning orwood. Workcrs tcstilicd that rcplacing wood by coal or bituminous coal did not providc a plastcr suitablc for construction.

Quartz and silica: rcsulting from dusty quarrics, and bcating on the ground ... A wcalthy owncrl 171 or quarrics as soon as the cightcenth ccntury complaincd that the dirtincss or his quarrics and his workcrs would spoil the gypsum plastcr.

Lime perhaps, irthc tcmpcrature in the furnacc rcachcd 800°C.

Di llcrcnt studics wcrc donc as cari y as the ninctccnth ccntury (Table.!) and more rcccntly to clcarly say what gypsum plastcr comprises. The studics agrcc on saying that thcrc is hctwccn 4 and 20% or calcium carbonate, a bit of quartz (not always), a bit or silica, somc oxidcs, picccs or coals (l·ïg.5) and the rcst is gypsum.

Table /: Gypsum p/as/er exhibiled al lhe 1878 Exposilion universelle in Paris. ln. Gus/ave Os/el. Cours de cons/rue/ion. Ma!ériaux de cons/rue/ion el leur emploi. Paris. 1885. Archives du Musée du Plâ!re

Caldum C11ldtLm ^:\bgnuiu

:'\,Ullt oftht _sulphate tarbonatt "'

r:y~wn plastn

.. ..

carbo

_..

nalt

Vary ¹09 10 2 5 03

\ïtry 72 6 12 5 ~,

Romainville s, 1 24 27

\ïllejuif 77 95 S 5 I 9

Bondv 79 os 99 23

Boadv S3 4 69 ' ^{_ )} ' B-Le Comte 83 15 4 3 0

Lamarche SS 45 3 '5 0

Bussieres 84 ï.15 04

:\lo~·enoe S0.87 7.23 2.23

Aturoi.ri.ium oi:jd~ abd ftrrou.s puoxidt } 5 :! 7

os

06

J 5

0 35 0 0 4)

l.l

66

l.asolublt

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49

li'

06 H 4 4 24 1 2 1 6 I 05 2.-4

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H5 nornnl 3 53 fi.nt

5 S nonnal 6 !5 nonnal

; SJ normal

4 fine

64 normal

6 ~ nonnal 6 95 normal 5.71

Tiffanie le Dantec

Figure 5: Two layers of rendering. charcoals and unhurnl gvpsum can be seen on lefi. Théâtre de la Renaissance.

Paris. Binocular macroscope. (photography .Jean D11casse-Lapeyr11sse. LR MH. 2015)

We also ean conclude that plastcr or Paris was a vcry rough powdcr, barcly a powder at ail judging by comments from nineteenth ccntury masons who had to beat the plastcr into picccs again on the construction site! 18].

lt is important lo mention hcrc that limc-basccl mortars wcrc also uscd al the timc in construction, but gypsum mortars wcrc usccl cvcn more in vcrnacular architecture. The priccs for limc-basccl or gypsum-basccl plastcr wcre roughly the samc according to treatiscs from cightccnth ccntury, but as gypsum mortar would have a quickcr setting lime, workers would choose it. Conccrning rcnclcrs, thcrc arc only gypsum-basccl renclcrs in the rcgion or Paris; thcrc ne ver wcrc I imc-basccl rcndcrs.

Traditional application of gypsum externat renders

Masons and plastcrers lcaturc in the book by !·:tienne Boileau! 191 dcscribing ail the statuscs or proressions in Paris from 1254 lo 1271. l'lastercrs wcre the workcrs cxtracting and hcating gypsum white the gypsum plaster was usccl by masons. A hicrarchy or apprcnticc, companion and mastcr masons usecl il to build an entirc building from scratch.

Material preparation

Yocahulary orgypsum plastcrs: grinding and sererning on site

The masons usccl gypsum plaster straight out or the barrel orjute bag. They sercenecl it using two differcnt sicves:

a basket proclueing plâtre au panier (basket plaster) and a horsehair sicve eailcd sas and producing plâtre au sas (horschair sicve plaster). The basket had largcr holes than the horschair sicve and produecd a roughcr gypsum plastcr.

Workcrs couic! also make a thinncr plaster throwing gypsum plastcr in the air with a spaclc: the layer or plastcr stuck lo the spadc is cailed .fleur de plâtre ( llowcr or plastcr). Anothcr type or plastcr was macle putting pl aster from the barrel through the basket then through the sas: instcad orgetting the thin plastcr out or the last sieve, the workcr wiil takc the plaster on top or the horsehair sievc, which is cailcd crépis.

67

Gypsum external renders of Paris: history andfabrication

Masons created the type or gypsum plaster they needed by beating the gypsum and sereening it. These operalions led to gypsum plasters with extremely different granularity.

Mixing plaster.

The mason gently sprinkled the gypsum powder on water until they merged and then mixed il with his trowel to obtain a paste. The amounts or water and plaster also depended on which type or paste the mason needed.

Usually, a normal paste for a gypsum rendering would conlain halrplastcr and halfwater. Masons put lcss water to have a more resilient plaster with less porosity and a quick setting: uscful for joints. They put more water into the paste for pouring gypsum plaster into cracks and for some layers or rendcrs.

Application of gypsum externat renderings jollowing treatisesfrom the seventeenth. eighteenth and nineteenth centuries

Treatises[20] from 1691 until 1885 have been used to develop this mode! of traditional application or gypsum renders. This is how it was done before industrialization ehanged the material too much and before the knowledge orthis manner of production and use disappeared. The application followed these steps:

The wall, either made of rubble stoncs, bricks or timber-framcd structure with stonc, brick, or gypsum fillings should be brushed and soaked with water the day before the rcnder is applied. Timber lintels and structures should be riddled with nails or grooved for a better bonding.

Renders should never be applied in tempcraturcs bclow 5°C or ovcr 35°C, or when il rains.

Ornamcntal foaturcs (mouldings) were always made beforc the rendcrs wcrc applicd.

The gypsum rendering was composed of four laycrs depending on the statc of the wall (Fig.6):

Renformi: if in a bad state, the wall was put back in shape to insurc ils natness. A compact gypsum paste was made to fill the ho les and make the joints. Bumps were plancd off.

Cobetage: A quite nuid gypsum paste is cast upon the wall with a wide brush, quiekly the mason unified the layer with his hand. The layer is left to set.

Crépi: A quite compact paste is made with the crépis, the lcftovers of gypsum on the top or the horsehair sieve. This gypsum plastcr was east on the wall with a brush, a trowel or the hand. The layer was then unified quickly with the back of the trowel. A Berlhelée trowcl was then used to groovc the layer with its toothed side.

Enduit: i\ more nuid paste is made for the final layer with the plaster from the horschair sieve. lt was cast and sprcad with a trowcl. Then, when the plaster sel, the layer was cul with the sharp side of the Berthelée trowcl in ordcr for the whole wall to brcathe.

Altogether, the layers can reach a thickncss bctween 5 and 12 cm.

68

Tiffanie le Dantec

Figure 6: Goussainville, nineteenth century house. Left: general view. Righi: detail on the layers of the rendering.

(Tiffanie Le Dantec, 2015)

Each layer then had a differcnt porosity and a diffcrcnt granularity. Rcsearch has still to be done to fully understand the way the layers work togethcr to let the wall breathe: how is the moisture transfer insured from the wall to the outside but not the other way round.

Toward a gypsum architecture?

Gypsum plaster has many qualitics. lt is breathable; il helps moisture exchanges; it is firc-proof; and il is plastic.

lts plasticity, in particular, allows it to accommodate seasonal movement of timber or stone structures. Il has a good 'bounding', i.e. during setting, gypsum plaster expands and will fill ail the voids and holes in the support.

And it has good thermal insulation and soundproofing qualities, thanks to ils porosity. But these qualities are nowadays overshadowed by a disadvantage: ils solubility in water.

Features for avoiding water jlow

Scientists working on the rescarch programme will tell us in the coming years how the materiality or the application ofthose ancient gypsum plastcrs fought solubility. The design of the facade is also very important for avoiding rainwater flow ovcr the facadc. Moisturc is nol so much of a problem as long as it can dry. The rcal danger is a constant water flow slowly dissolving gypsum. Centuries of use of gypsum plaster architecture in the area of Paris have allowed masons and architects to solve the problem and led to facades being able lo survive decades without damage.

ln ordcr to prcvent the dissolving of the facadc, somc architectural fèatures wcrc necessary to resisl water ingress:

69

Gypsum externat render. , · o f Paris: history andfabrication

Rainwatcr flow: mouldings on the J'acadc insurcd that flowing water die! not wash the facadc away, hut cncouraged formation or drops that would fall to the ground. Comices on top, string-courses at cvcry floor, and cxtcrnal window frames arc part of thcse J'caturcs.

Water splash: whcn thcy mcct a plane surface, raindrops throw other smaller raindrops around, causing dissolving of the rcndcr. This was prcvcnted with a metal (lcad or ,.inc) shcct ovcr the string-courses and a di fièrent matcrial for the hase.

Capillary risc: water J'rom the ground riscs through the foundations or the building and exits the wall, going through the mortar, joints and rcndcrings to gct out. This water is ollcn in liquid form and cause damages to gypsum plastcr.

Rain

Paving-stones on sand

Natural drainage system

Ground water·

cap,llarity rise

~

Hot air and steam

~ =

1 ~

Figure 7: Cycle of water thro11gh seasons inside a .1·/one wa/1 with gVfi.\'/1111 renderingv (Tif/émie Le Dantec. 2015)

Conclusion

The long lost strcngth or gypsum cxtcrnal rcndcrs was ccrtainly duc to the hctcrogencity or its composition, the highly ski lied savoir~/àire or the masons who knew, aller live centuries practising gypsum plastcr, how to makc it last longer. The design or the l'acadc, skil l'ully avoiding water llow on the surface or the rcnders also adds to what one can considcr gypsum architecture.

The aim or this papcr was to expose the lirst clcments or rcscarch on the gypsum cxtcrnal rendcrs or Paris. lts aim was also to ask questions, to tic ahlc to carry on rcscarch in this direction through the thesis and through the rescarch programme led hy the LRM 11.

70

Ttffanie le Dantec

Among many questions, the main one is: how ean people trust gypsum plasler again? A lier 100 years of dcspising plaslerers and having a low qualily material, how ean young apprenticcs be made willing lo practisc this job once aga in and carry on the lcgacy of the ski lied masons of Paris?

Acknowledgements

LRMH team: Jean l)ucassc-Lapeyrussc l'hl), LRMII civil engincer; Véronique Ycrgès-Bclmin, I.RMII rcscarch cnginccr and Pôle Pierre rcsponsiblc; Stéphanie Celle, heritage architecl, LRMI I depuly director.

Léa V team: Nadia l loycl, architecl, l'hD supervisor

Fondation des Sciences du Patrimoine: l·:mmanuel Poirault, direclor

livan Chakrol{ architecl and author.

Notes and references

l

11 Association des C,éologues du Bassin parisien, «Les anciennes carrières de Paris cl leur consolidation» in. Les Ruches au service de l'Homme. Géologie el préhistoire du Bassin parisien, Bulletin d'information des Géologues du Hassin parisien, Mémoire hors-série 11°7, publié avec le concours de Gaz de France, 1989, Condé-sur-Noireau

121 Thiébaul, I'., La maison rurale en lie-de-France, l·:yrolles, 2001

131 Robin, S., Philippe Marquis, · Aux origines du plfüre de Paris'», Le Plâtre. /'Art el la Matière. Créaphis, 2002, p.89

141 Talé, T., Historique du Plâtre, Congrès Technique International de la Maçonnerie et du Béton Armé, 1928

151 Robin, S., Philippe Marquis, op cil, p.89

161 Barthélémy L'Anglais. De 11roprielatitus rornm. n.d.

171 Fcrroussal de Castel bon, l·:.11., Réflexions sur la mauvaise qualité du plâtre el sur sa cause, Paris, 1776 181 Lavoisier, M., Mémoires de Mathématiques el de Physique. présentés à l'Académie Royale des Sciences. par

divers savants el lus dans les assemblées. Tome cinquième. 1768 p.341

191 Canet, M.M., 'Quatre générations de plâtriers dans le nord-ouest parisien, ruptures cl continuités à la plâtrière Yicujol', Le Plâtre. /'Art el la Matière, Créaphis, 2002, p.47-57

1101 Gilardi,I'., Le plâtre. ses caractéristiques essentielles pour la construction, 1933, Archives du Musée du l'lfüre

1111 I:ncyclopédie des Métiers, La plâtri'/'ie. le Swffet le Stuc, Yol.2, l .cs Compagnons du Devoir, 1994 1121 Guini-Skliar, A., La 11ierre à bâtir dans l'architecture parisienne, Tours, 1998

1131 I.e Roux, T., 'Des li.lUrs à plâtre dans l'aris, l listoirc d'une parenthèse conllictuellc, 1765-1800', Les Articles du Musée du Plâtre, 201 0

1141 Diderot cl d'Alembert, Recueil de Plonches sur les Sciences. les Arts libéraux el les Arts mécaniques, Paris, 1751-1772, l·ïg. 1

l

151 Lal~trgc, 1., Le plâtre dans la con.,·trnction en lie-de-France: techniques. morphologie et économie avanl I ïndustrialisalion, l'h.D. Thesi, Université Paris I Panthéon-Sorbonne, 2013, p6 l 3.

1161 Claudel cl l .aroquc, Pratiqul' de /'Art di' Construire en Maçonnerie, Paris, Carilian-Gocury et V. Dalmonl,

71

Gypsum externat renders of Paris: history and fabrication

1850

[ 171 Ferroussat de Castel bon, f.11., Réflexions sur la mauvaise qualité du plâlre et sur sa cause, Paris, Lottin Ainé, 1776

[ 181 Nadaud, M., Mémoires de Léonard, ancien garçon maçon, Paris, 1895

1191 de Lespinasse, R., et Bonnardot, F., 1879 -Les Métiers et corporations de la ville de Paris -XIIIe siècle, le livre des métiers d'Etienne Boileau; l listoirc générale de Paris, Imprimerie Nationale

1201 Trcatiscs used to establish the traditional application of gypsum cxternal rcndcrings:

dc'Aviler, A.G., Cours d'Architecture, (Paris: N. Langlois) 1691

Bullet, P., Architecture Pratique, (Paris: J.13 Dclespinc, J-T l lcrissant) 1741

Diderot, D., et D'Alembert, J le R., Encyclopédie ou Dictionnaire raisonné des Sciences. des Arts et des Métiers, par une société de Gens de lettres, Original cdition onlinc: http://portail.atill'.fr/cncyclopcdic/, 1765 Patte, P., Mémoires sur les o~jels les plus imporlans de l'architecture, (Paris:

Rozet), 1769

Lucotte,J, R., L'Art de la maçonnerie, (PariT: Imprimerie de Moutard), 1783 Rondelet, J,P., Traité théorique et pratique de l'art de bâtir, (Paris: Privatc), 1827 Siston, V., Manuel théorique et pratique du Chaufournier., (Paris: Manuel Rorct), 1836

Claudel, J., et Laroque, L., Pratique de /'Art de Construire en Maçonnerie, (Paris: Carilian-Goeury et V.

Dalmont), 1850

Toussaint, M., et Magnier, M.D., Nouveau Manuel Complet du Maçon, du couvreur, du paveur. (Paris:

Manuel Roret), 1864

Chabat, P., Dictionnaire des termes employés dans la construction, (Paris: Morel), 1876 Oslet, G., Cours de Construction, Matériaux de Construction et leur emploi, (Paris), 1885

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