CONSTRUCTION MORTARS: A 10,000 YEARS STORY
By Carlos Duarte
Vice-President of EMO and President of APFAC – Portuguese Association of Mortar & ETICS
Lisbon, February 2013
1. The importance of Fire
Stone, mud and wood have always been available to the Man on our planet. With the help of rudimentary tools, Man could transform the stone and the wood, making these natural construction products more suitable to his life.
However, a Mortar to bind the stones, keeping them stable and weathering resistant, was not yet available. Mud could give a little help, but it is not strong enough to defy the weather aggression. Caves were an excellent shelter. However, without fire, Man could not protect his family to animal attacks and to cook food.
2. The discovery of Lime
The discovery of fire happened many times, in many places of our planet. However, the know-how about creating and controlling fire could not be transferred, remaining confined to small areas. In certain locations, a fire could start in a forest due to trees being struck by lightning. This natural phenomenon was a mystery for our ancestors and fortunately a source of free fire.
Once the control of fire was achieved, that is, making fire and maintaining it alive, everything starts changing for Man: besides cooking his meals, fire was a protection for animal attacks. In fact, making a fire at the entrance of his cave, the tribe was safe while resting and sleeping.
The following assumption is well accepted: just imagine a family living in a limestone cave some hundred thousand years ago. Every family member took great care of the fire at the entrance, feeding more wood to prevent its extinguishing.
Meanwhile, the slowly but continued action of fire on the limestone was causing visible changes on the stone, forming quicklime. This way, when it rained, our ancestors discovered that the stone close to the fire was changing after a violent reaction with water and consequently dripping a white liquid.
Probably, Man used the white liquid (milk of lime) to make his first drawings in his cave. Mixed with the blood of a goat that he had just hunted, Man could get different colour tones for his drawings. Thousands of years later, this natural phenomenon was used to make Lime.
3. Lime: a very peculiar binder
Much closer to our era, about 10,000 years ago, a builder in Yiftah'el loaded his kiln with limestone and wood and let it burn for several days. The operation was finished when no smoke was coming out of the chimney.
The next step was dangerous, requiring his skills to achieve the correct result: he had to perform the extinction of the burnt stone (hydration with water), causing a violent exothermic reaction. The extinction phase could take very long time (months or even years) to guarantee a perfect Hydrated Lime, without traces of Quicklime.
After evaporation of the water excess, the builder made a remarkable construction product named Hydrated Lime, a simple white powder that mixed with sand and water was the main binder for Mortars during millenniums in all the construction works made on Earth. Lime Mortar would harden, ensuring the joining of the stones in a wall or pavement, as well as the rendering of a wall.
During thousands of years, all over the planet – limestone is a very common rock – Lime Mortars benefited of much research and developments, most of them made by ordinary bricklayers and builders. Additions like pozzolans, brick dust and other available materials were used to improve Mortar properties. Vegetable and animal fat were used to achieve better workability, animal blood to give colour, seashells, bones and teeth, whale oil, and many others. Even oysters, as a source of calcium, have been used to make Mortars.
Lime is considered a very peculiar binder for many reasons. In terms of environmental contribution, the Life-cycle Lime can be described as follows:
i) During the calcination phase, the limestone suffers decarbonation, releasing CO2 to the atmosphere (together with CO2 formed by fuel combustion). Lime oxide or Quicklime is formed, accordingly to the chemical reaction: CaCO3 -> CaO + CO2.
ii) Next phase is hydration or extinction of the Quicklime, following an exothermic reaction: CaO + H2O -> Ca(OH)2
iii) During the hardening phase (carbonation), part of the previously released CO2 is absorbed, accordingly to the reaction Ca(OH)2+ CO2 -> CaCO3 + H2O.
4. Natural Hydraulic Lime: another extraordinary binder
When compared to Lime, Natural Hydraulic Lime (NHL) is a young binder (less than 300 years old). John Smeaton (England, 1724–1792) pioneered the use of NHL in the Eddystone Lighthouse (1756, England).
This lighthouse was very important to navigation. Before commissioning the new lighthouse to Smeaton, the previous wood lighthouses went on fire because the lightning source was fire, and the combination of fire, wind and wood is not a safe choice.
Smeaton, a distinguished Civil Engineer, decided to construct the new lighthouse with granite blocks prepared in the coast and transported to the lighthouse location in rough waters, some 20 km from the shore. He needed a hydraulic binder and developed a sort of Hydraulic Lime for the job, as well as a “dovetail joint” to mechanically join the granite blocks together.
Smeaton’s lighthouse remained operational until 1877, when it was dismantled and re-erected ashore. It can be visited nowadays as a milestone of the English Civil Engineering. Smeaton’s research work on Hydraulic Limes was followed by the well-known French Louis Vicat (1786–1861) who made important developments on mortars and cements, which is the title of a compendium he wrote in 1837.
In Mortars and Cement , Vicat foresees the use of Factory Produced Mortars: ...Good preparation of mortar is an excessively hard thing to obtain in a work-yard: this difficulty has suggested to different builders the idea of making use of machines, and thereby rendering the manipulation independent of the will or strength of the workmen...
Natural Hydraulic Lime (NHL) is produced by burning argillaceous limestone in a kiln at 800-900 ºC, followed by controlled extinction of the burnt stone with water.
NHL shows a notable hybrid binder behavior: hydraulic and aerial. In fact, on the short term (28 days) NHL acts like Portland cement: mixed with water it suffers hydration (a fast reaction), although developing lower compression resistance. On the long term, NHL behaves like Lime, reacting with atmospheric CO2 suffering carbonation (a very slow reaction), increasing its compression and flexural resistances.
NHL by itself or mixed with Hydrated Lime (or, in certain situations, with a small quantity of Portland cement) is an extraordinary binder for Rehabilitation and Renovation of old buildings.
NHL is a quite rare product in European Union and also in the World. Accordingly to REACH , there are only 13 producers of NHL in the European Union (France, Germany, Italy, Portugal and UK).
5. Some historical milestones
This long story starts some millenniums ago:
i) 8,000 years BC: evidences found in Yiftah'el show that Quicklime was produced in very rudimentary kilns;
ii) 221–206 BC: started the construction of the Great Wall of China, using a Lime Mortar. However, accordingly to Chinese Scientists there are evidences that the additive used was sticky rice, making a super strong and weather resistant Mortar .
iii) Last Century BC/1st Century AC: Romans promoted great development in Mortar and spread this knowledge all over Roman Empire.
Marco Vitruvius, the eminent Roman architect, engineer and writer who invented, created and left for posterity the Architecture knowledge and building techniques of his time in the famous De architectura (The Ten Books on Architecture).
Nevertheless, other ancient peoples deserve to be mentioned because of their contribution, like the Nabataeans , who developed waterproof Mortars, an essential binder for constructing cisterns to collect the scarce rainfall in the desert.
Romans (and other civilizations) introduced the technique of using additions to Mortars, like pozzolans , brick dust, animal and vegetal fat, as well as different types of colorants.
Romans considered render mortars extremely important to protect the stone facades from the weather aggression. Those renders were named sacrificial mortars, being necessary to be renewed them from time to time.
A significant number of structures made by Romans can be visited today, like the Roman Aqueduct in Segovia (Spain), the Pantheon in Rome (Italy) and the Pont du Gard near Uzés (France).
iv) 1756–1759: Eddystone Lighthouse, Plymouth, England. John Smeaton’s research work on Hydraulic Lime.
v) 1820’s: Louis Vicat (France), following Smeaton’s work, continue the study of Hydraulic Lime. He is also known due to the apparatus he invented to determine the setting time of cement by measuring the pressure of a special needle (Vicat’s needle).
vi) 1824: John Aspdin, an ordinary English mason, patented Portland cement. The designation Portland is due to the color similarity of his new binder to the color of limestone from Portland Island, a well known source in England .
vii) 1857: 1st Portland Cement Factory in England, 33 years after the patent.
viii) 1893: a first patent on the manufacture and application of Dry-mix Mortars was published in Germany .
ix) Late 1920’s: first Dry Mix factory-produced Mortar in Germany (late 1930’s in the UK). However, only after the 1950’s, in Europe, job site mixed Mortars start giving place to factory-produced Dry-mix Mortar, due quality exigencies and requirements of a fast growing Construction business in Europe and USA.
x) 1989: publishing of the important European Directive of Construction Products, DCP (Council Directive 89/106/EEC).
Most of Mortar families are regulated by CEN Standards and obliged to CE Marking. The letters "CE" are the abbreviation of the French phrase "Conformité Européene" which literally means "European Conformity". CE Marking was not a quality mark, but a consequence of DCP, meaning that the product complies with the essential requirements of the relevant European health, safety and environmental protection legislation.
xi) 1991: a group of German and French Dry-Mix producers decided to found EMO, European Mortar Industry Organization.
xii) 2011: publishing of the European Construction Products Regulation, CPR (305/2011/EU-CPR), replacing the Construction Products Directive. It provides more clarification of the concepts and the use of CE Marking, introducing simplified procedures. CPR will be full effective after 2013.07.01 replacing DCP.
6. What’s next?
10,000 years after the builder and his kiln in Yiftah'el, patiently waiting for his batch of Quicklime, the changes are vast and Construction became a complex system.
What a long way from the simple chemical reaction CaCO3 -> CaO + CO2 to the following buzzwords and concepts:
Building Life Cycle, Carbon Stock Market, CDR–Construction and Demolition Residues, CE Marking, Decommissioning, Durability, Environmental Aspect, Environmental Impact, Environmental Performance, EPD–Environmental Product Declaration, Green CO2, Incorporated Energy, Life Cycle, Life Cycle Assessment, Nanotechnologies, Positive Energy Buildings, REACH Registration, Recycling, Reusing, Service Life, Social Aspect, Social Impact, Social Performance, Sustainability, Zero Carbon, and so on, and so on!
The utility and the need of such exigencies, measures, standards and registrations are out of discussion. But we should realise that occasionally they are difficult to understand (even for experts), expensive to accomplish (because of the tests costs) and sometimes unfeasible for small companies.
Under this scenario, the advantages of being Member of a National Association are evident and those advantages are strengthened if the National Association becomes Member of EMO, a Membership with Benefits for the Mortar Industry.
1 Today an archaeological site located in the Lower Galilee in Northern Israel.
2 Cf. page 205 of the Appendix. Reprinted by Donhead Publishing, Ltd, http://www.donhead.com/
3 REACH: European Community Regulation on Chemicals and their Safe Use, in 2010.
5 Cf. http://www.telegraph.co.uk/news/worldnews/asia/china/7785842/Great-Wall-of-Chinas-strength-comes-from-sticky-rice.html
6 Available, for instance, in: http://www.gutenberg.org/ebooks/20239
7 Cf. Professor Dr. Joseph Davidovits, http://nabataea.net/cement.html
8 Aka pozzolanic ash. It is a fine volcanic material discovered in Pozzuoli, Italy.
9 After the great fire of London in 1666, the city was rebuilt using limestone from Portland Island.
10 Cf. http://www.mbam.org.my/mbam/images/MBJ1QO6(pdf)/@DryMortar.pdf
11 CEN, European Committee for Standardization, http://www.cen.eu/cen/pages/default.aspx