Red Earth_David Gissen

Fazemos agora a ligação a uma interessante reflexão teórica de David Gissen, arquitecto, historiador e crítico de Arquitectura, no seu blog www.htcexperiments.org sobre diferentes perspectivas conceptuais de utilização contemporânea da terra.
Cruzando exemplos do recente livro Earth Architecture de Ron Rael com projectos experimentais, Gissen desenha uma ideia da terra afastada do senso comum, um conceito de material vivo, com alma, ao mesmo tempo forte, histórico, pobre, frágil, imaterial, associado à morte e à vida.

"
I always enjoy talking to my friend and colleague Ron Rael. Ron is the author of Earth Architecture, an excellent book that outlines the history and explores in-depth contemporary uses of earth in architecture.

Ron’s book is a book about design, but it’s also a powerful corrective to those commentators that view buildings made of earth, or the matter that constitutes earth buildings (mud, sand, gravel, soils), as primitive, poor, or crude. One of Ron’s points is that earth buildings have a far more complex history; describing earth matter as inherently “poor” is often just a way to tie specific practices to specific (often global southern) geographies and histories. As Ron notes, earth is free; but this does not suggest that it is a defacto representation of poverty. In more recent discussions, Ron describes earth as a type of infrastructure. In his narrative and case studies earth emerges as a material with far reaching technologies and representational implications.

Ron’s book is engaged with aesthetics, technology, and history; it’s less explicitly concerned with political problems. But in releasing earth’s denigrating associations with poverty, we are left with more than just “rich” earth; we arrive at a less denigrating poverty of earth that is tied more to the “common” than the geographically poor. When I consider free earth molded into something more than a representation of the poverty of those building with it, I begin to imagine it also being part of a terrapolitical structure — a “red earth.” This earth that may be at some base level “poor” but also open to a new image, much more than “not poor”.

In arguing for a red earth, I’m not arguing that earth holds an innate leftist proletarian politics in its chemical composition, nor am I completely arguing for the social construction of earth. I am arguing that our engagement with earth offers the possibilities for new liberatory ways of understanding space, that remain tied to earth’s commonness.

A powerful concept of red earth, tied to its ubiquity and free nature, might be found in the roots of much red thought — Marx himself. In his Critique of German Ideology, Marx understood earth (as concept and thing) as the base of political economic philosophy. In one of his most famous passages, he wrote “In total contrast to German [idealist] philosophy, which descends from heaven to earth, we here ascend from earth to heaven.” Marx saw earth (both soil and “the earth”) as the base of his philosophy because it was the defacto element that contained the material and ideological possibilities of society (its nourishment, production, and metaphysics). For Marx, earth contains the conditions of society by society. Earth not only delivers the grains grown by a farmer, but when a person digs his shovel into earth to grow something he or she becomes “a farmer.” When a person binds the earth into bricks he or she becomes “a builder.” The earth is social matter and structure, how we engage with it repeats existing structures and opens up new concepts.

Red earth also becomes red through its potential to release the history of the common, the poor, the defeated. Earth is an endless historical archive of tragedy that does not have to be nurtured, funded, or maintained (like most archives) to hold records of such tragedy. As an archive of social misfortune, our engagement with earth is a barometer of how we come to grips with our crimes. Murder, corruption, and lurking forms of power are hidden through manipulations of earth (from mass graves to buried toxic pits). But these things often reappear through manipulations of the earth.

What is the fascism and corruption that appears in contemporary film but a big earth-burying operation? The justice that often appears in film is a big excavation. Consider some of John Sayles recent films in which the bad guys bury their crimes and the good guys, quite literally, go into the earth to excavate those crimes. Or just about any film that explores genocide involves mass burials and excavations.

This more red earth, that is the condition of society and the history of society, appears in a few contemporary works of architecture. One of my favorite “earth” projects, The Irish National Pavilion is discussed by Ron in his book; it’s a project about history, denigration, and earth. Another more explicitly red project (not in Ron’s book) is the Open Air Cafe proposal by Manuel Herz, which I wrote about in my article “Debris” in the current issue of AA files (and that also appears in Subnature (along with the Irish Pavilion)).

In this latter project (see image here), Herz proposes excavating the ground of Cologne — site of one of the most notorious bombings during World War II — and heaping the mixture of earth and war debris (held within the earth of Cologne) over a series of concrete armatures for a park cafe. The war debris becomes a type of historical material that forces residents of Cologne to consider the history within earth and the conditions of a future nature in this particular city. It’s a proposal that enables us to see earth, the crimes it holds, and its potential representational structure in historical terms.

This brief discussion of a red earth builds on Ron’s observations. I think it also positions some ideas about earth differently from those concepts of earth and ground in either contemporary green or parametric design. Both of these latter movements see earth as an uncorrupted source of vitalism for a future architecture; an instrument of literal or digital vectors springing out of its surfaces. The earth of Herz (or the Irish Pavilion) is an earth examined (versus generalized); it’s an earth that is historical without being historicist; and it offers us images of earth as both life and violence against life, versus a more flippant vision of life and beauty."

By David Gissen in Red Earth June 5, 2009

Apresentação_Hubert Guillaud_Tierra2001

Construção em Terra no Vale das Rosas, em Marrocos (c) Xavier Fabre

Postamos aqui um excerto introdutório da apresentação pelo Professor-Arquitecto Hubert Guillaud, Director científico do CRATerre-EAG, no Congresso TIERRA: CONSTRUCCIÓN, RESTAURACIÓN em Valladolid, Espanha, em Maio de 2001 .

A apresentação está em Espanhol e o tema é « La conservación y el restauro de las arquitecturas de tapial : métodos, diagnostico y tipologia de las intervenciones ». Divulgamo-la pela sua clareza e para introduzir a temática da Recuperação de Estruturas em Terra de que falaremos nos próximos posts.

"La cuestion crucial del mantenimiento y de la conservación de las culturas constructivas y arquitecturas de tierra

En todo el mundo existe un riquísimo y vasto tanto como mucho diverso patrimonio arqueológico-arquitectónico construido con tierra.

Tal situación suggiere un enorme esfuerzo en la conservación, restauración o rehabilitación de esta herencia excepcional. Podemos considerar la dimensión de la tarefa, verdaderamente colosal, si tomamos en conto todas las declinaciones del uso de la tierra en construcción y la tipología arquitectonica mucha ámplia cubriendo ciudades históricas enteras, sitios monumentales, arquitectura vernácula en regiones rurales, paisajes culturales, superficies decoradas, así como la variedad de las culturas constructivas y la complejidad de los sistemas constructivos.

Si la tierra es utilizada por milenios desde la antiguëdad en muchas regiones del mundo, uso universal que llegó a traves de los tiempos hasta hoy, si sabemos que muchas partes del mundo pueden siempre manifestar practicas vivas de construcción con tierra, sabemos también que la mayor parte del saber hacer en las prácticas de mantenimiento o de construcción ha desaparecido, particularmente en regiones desarrolladas que han quasi totalmente eradicado estas culturas milenarias.

Sin embargo, la importancia del patrimonio arquitectónico de tierra, su valor cultural y social como su valor económica vinculada a un mercado real o potencial de conservación, restauración o rehabilitación exige competencias profesionales para actuar. Porque lo que vemos considerando las practicas de conservación, en su mayoría, es dramático. De facto, muchas veces, las intervenciones no tienen conto de los carácteres específicos del material tierra, de los sistemas constructivos y del diseño arquitectónico próprio.

Excepcionalmente, cuando se actua sobre un patrimonio histórico, las practicas estan mejores por tanto que existe la competencia. Pero esto tipo de situación privilegiada es muy rara y constatamos una falta dramática de estas competencias que sea en el dominio profesional de la conservación arquitectónica como en el sectore de la construcción actual. Lo que vemos es restauración muy féa con el uso del hormigón armado o con bloques de hormigón, con repellos de cemento, con una carencia dramática en la realización previa de un diagnóstico analizando las patologías e integrando no unicamente los aspectos y criterios técnicos pero también los factores de los entornos físicos, climáticos, sociales y culturales que son también en la origen de problemas y degradaciones mayores.

Conjunto de edifícios em "pisé" (taipa), Saint Trivier, Moignans, em França

Así para hoy y para el futuro, la regeneración del saber hacer y de la competencia profesional es un reto crucial. Tan crucial que el interés por el estudio y la conservación de las arquitecturas de tierra, también si es creciendo, esta siempre reciente. No existe una amplia « toma de conciencia » de la parte de la comunidad profesional dedicada a la conservación o a la construcción. Esto interes se ubica en medios sensibilizados que son privilegiados, más a nivel científico o académico que a nivel profesional.

El reto de la actualización de las culturas constructivas de la tierra, para la conservación como para la construcción nueva es claramente vinculado al desarrollo más amplío del campo de estudio de las arquitectura de tierra, al reconocimiento de esto campo como una disciplina o como una ciencia y necesita el desarrollo de programas integrados de formación académicas, de capacitación profesional, de investigación, de aplicación en muchos más proyectos demostrativos y de difusión de los conocimientos científicos como técnicos relacionada a una dynamización de la concientización.

Esto reto es también mucho importante a nivel cultural si consideramos la pertinencia de un desarrollo sostenible que debe favorecer el transfero transgeneracional de la biodiversidad y de la tecnodiversidad para contraponerse a los devastadores efectos, ya patentes, de la transculturación en materia de arquitectura y en otros dominios en muchas regiones del mundo donde existe una herencia de excelencia de la arquitectura de tierra expuesta a un riesgo de desaparición rapida si no actuamos para crear y consolidar las condiciones culturales y sociales, técnicas, económicas y legales, también políticas adecuadas.

En favor de estas perspectivas podemos considerar que quizás, la conservación del patrimonio construido con tierra tendrá inevitablemente que pasar por la promoción del « nuevo ». Pero solamente una modernidad basada en el profundo conocimiento y consideración de la historia, así como de las tradiciones especificas y de los saber hacer locales parece ser factible y viable. (...)"

Água e Argila_Construção com Terra

A água _Principal ligante da terra

O elemento H2O água tem um papel essencial na aptidão da terra como material de construção. É ela que reforça a sua coesão e aumenta decisivamente a interacção entre as partículas de argila.
Na verdade, uma parede em terra nunca está completamente seca, e ainda bem, ao contrário do que se possa pensar. Ela contém sempre água entre as argilas.
Uma água que não se evapora, uma vez que se encontra em equilíbrio com a humidade relativa do ar envolvente. Neste estado de equilíbrio hídrico, a terra contém no seu interior cerca de 2 a 3 % de humidade (variável). Isto é equivalente a aprox. 16 litros de água para uma parede de 3 metros e 50 cm de espessura. Sem esta água seria impossível construir a parede em terra, esta desagregar-se-ia, devendo-lhe por isso grande parte da sua coesão e a sua forma de sólido coerente e estável.
Neste sentido, os testes de teor de água na terra para taipa são interessantes porque mostram que as suas propriedades variam significativamente com as variações na percentagem de água. Ao examinar os diferentes estados da terra, da sua transição de seco para molhado, percebemos, por exemplo, que um ligeiro aumento na quantidade de água induz rapidamente a transição do estado plástico para o líquido.
Por outro lado, algumas regras de composição granular podem também ter impacto na coesão da terra. Se, ao adicionarmos água, também incluirmos elementos como areia ou cascalho, esta estabilização permite controlar a fissuração do material.

Foto de Caulinite realizada com microscópio de scan electrónico.

Neste sentido é importante perceber a Argila e a sua relação com a água.
Os Grãos de argila, pela sua pequena dimensão e forma, estão sujeitos a forças capilares muito mais elevadas do que os outros grãos, maiores e arredondados.
Estes diferem dos outros componentes da terra, não só em tamanho, mas também pelas formas microscópicas lamenlares que lhes dão uma massa insignificante comparada com a sua superfície. Nestas micro-lamelas, as propriedades superficiais são determinantes, e na presença da água, as suas propriedades macroscópicas, como a plasticidade e a coesão ganham presença.

Esquema da ligação da argila e água entre grãos de areia

Depois a compressão da terra faz o resto.

A resistência da terra está directamente relacionada com seu grau de compactação quando é comprimida por um determinado esforço. Para cada tipo de solo e para cada esforço de compactação existe uma determinada humidade, denominada humidade óptima de compactação, na qual ocorrem as condições em que se pode obter a melhor compactação, ou seja, a maior massa específica seca.

Nestas condições, o solo apresenta também menor porosidade, caracterizando-se assim num material com maior durabilidade e maior resistência mecânica.

A humidade óptima de compactação pode ser determinada em laboratório através da medição da massa específica do solo sujeito a diferentes humidades, compactado num determinado molde (cilindro de Proctor).

As massas específicas são representadas em gráfico, em função da humidade, e a sua massa específica máxima, obtida na curva, define a humidade óptima de compactação do solo específico (ver gráfico).

Selecção de Solos e Métodos de Controle em Construção com Terra - Práticas de Campo_Proterra

Por tudo isto, dizem os conhecedores, e com razão, que na construção em taipa estamos a fazer pedra num curto espaço de tempo, aquilo que a Natureza leva séculos a criar.

Blog_Perspectiva de Futuro

Parede em taipa, Zambujeira do Mar, Odemira.

Somos verdadeiramente apaixonados pela construção em terra.

Fazemos parte orgulhosa daquele grupo dos que se emocionam com a simplicidade e coerência incrível destas técnicas, com a beleza das cores e texturas, com a subtileza e importância dos detalhes, com a riqueza construtiva e cultural da terra.

Somos dos que entendem e defendem o material terra como uma escola de sustentabilidade, só possível através da humildade e da experiência. Sabemos que fazemos parte deste Futuro e já imaginamos como serão a formação, o projecto e a construção em Terra daqui a 10, 15, 20 anos.
Na semana passada fomos desafiados, e ainda bem, a observar e relançar o trabalho desenvolvido no Blog do ponto onde nos encontramos, quais os nossos sonhos, o seu potencial e que caminho queremos seguir.

Aceitámos o convite, dialogámos com quem sabe mais, aprendemos conversando e fizemos novos amigos.

No Blog somos visitados diariamente por dezenas de curiosos e entendidos na matéria, recebendo feedback dos vários cantos do Mundo.
Acreditamos estar a construir com o ArquitecturasdeTerra um espaço aberto e responsável, centrado na universalidade da construção em terra, de divulgação, conhecimento e discussão de ideias.

Neste sentido, e de forma a ampliar esta plataforma de sinergias relacionadas com a terra, estamos apostados em promover uma MOSTRA DE PROJECTOS ON-LINE com posteriores visitas às obras de terra, dialogando com os projectistas e construtores, organizando DEBATES e mesas redondas, ENCONTROS e EXPOSIÇÕES sobre a terra.

Queremos debater tudo, desde as razões Históricas, sociais e culturais, aos aspectos técnicos, físicos,químicos e até estéticos da construção com terra.

Convidamos por isso todos os interessados que tenham projectos e/ou obras construídas, ideias para debate e divulgação, a contactarem connosco para o mail: arquitecturasdeterraatgmail.com, ou pelo tlm 914854458.

Os sonhos para o Futuro da Arquitectura de Terra constroem-se hoje.

Texto_Building with mud, glorious mud_BD

Building with mud, glorious mud

06 February 2009

An email arrives from Jean Dethier, director of the Pompidou's architecture exhibitions between 1975 and 2004. Remember Le Temps des Gares, Images & Imaginaires d'Architecture, Architecture de Terre? Great exhibitions, all. Dethier wants to tell me about a lecture he's giving, "Building with Raw Earth: an eco-revolution?" on February 17 at Fitzwilliam College, Cambridge.

This was a timely message as when it came, I was sorting through photographs I'd taken as a student of a trip through Saharan Africa to Djenne and yes, to Timbuktu, when getting to either town was an adventure even by sturdy Peugeot 404 pick-up.

Last year, I heard a Cambridge student confidently telling her colleagues, "everyone has been to Djenne." Perhaps they have. Magazines, TV documentaries and the internet have made the mud mosque at Djenne as familiar as Notre Dame, and I imagine there must be an Easy Jet or Ryanair flight to Mali for the price of a handful of dust.

What thrilled me at Djenne was the fact that such an ambitious building could be made of mud. Proper religious buildings, indeed all proper buildings, were surely made of brick, stone and timber, or concrete, steel and glass?

When I returned from Mali, I happened to stay with friends at Collompton in Devon, and their venerable cottage proved to be made of... mud. Well, of cob to be exact. This got me excited. I began investigating mud or "raw earth buildings", delving into the history of vernacular structures and how their construction had formed a variety of different styles as rich as it was delightful, a variety nurturing a true sense of place in the days before comprehensive redevelopment and urban regeneration, along with a nationwide developer housing spree, had made everywhere begin to look much of a much.

What I also learned was that modern forms of construction, married to rules, regulations and general bullying by governments and officialdom, meant that houses were built to increasingly similar specifications. Even if a new house tried to blend in with its old neighbours, it stood out because of its scale, proportions, the size of its windows and so on. The art of building with local materials gave us houses with a delightful range of styles, proportions, thicknesses of walls, depths of window reveals, shapes of roof... the list goes on. If we could find economical ways of building modern houses from local materials, we might yet escape the banality of 90% of contemporary housing design, buildings raced up without love and with little respect for locale.

Imagine if British housebuilders were asked to extend Djenne or Timbuktu: these towns would look like the fringes of Doncaster or Telford. It would be good to see some of Britain's most inventive architects learning to wallow in mud. Jean Dethier is offering to show them how.

From BD (Building Design Magazine)

http://www.bdonline.co.uk/

Standard Code of Practice for Rammed Earth Structures_Zimbabwe

'The Zimbabwe Standard Code of Practice for Rammed Earth Structures’

Texto_Technology for architects keen on low-energy design

Aqui fica um texto em inglês sobre a realidade da construção em Taipa no Reino Unido, mas que diz muito da técnica e do futuro das construções sustentáveis.

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Technology for architects keen on low-energy design

Rammed earth is going mainstream as a result of its insulation and sustainability
properties.

There's no shortage of smart technology for architects keen on low-energy design. Glasscovered
Trombe walls, brises soleils and innumerable permutations of highly insulated curtain wall are today's mainstream technology. But how much of this innovation is just a solution looking for a problem? Are complex multi-layered building envelopes really more effective at temperature and energy control than a basic mud hut?

Proponents of rammed wall construction would argue the toss. They would point out that earth is free, earth is plentiful, and when compressed it has excellent thermal and acoustic insulation properties. All one has to do is excavate the soil, add a chemical stabiliser such as lime or sugar paste, compact the earth between wooden formers, and hey presto, you have a durable, strong and highly insulated wall.

The build process is simplicity itself. The selected soil is mixed to the right consistency, then compacted in layers using hand tools. Formers are used to act as a mould for thewall. Other materials can be added to improve compaction, such as ground glass, shredded rubber tyres or natural fibres. Once the wall has been constructed, the formers can be removed. The wall is immediately ready to take structural loads. Rammed earth walls used as internal partitioning can also suppress noise transfer between rooms very effectively. At the Eden Centre in Cornwall, the walls of the visitors' centre were built from earth excavated on site. The soil was compacted by hand to form 40 panels, each 2.5m high and weighing around 10 tonnes. The walls were strong enough to support themselves without reinforcement on the day they were built, and to support the roof loads of the centre. But while it's not surprising to find rammed earth walls at beacons of sustainability such as the Eden Project, the technology is also turning mainstream. Newcastle based architect Jane Darbyshire & David Kendall (JDDK) has designed Europe's largest internal rammed earth wall for the Rivergreen Business Centre at Aykley Heads in Durham.

Interestingly, the decision to create a rammed earth wall in the Aykley Heads project was driven by the client, Rivergreen Developments. The company had seen an earth wall at the Autonomous Environmental Information Centre (AtEIC) project at the Centre for Alternative Technology in Powys, and was keen to try the technique as part of its commitment to sustainable construction.
"We visited the AtEIC project with the client and were very impressed with the thermal and aesthetic qualities of the rammed earth wall," said JDDK's project architect Ruth Walters. "Although we didn't have any experience with the technology, the client was willing to take the risk. We also worked with consultants experienced in designing and building rammed earth walls."

The 6m-high, 600mm-thick rammed earth wall brings environmental benefits, because it uses natural materials readily available on site; and performance benefits because it offers a relatively cheap and simple method of creating a high thermal mass within the building to even out swings in temperature. It is also believed to help control moisture in the building.

The wall has been constructed in six separate panels inside the atrium of the 3,700sq m, two-storey, timber-framed building. Being south-facing and subject to direct solar gain, the wall absorbs the sun's energy during the day and releases it at night and early morning to preheat the adjacent offices prior to occupation.

The rammed earth wall is the most innovative of the building's sustainable features, which include space heating provided by a biomass boiler fed with wood pellets, and collecting rainwater for toilet flushing and irrigating the building's sedum roof. These helped it achieve an "excellent" Breeam rating. Approximately 80% of the material used in the wall's construction is fine sand obtained from the basement excavation. The remainder consists of gravels and clay from local quarries. The success of the method depends upon the proportions of the mix and the
overall moisture content, which will be unique to every wall.

Since there is no firing process and no toxic emissions, the amount of CO2 emitted depends solely on the transport requirements for additional materials, such as clay and chemical stabilisers. The Aykley Heads wall used 60% site material, with the remaining 40% transported in.

For the project, JDDK commissioned Bath University's Department of Architecture & Civil Engineering to develop the optimum blend of clay, sand and gravel and advise on improvements to the soil to improve compaction and cohesion. The team constructed sample panels to check stress resistance. JDDK's Walters feels this was a crucial step. "We would stress the importance of getting sample panels made and testing them for their aesthetics as well as their durability," she says.

Following its success at the Aykley Heads centre, JDDK Architects has since specified an external rammed earth wall for the £4.1 million Wild Bird Discovery Centre on Teesside. "The main risk is to do with controlling the shrinkage of the wall," says Walters. "At Aykley Heads we were able to build in a controlled environment - it's much easier to build internally. But we still made the wall in six separate panels, with expansion joints between them."

Other downsides of rammed earth construction include a lack of national guidelines for design and construction, higher labour costs for the compacting process, and limited data on the materials' physical characteristics. There is no shortage of guidelines for hot countries such as Australia, but very few in the UK.

The most recent guidance is a BRE book Rammed Earth: Design and Construction Guidelines published last year. It gives practical advice on the material selection, construction, design, detailing, maintenance and repair of rammed earth walls. JDDK relied heavily on Simmonds Mills, a Hereford-based firm which acted as the rammed earth consultant for the AtEIC project and led the team that constructed the walls. At Aykley Heads, it advised JDDK on soil types, shuttering and construction methods, and trained the construction operatives in earth-ramming techniques.
In common with many construction materials, the thermal performance of a rammed earth wall depends on its density, porosity and water content. Rammed earth walls between 1,400 and 1,800 kg/cu m can have thermal conductivity U-values of 0·7 to 0·9W/sqmK. As a comparison, the CIBSE Guide quotes thermal conductivity of 0·51W/sqmK at 1,400 kg and 0·87W/sqmK at 1,800 kg for homogenous masonry.
Allowing for normal internal and external surface resistances, and assuming the wall will be rendered and plastered, a nominal wall thickness of 2m may be needed to achieve a Uvalue of 0·35W/sqmK. Additional insulation is likely to be needed where rammed earth walls are used externally. Insulation would be best placed on the external elevation, leaving the internal spaces to take advantage of the wall's thermal mass.

Essentially, any finish that can be applied to brick or concrete can be applied to a rammed earth wall, such as tiling, rendering, lime washes, pebbly finishes or a clear coating of silicon emulsion to seal the earth. Environmentally friendly surface treatments include boiled vegetable extracts.
Undoubtedly rammed walls are a worthy contribution to sustainable architecture, but their use will not outweigh the energy used by conventional gas-fired heating or electrically powered ventilation. Architects seeking to reduce carbon dioxide emissions need to approach rammed earth walls as part of a wider strategy to reduce CO2 emissions. One thing they must not become is lipstick on the gorilla.

From http://www.simmondsmills.com/

Date: 13/05/2006

"

Norma UNE 41410:2008_Espanha

Esta notícia é fresquinha e já está disponível, uma nova norma sobre construção com terra em Espanha.

A norma é a UNE 41410:2008
“Bloques de tierra comprimida para muros y tabiques. Definiciones, especificaciones y métodos de ensayo”

Esta é a primeira normativa espanhola não experimental de um Organismo de Regulamentação Europeia.
Após alguns anos de trabalho, o subcomité AEN/CTN 41 SC 10, da Asociación Española de Normalización (AENOR), entidade de regulamentação espanhol, responsável pela elaboração das normas espanholas (Normas UNE), semelhante a outros organismos europeus DIN (alemão) e o AFNOR (francês), elaborou e aprovou a Norma UNE 41410.

Ela foi criada, segundo a AENOR, pela necessidade de caracterizar o material, descrevê-lo e conhecer as propriedades da matéria-prima e os produtos associados, assim como os testes e ensaios necessários.

Um agradecimento especial a Ignacio Cañas pela informação e um recado aos legisladores Portugueses, num país que legisla tanto e sempre a reboque dos demais, está na hora de olhar para a construção com terra com o reconhecimento e a importância que ela merece.

Artigo_Materials World_Feat of Clay_Tom Morton

Postamos agora um interessante artigo de pesquisa de Tom Morton, Arquitecto da Arc Architects, da Escócia, UK, publicado na Materials World em Janeiro de 2006.

FEAT OF CLAY
Moves to develop UK production of unfired clay bricks are driven by the growing demand for sustainable construction materials to displace conventional products. Tom Morton, Principal Architect at Arc, Fife, UK, examines the key factors in achieving a scale of use that would yield significant benefits, such as standardisation and low cost.

The main advantages of using unfired clay as a binder in building materials instead of cement, gypsum or fired clay are a healthy indoor environment and low environmental impact over the whole life cycle of the material.
These attributes have been well established over the last fifteen years in Germany, where a small specialist construction sector has experienced sustained growth through the development of national standards in using unfired clay and the use of sophisticated products in prestige projects.
But application in the UK has been hampered by the lack of guidance and standardisation in available materials and the expense of importing modern products from Germany. The development of best practice guidance and low cost materials manufacturing in the UK would remove significant barriers. Attention now focuses on ways to realise this shift in attitude.

In order to assess the potential of unfired clay bricks in the UK, a test house was built and monitored in a research project funded by the DTI Partners In Innovation programme. This two-year project reveals the technical advantages of using unfired clay materials and highlights practical implications of their use.
Low impact manufacturing Unfired clays are natural materials with varying properties, commonly combined with fine aggregates and fibres to make a range of products such as bricks, blocks, boards, mortars and plasters. Clay materials produce very little waste, as there is no fundamental chemical change or ceramicisation involved in their manufacture and use. The materials are easily recycled or cleanly disposed of.

Although clay manufacture uses a finite resource, the environmental impact can be benign, with low value agricultural land being transformed into biodiverse wetland habitats.
Sources of clay are shallower and less remotely located than sources of gypsum and cement or lime.
Unfired clay materials also have relatively low embodied energy and carbon. The brickwork in the test house had embodied energy of 146 kwh/tonne and embodied carbon of 44.6 kgCO2/tonne. This is about 14% of comparable fired brickwork and 24% compared to light-weight blockwork. While the bricks were removed from production before kiln firing, they still required two days of artificial air drying.
The estimated saving in this building is 24.9MWh and 7036kg of CO2 over common bricks, and 14.5MWh and 4104kg CO2 over light-weight concrete blocks.

Healthy living
An ability to regulate moisture is another key quality of unfired clay materials. Their hygroscopic scope to absorb and desorb atmospheric moisture allowed the 15mm clay plaster surface in the house to strongly regulate short-term peaks. In the bathroom, the clay plaster had such a strong ability to absorb peaks of air moisture after showers that it cleared the air without surface condensation. The effect of the extractor fan was of no statistical significance.
The brick core had a longer term moderating effect, peaking at two hours after exposure to moisture, but continuing for over 24 hours.
The ability of a building’s fabric to passively avoid conditions where condensation will occur improves its long-term durability and avoids the need for vapour control membranes, which are prone to defects from poor workmanship.
However, the main advantages in moisture terms are to human health through the regulation of internal air relative humidity (RH).

The UK has some of the highest rates of asthma in the world and allergens from house dust mites are known to cause asthmatic sensitisation and trigger symptoms. Recent research recommends maintaining internal RH below 60% to ensure that the dust mites critical equilibrium humidity will not be reached.

Designing dwellings with a high level of insulated thermal mass can help to achieve this. Allergy to mould spores is a major health risk associated with fungi in buildings, and the inhalation of mould spores can also cause toxic reactions and cancer. Relative humidity levels below 70% are thought to avoid mould growth.

Avoidance of high RH levels can also reduce the viability of bacterial disease transmission. Although low relative humidity can cause respiratory disease through the drying of the throat, the risk is considered less than that presented by dust mites and mould at high humidity levels.

When monitoring the test house, the target of regulating levels to between 40% and 60% was generally met. While there were short-term values outside this range, these were attributable to periods of very high ventilation or the use of showers. While external air relative humidity fluctuated considerably, between 24.9% and 96.1%, the mean external value was around 65%, while the mean internal value was around 45% (see graph).

All images ©Arc

Comfort levels
Used on the inside of a layered construction, the unfired clay bricks made a significant contribution to thermal comfort, with warm surfaces and thermal mass that moderated atmospheric temperature swings for up to a week. Effective U-value (the rate of heat loss) of the walls was 32% better than the design calculation, though the reason for this was unclear. The improvement may relate to optimisation of the density of the cellulose insulation or a better than predicted performance by the earth brick and plaster related to air in the earth pore structure.

Occupants of earth buildings often report better perceived thermal performance than is predicted by steady state U-value calculations, which can prove inaccurate predictors of real building performance for a number of reasons.
Whatever the explanation, the walls of the building performed significantly better than was indicated by the design calculations and exceeded the requirements of the contemporary building regulations.

Down to earth
The future for earth construction in the UK remains uncertain. Unfired clay's fundamental properties as a flexible, healthy, low-energy binder give it great potential in an evolving sustainable construction industry. Earth masonry construction is simple and cheap, and could help establish a basic mass-market for earth materials in the mainstream sector, fostering more exciting research and development into prefabricated composite materials and spray applications.
But the commercial reality is that while some major brick producers are developing unfired products, the kind of investment that is needed for a progressive leap is still some way off.

Further information
Arc Architects led this research in association with Dundee University, UK, and Robert Gordon University, UK.

Tom Morton is the Principal Architect at Arc Architects, 69 Burnside, Auchtermuchty, Fife KY14 7AJ, Scotland. Tel/fax: 01337 828644

Email: tom@arc-architects.com

Rammed Earth_With a veneer of science_David Oliver

Rammed Earth - with a veneer of science

David Oliver, an australian architect from Queensland has spent a significant part of his professional life applying science to the simplicity of rammed earth construction. He is now recognised as a world leader in rammed earth technology and a significant driving force behind environmentally sustainable design in Australia. Along the way, David, who is based at Mooloolaba, on Queensland's Sunshine coast, has lifted the standing of the still-simple rammed earth technique to the same level as other 'conventional' construction methods.
David is the principal of his own architectural firm and its companion consultancy which is the vehicle for his pioneering technical work in rammed earth construction. He believes rammed earth will become ever more widely accepted and used over the next decade as more people become aware of it, and as the relative cost of other building materials increases - something he believes is inevitable.

"I believe rammed earth construction will become accepted as standard throughout Australia, with sub-contractors and builders who will specialise in the technique."

"There are already more than a dozen contractors around Australia specialising in rammed earth construction."

"Rammed earth has significant environmental and aesthetic appeal, and construction costs are comparable to the cost of building in cavity brick. It also has very good thermal modulation and acoustic insulation properties."

"The aesthetic appeal is very strong because rammed earth construction reflects, without interpretation, the natural colours of the locality."

"The colours of rammed earth buildings vary from district to district, depending on the colours of the materials available in the local area."

"Perhaps the strongest environmental benefit from rammed earth construction is that there is no firing involved, as there is with brick and cement, so the product is very low in embodied energy.

"I expect the cost-balance to change to significantly favour rammed earth construction over the next ten years, as the cost of energy increases and carbon and energy taxes are imposed."
Rammed earth was relatively labour intensive - about 60 percent of the cost of rammed earth construction is labour, David said. A wall can be constructed at about the rate a tradesperson could lay a brick wall.
David attributes his initial interest in earth construction techniques to 'romanticism'. "I was of the 60's generation, which was strong on idealism, and as an architect imbued with a good measure of idealism, earth construction appealed.

"My interest developed long ago before 'sustainability' became an issue."
When he started investigating the potential of earth construction, it soon became apparent that, largely because of the labour requirement of many forms of earth construction, rammed earth was the only commercial option in the Australian context, and since the 1980s, David and his associates have concentrated on rammed earth techniques.

"Initially I started designing for rammed earth construction and trying to get other people to construct the buildings, but that proved very difficult so we decided to learn how to do it ourselves. That also proved difficult. We found there was a global lack of knowledge about what made one building successful - that is, structurally sound - and another not. We could identify the problems but no-one seemed to know the answers."
In 1985, David travelled through the western provinces of China to learn more about the traditional earth construction methods used there and the following year he gained a Churchill Fellowship which enabled him to visit France, Germany, Britain and south-west USA to learn first-hand about the earth building techniques used in those countries.

"Some of the rammed earth buildings I saw in France were stately homes and mansions which have stood for more than 300 years. Rammed earth was used in France in the mid 17th century where suitable raw material was available and many of those buildings are still in use and still recognised as outstanding examples of the architecture of the period. On that study tour, I found that Australians knew as much as there was known about what was involved in successful rammed earth construction. We were then, and still are, at the cutting edge of modern earth building".
David's focus on rammed earth led eventually to technical definitions of the 'mix' of ingredients necessary for reliable construction; a development which he sees as the key to the potential of rammed earth as a modern construction material. "We set out to work out why some mixes worked and others didn't, and the end result is a physical and chemical definition of the necessary mix characteristics based on standard engineering analyses".
He is also involved in the final stages of trialling additives which will stabilise clays -an essential ingredient of the rammed earth 'mix' - and so prevent degradation of rammed earth construction by water. "Too much water can, in some instances, destabilise the clay particles and break down the mechanical bond formed between the particles. We have identified and patented additives which prevent that."
David believes identification of the additives, and definition of the physical and chemical characteristics of the construction mix, are the two biggest steps forward in the technical development of modern rammed earth construction: "We have taken the guess work out of the process. We are still using the traditional methods - compacting earthen material between forms which determine the shape of the construction - but in the past, determining the material to be used was a matter of trial and error or traditional experience. We realised very early on that to work in the modern context, with formal engineering and structural specifications to meet, we needed to be absolutely certain that we could produce consistent, high-quality results every time, building after building, no matter where they were located.
"If rammed earth was to be accepted as a modern building technology, it needed to be applicable to all areas and had to be able to be analysed and understood so engineering tests could be undertaken. At the same time, we wanted to use local material. Knowledge of the essential physical and chemical characteristics of successful rammed earth mixes enables us to develop a technical description of the ideal mix, and we are able to blend local materials to produce mixes with those characteristics."

Access to that information was now available through David's consultancy service for architects, engineers and builders interested in working in rammed earth, David said.
"Using our knowledge of the characteristics required, we are able to combine local materials, usually from several quarries, to achieve a mix with the necessary physical and chemical properties.
The materials included in a mix, and the proportions to be used, were determined on the basis of standard engineering tests of physical and chemical characteristics, said David. "Once we have worked out the mix, construction is a simple matter of dampening and compaction, as has been done for centuries, although we use modern technology for the compaction and do use one or two additives. We add a very small proportion of cement - about five percent by weight - to maximise erosion resistance, and the new additive to prevent bio-degradation as a result of excess moisture will become a standard part of the mix."

"The mix consultancy is done long-distance, in much the same way as a soil test. The builder or the consultant identifies a source of material he or she thinks might be suitable and sends our company a sample. We do an analysis and if something is lacking, we tell them what else to look for. Alternatively, they might send us several potential ingredients and we analyse the raw materials and develop the mix that way. Once we have all the components, we calculate the proportions and after that it is up to them."

"The construction technique is very simple. The key to success, and the soundness of the building, lies in the mix used."
With the technical side under control, David and his associates set out to promote awareness and appreciation of rammed earth construction through its use in prestige buildings. "We formed a construction company specialising in rammed earth techniques and set about winning a major project to boost its profile. We needed to show that rammed earth was good structurally and, from a design perspective, complied with current design and technical requirements, and was cost effective. We reasoned that a major project would increase public awareness of rammed earth and we would see a 'trickle-down' effect, which has happened.
"We needed to convince people we could build practical, commercial structures."

David Oliver is head of Greenway Architects and CEAC building consultancy. For contact details, see the Alternative Directory under Architects or Earth Builders or Ethical Building/Design Advisory Groups.

All Photos were taken from http://www.stabilisedearth.com.au/index.html website, an australian rammed earth building company created in 1986 by Ian and Tina Collect.

Natural Building Materials_Matt Muldoon

Natural Building Materials
by Matt Muldoon

By natural building materials, we mean building materials which require no or relatively small amounts of processing, and which will return to the earth without causing undue pollution. Common natural building materials are earth, straw, wood, stone, lime and hemp.
Common to all natural building materials is their low embodied energy. Embodied energy refers to the energy consumed over the lifetime of a building material, in its manufacture, processing, transportation, application and demolition. Bricks, for example, consume a huge amount of energy in that the raw materials are mined, processed, fired in a kiln, transported large distances, applied with the help of powered machinery and demolished and disposed of with more powered machinery. A contrast would be straw bales, which require relatively small amounts of energy in cultivation and processing, and the carbon cost of this energy is more than offset by the carbon sequestered by the plant itself. Straw bales also require less energy in their transportation, and at the end of their life they can be easily dismantled and left to rot.
Natural building materials also tend to be breathable - and must be used with breathable renders, plasters and paints. Breathable materials absorb and release water vapour, meaning that they regulate humidity levels well. When the air is humid, they absorb moisture; when the air is dry, they release moisture. This breathability circumvents many of the problems caused by water vapour in modern buildings, such as excessive dampness, condensation and mould growth.
A final point to make (whilst trying not to promote natural buildings as some kind of greenwashed eco-lifestyle-concept) is that many people derive enormous satisfaction from being in a building whose components have an obvious link to the surrounding world. People are pleased to know that the earth walls encircling them were dug from the ground beneath their feet, that the straw keeping them so snug was grown a few fields away, or that the trees holding up the roof inside have descendents growing outside.
So, if you decide you want a building made of natural materials, what are the possible choices? It depends what you want the building to do, and what materials are available near enough to the site for their transport to be sustainable.
In designing a building, several key factors are compressive strength, insulation, thermal mass and time and cost in building. Compressive strength refers to a material’s capacity to bear a load. Earth has a high compressive strength and straw bales have a lower compressive strength. Compressive strength is a limiting factor in the weight of your building, and weight is a limiting factor in the height of your building and what you have in it. So, how high do you want the building to be? Is the roof made of something light (like corrugated metal) or something heavy (like turf)? Will the building contain normal household objects, or heavy factory machinery?
Insulation refers to a material’s capacity to trap heat inside a building. Hempcrete and straw bales are relatively good insulators, earth and limecrete are relatively bad insulators. Is it important that the building is warm? Might the building get too warm? Will the building have a heating system or will it try and do without one?
Thermal mass refers to a material’s ability to store heat and release it. Earth has a large thermal mass, straw has almost none. So, if you have a constant low level of heating then thermal mass is less important. If high level heating is provided for a few hours a day, then thermal mass is needed to stabilise temperatures between heated and unheated hours. Thermal mass is a particularly important element in passive solar design. Passive solar design is the idea of building a structure that derives ambient heating from the sun, so that it needs little or no extra heating. In a passive solar design, you need a large area for solar energy to enter the building and insulation to prevent heat escaping the building, but you also need thermal mass to stabilise temperatures between the times when there is sun and the times when there isn’t.
I don’t want to argue that natural materials are a good thing per se; but I do want to explain their advantages, and also the contexts in which these advantages apply - there’s no point in super-insulating a building if you’re only going to keep tools in it and wood is not sustainable if it’s shipped half way round the world.

Earth as a Natural Building Material

Earth building means different things around the world. Sections of the Great Wall of China are made out of earth rammed into shuttering, prehistoric remains of earth brick cities are found throughout the Middle East, and earth brick remains the predominant building material in South and Central America. Earth can also be pressed onto wooden frameworks, as it has been for thousands of years in Africa and Europe, or just layed down in huge lumps and sculpted into wall shapes.
The key is clay. Clay is the binder that keeps the other components of earth (stone, sand, silt) together in a shapeable mass. Clay is an abundant material, but in parts of the British Isles where it's lacking, lime and chalk have also been used as binding agents.
Earth has developed "sustainable" credentials in the last couple of decades. It's true that the embodied energy of earth as a building material is very low, especially if it is extracted from the building site. It's not a fantastic insulator, however, so compensation must be made with a super-insulated roof, or with extra insulation in the walls. What earth provides in abundance, however, is thermal mass. When earth is used as a walling or flooring material, a massive heat store is created. This makes earth a very useful element in passive solar designs.
Earth has also developed a reputation for "healthiness". It will not give off any harmful materials, and as a breathable material it will regulate moisture levels in a building extremely effectively in combination with its natural plasters and renders.

Earth is durable. The oldest cob structures in the UK are 700 years old, and there is no reason they shouldn't last many centuries more. The critical factor is moisture. Earth buildings need to sit on a plinth to keep them out of direct contact with the ground, and the roof should have a good overhang to protect the walls from long periods of driving rain.
In the UK, the four traditional methods of earth building are cob, clay lump, rammed earth and wattle and daub.
Cob is simply 20-30% clay, 70-80% aggregates (sand and stones) and about half a bale of straw per tonne of mix. The clay binds the aggregates together to create a load-bearing material, while the straw acts as natural rebar, giving tensile and sheer strength, and also aids the drying and insulating capacity of the wall.The materials are mixed by hand, by animal, or with the backhoe of a digger, and the resulting dough-like mass is used to sculpt not only walls, but arches, chimneys and indeed any other feature that is needed. Cob is load bearing, with an average compressive strength of 0.77N/mm2, so wall thicknesses are usually between 450mm and 600mm, depending on the structure. Cob is currently enjoying a massive revival in the UK as a building material, partly because of its sustainable credentials, partly because it is a simple option for the self-builder and partly because it can be formed into shapes which are impossible with other materials.

Rammed earth, clay lump and wattle and daub are all similar in their composition to cob, though there are variations in the amount of clay used and the addition of other natural binders such as lime. Clay lump is simply cob made into bricks. The wet mix is put into molds and allowed to dry, not fired. The resulting blocks can be layed like bricks, with a clay slurry used for mortar. Because the density of the bricks tends to be higher than with cob, load bearing capacity is increased and walls can be thinner, but insulate less well. In rammed earth, the mix is wetted somewhat less than you would wet a cob mix, and then rammed into shuttering by hand or with pneumatic rams. Again, because the density is greater, you have greater load-bearing capacity but less insulation. Daub refers to a cob-like mix which is pressed onto a wooden framework, the wattle. In this type of building, a timber frame provides structural support, and the daub merely acts as an infill. For this reason, it can be very thin and quick to build, but again will not perform well from an insulation point of view.

Earth has been used for construction for at least 10,000 years, and 30% of the world's population live in earth homes. Earth's advantages as a building material are simple: it is everywhere, it is basically free and it is incredibly durable.

by Matt Muldoon of The Natural Building Company

Seminário_26Jan09_Univ. Minho_Restoration of the Bam Citadel after the 2003 Earthquake

Realiza-se no próximo dia 26 de Janeiro de 2009, no decurso do Seminário na Universidade do Minho, uma Conferência proferida pelo Professor Mehrdad Hejazi da Universidade de Isfahan, Irão, sobre os temas :

Restoration of the Bam Citadel after the 2003 Earthquake

Risks to Cultural Heritage in Western and Central Asia

http://docs.google.com/gview?attid=0.1&thid=11ed008d3b85053b&a=v&pli=1

Esta fotografia foi tirada antes do terramoto pela QuickBird satellite a 30 de Setembro de 2003

Esta fotografia foi tirada após o terramoto pela QuickBird satellite a 3 de Janeiro de 2004

Poder-se-á pensar que é um tiro no pé falar no blog da fragilidade sismica em Bam destas estruturas em terra, no entanto é preciso compreender que os edifícios em Bam foram, na sua esmagadora maioria construídos sem essa preocupação, e que muito provavelmente o nível de destruição e tragédia numa cidade construída em betão e tijolo sem cálculos preventivos em termos de sismicidade poderia ser até maior que aquele que observámos no Irão.

Temos sempre tendência para olhar o passado com os nossos olhos, o nosso conhecimento, os nossos conceitos, e muitas vezes consideramos esse passado como atrasado ou retrógado, olhamos para Bam e dizemos " estava-se mesmo a ver, era tudo em terra, se fosse em betõe não caía!" e depois ficamos espantados quando observamos obras fabulosas de engenharia sem o recurso ao betão e com séculos de existência e estabilidade, construidas por esse mesmo passado, e do mesmo modo a verdade é que edifícios em betão e ferro também caiem.

É preciso encarar a realidade e separar as questões, as novas construções em terra devem ter como premissa o cálculo e reforço estrutural sismico, não é novidade, não conheço aliás nenhuma das construções ditas normais que não o tenha, e este pode ser metálico, em betão ou noutro material que lhe confira a resistência necessária. A arquitectura de terra deve olhar para o Futuro integrando-se e inovando, orgulhosa da beleza do seu passado, mas com as ferramentas e tecnologias existentes no Presente.

O verdadeiro desafio em tudo isto, e creio que será debatido e demonstrado no Seminário é o de como recuperar Bam (porque este monte de terra tem um valor histórico inestimável), e é um desafio não apenas para quem lá vive, mas para arquitectos, historiadores, engenheiros, arqueólogos e construtores.

Há no entanto uma boa notícia, a terra das casas está lá toda! Se fosse em betão ia tudo pró lixo!

Seminário_9Jan09_Univ. Minho

O Prof. Daniel Torrealva da PUCP, no Peru, irá apresentar o seminário “SEISMIC BEHAVIOR AND INNOVATIVE REINFORCEMENT TECHNIQUES FOR EARTHEN BUILDINGS” no dia 9 de Janeiro de 2009, no Departamento de Engenharia Civil da Universidade do Minho, em Guimarães.

O seminário é gratuito mas a inscrição é obrigatória, de acordo com a informação anexa.

http://docs.google.com/gview?attid=0.1.0.1&thid=11eabfec73cf87fb&a=v&pli=1

Enviromentally friendly Earth Homes

Aproveitamos para colocar um pequeno artigo de opinião sobre Construção em Terra crua e Construções com Palha publicado no site http://our-greenhome.com por C. Bailey-Lloyd / Lady Camelot

Environmentally-Friendly Earth Homes
December 2, 2008 ·

What are “Earth Homes?” Earth homes are houses that are basically constructed from the earth. Some earth homes are built from adobe, mud, straw or even underground as an earth-sheltered home. Environmentally friendly, earth homes are easy to warm and cool and extremely energy efficient.
Adobe Earth homes are houses constructed from bricks comprisedof tightly compacted earth, clay and straw. Adobe earth homescan be naturally water proofed by using fermented cactus juice!
Earth sheltered earth homes are houses the are constructed underground - or at least mostly beneath the ground surface.

Surrounding soil is a superp and natural insulation which makes these homes cheap to heat and cool. Usually installed in awell-drained hillside, earth sheltered homes have a skylight window that can fill the home with natural sunlight. Although costs may run a bit higher than conventional home construction,earth sheltered homes are a good, long-term investment as lowered maintenance and energy savings make up the difference.
Straw Bale earth homes are making a comeback as well. Straw bale earth homes are obviously constructed of straw and grass, are energy efficient, and can cut material building costs by as much as fifty percent.
Earth homes, such as Cob Houses are built from clay-type lumpsof soil, sand and straw. Similar to the adobe homes, except cobearth homes do not use bricks or blocks. Cob homes have walls that are sculpted into smooth forms. Again, very energy efficient, cob homes are well-suited for the very cold climates and deserts.
Rammed earth homes may have over 18-inch, thick walls that are made from a comcination of dirt, sand, cement and water. Energy conservative, rammed earth homes have the appearance of bungalow-style charm and help keep the house warm in winter and cool in the summer. Additionally, rammed earth homes may last hundreds of years.

Why build an earth home? Earth homes conserve energy, and in most cases are easier to maintain and can endure for years to come.
As we embark on a strange, new age and global warming continuously on the rise, doesn’t it make sense to construct your new custom home as an earth home?

©2004 - All Rights Reserved Environmentally-Friendly Earth HomesC. Bailey-Lloyd / Lady Camelot
Author: C. Bailey-Lloyd/LadyCamelot

Cal_Vol.II

"
(...)
Aplicações Normais e especiais de Cal:
Conforme anteriormente exposto, da hidratação da Cal resulta um produto (Leite de Cal) que se divide em dois, fundamentais: Água d Cal e Pasta de Cal. Ambos se aplicam directamente na construção da forma supra descrita.
No entanto, a sua combinação com outros produtos permite uma aplicação mais abrangente, como base da Realização de Argamassas: consiste na utilização da pasta de cal como ligante, na utilização da água de cal como amassadura, adicionando-se um inerte (areia) de granulometria conforme à finalidade da argamassa.

Argamassas Bastardas:
Neste capítulo, existe a possibilidade de na realização da argamassa juntar um pouco de cimento convencional, o que permite acelerar o tempo de presa, obtendo-se uma argamassa com as propriedades básicas das argamassas de Cal, mas com alguma “rapidez” inerente ao cimento (também, infelizmente, notada na sua inferior durabilidade). Designa-se este tipo de argamassa por “argamassa bastarda”.

Cal Hidratada com Óleo:
Um dos “segredos” mais bem guardados inerente à preparação e aplicação das argamassas de Cal reside, justamente, nos aditivos que se podem utilizar para obter argamassas com características melhores para cada tipo de utilização.
A sua realização remonta à antiguidade (Vitrúvio, Sec. I aC, Livro II, Capt. V), sendo a Cal o ligante fundamental de todas as construções da antiguidade, designadamente das construções Romanas.
A utilização de uma determinada quantidade de óleo no processo de hidratação da Cal produz uma espécie de betume, que ancestralmente se designava por galagala. Quando misturado este betume com areia e água, obtinha-se uma argamassa com excelentes qualidades para assentamento de alvenarias ou realização de rebocos.
A fortaleza de Ormuz, cuja construção foi ordenada por Afonso de Albuquerque no Sec. XVI, é um exemplo da utilização corrente deste tipo de argamassa, em acréscimo, a partir de Cal obtida de conchas variadas sobretudo, de ostras, como ligante das pedras de arenito vermelho com que a fortaleza foi erigida.

Os ventos fortes predominantes no local motivaram a erosão dos arenitos, permanecendo as juntas, actualmente, 400 anos depois, em relevo: pela dureza adquirida e extraordinária resistência da argamassa não foram erudidas pelo vento – caso típico em que a argamassa prevaleceu sobre a alvenaria. Fenómeno em tudo idêntico se pode verificar no anfiteatro Romano de Mérida (Emérita Augusta), salvo não ser conhecido que a Cal subjacente tenha, neste caso, sido hidratada com óleo – embora tudo leve a crer que sim. A diferença em relação a Ormuz, é que no caso de Mérida não estamos perante 400 anos, mas sim ... 2000 !

Em todo o caso, inúmeros estudos e exemplos demonstram a enorme durabilidade e dureza, além de salubridade, das argamassas de Cal Hidratada com Óleo, importando apenas registar que este tipo de Cal oferece as seguintes propriedades e características:

1. Enorme resistência e durabilidade
2. Grande plasticidade, sendo facilmente trabalháveis e aplicáveis em obra
3. Grande aderência às superfícies, não descolando facilmente durante a aplicação
4. Ausência de fissuras durante a secagem e endurecimento, ao contrário das argamassas
de Cal normais
5. Permitem a respiração da construção, seja por aplicação no reboco, seja na junta da alvenaria. Este aspecto é fundamental, pois impede a condensação de humidade no interior das casas, tornando os interiores sãos.

A cal purifica o ar, porque devido à sua composição química, absorve o dióxido de carbono durante o processo de carbonatação da Cal. De facto, a Cal empregue em construção encontra-se hidratada ou extinta, isto é, na forma Ca (OH)2. Quando é empregue em construção sob a forma de argamassa, o seu endurecimento resulta da absorção de dióxido de carbono para que a sua transformação em carbonato de cálcio ocorra. A este processo (de endurecimento) se dá o nome de Carbonatação:

Ca (OH)2 + CO2 = CaCo3 + H2O
Processo Químico em que:

Cal Hidratada Dióxido de Carbono Carbonato de Cálcio Água (que se evapora)
6. È hidrófuga, isto é, preserva a parede da humidade exterior, combatendo a formação
de sais na alvenaria
7. É polivalente, pois tanto pode ser aplicada como argamassa de cal AÈREA (presa em contacto com o Ar) como numa argamassa de cal HIDRAULICA (presa em contacto com água ou ambiente húmido)
8. A Cal é um produto ECOLÒGICO porque a sua produção ou fabrico resulta de uma Calcinação a temperaturas de 600o C a 800 oC, que se obtém por queima de lenhas normais, e ao longo da sua vida, absorve CO2, contrariamente ao cimento, que se obtém a temperaturas não inferiores a 1450oC, o que implica a queima de combustíveis fósseis bem como uma enorme libertação de CO2 para a atmosfera (a produção de uma tonelada de cimento origina a libertação de cerca de uma tonelada e meia de CO2 para atmosfera!).
9. A nível estético, nada se compara à textura, cor, brilho de uma superfície rebocada e caiada a Cal, pois os micro cristais presentes na argamassa e na caiação, bem como a normal irregularidade do trabalho, permitem a luz ser reflectida com matizes suaves e subtis na mesma superfície do mesmo reboco, contrariamente à pintura com tintas industriais, em que a subtileza não existe.
10. A cal envelhece com dignidade, isto é, o seu processo de degradação é permanente e subtil, acontece por matizes, e se na realização do reboco, for desde logo incorporado o pigmento de cor da caiação final, o processo de envelhecimento é suave e virtualmente pode ocorrer de forma contínua ao longo de séculos sem que a edificação perca dignidade e aparência.
Cal Hidratada com Óleo e outros aditivos:
É comum aditivar à Cal aditivos de cor (pigmentos) seja para cal em pasta seja em leite de cal para caiação, aditivos desejavelmente resultantes de pigmentos naturais tais como, por exemplo, os óxidos de ferro, que resultam na gama de vermelhos a amarelos tão frequentes na nossa arquitectura tradicional.

Notei como exemplo único, na região do Douro e nos anos que ali trabalhei, que a mistura das cascas das uvas, após a sua retirada do lagar, na altura da hidratação da cal, dotavam a Cal de uma cor fortemente escura, vermelha tinta, que posteriormente, após a decantação, produzia ora uma argamassa ora uma tinta de caiação de cor púrpura, muito rara. Este método foi-me ensinado por um velho artesão da Quinta de Vargellas, já falecido, e nunca o encontrei noutro local, nem qualquer outra referência à sua utilização.
Recentemente, análises químicas aos rebocos hidráulicos do sistema de canais da Pont Du Gard, na Provença Francesa, revelou que no processo de hidratação da Cal teriam sido misturados Figos Tintos esmagados.
A Figueira possui uma seiva, (que toda a gente conhece como leite de figueira) que se encontra também na casca dos figos, e que reagindo com a temperatura elevada, além de “corar” a argamassa para a intrigante cor vermelho-tinto que ainda hoje possui (2000 anos depois), motiva que a substância leitosa da figueira (da família do Látex) emulsionada com a argamassa, lhe dê características de total impermeabilidade e aspecto quase vitrificado, de enorme dureza. Durante muitos anos, o mistério da dureza e da cor da argamassa de aspecto quase vítreo que revestia o canal de condução de água deste monumental aqueduto, era um mistério.

Afinal, eram apenas... figos. A aplicação criteriosa de substâncias naturais pode conduzir a produtos de qualidade incomparável, que nem a mais avançada das indústrias actuais pode oferecer.
(Qual a marca industrial de aditivos hidrófugos que oferece... 2000 anos de garantia ?)
Múltiplas experiências podem ser realizadas, embora na prática o mais comum seja encontrar
aditivos com a finalidade de pigmentar a Cal.
É sabido que diversas substâncias interagem com a Cal, proporcionando-lhe qualidades idênticas de Cal Hidratada com óleo, desde que aditivadas durante o processo de hidratação, tais como:
Mais frequentes e actuais:
· Velas de sebo de carneiro
· Óleo de Linhaça
Outrora utilizadas correntemente:
· Azeite
· Borras de Azeite
· Outros Óleos vegetais
· Óleos Animais (de Peixe, de Baleia, etc)
Por razões evidentes, não se recomenda a utilização de óleos animais na actualidade.

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Fonte: http://www.jlu.pt/downloads/NORMA_CAL.pdf

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