Building limes for cultural heritage conservation in China
© Dai; licensee Chemistry Central Ltd. 2013
Received: 23 March 2013
Accepted: 3 July 2013
Published: 2 August 2013
Lime has been used as a building and decoration material for thousands of years in China. Recent research has focused on developing new air lime with higher bonding strength, grouts and restoration mortars etc. based on natural hydraulic lime, which is both chemically and mechanically more compatible with historic substances.
The most applied lime in China was, and is still air lime, and the traditional slaking and preparation technique has been passed over to the modern generation for most restoration projects. Optimum dosage of Tungoil to lime-earth as damp proofing barrier lies at app. 5 wt%. A kind of patented dispersed air lime modified with additives has been developed, which can be applied as a binder for restoration of traditional lime ornaments or lime paints. Natural hydraulic lime has been introduced into China from 2008 Recently, adhesives and grouting slurries based on natural hydraulic lime have been developed and applied for refitting and cavity filling of delaminated cultural surfaces with proven satisfaction.
The preliminary research works show, both air lime and natural hydraulic limes through modification of latest construction chemistry achievements can meet most of restoration requirements.
KeywordsBuilding lime Cultural heritage conservation Natural hydraulic lime Adhesive Grouting Restoration mortar
Basing on the research of lime materials in China over the past two decades, this paper summarizes some of the latest achievements in research and development of lime, especially natural hydraulic lime, for conservation and restoration of cultural heritage in China under the funding of several national and international research projects.
Traditional slaking and preparation of lime in China
Lime has been used as a building and decoration material for thousands of years in China [8, 9]. However quick lime was in most cases slaked wet, only in coastal region, quick lime kilned from oyster shells was slaked dry, but without any grinding. This may be one of the reasons why the term “hydraulic lime” was translated into China as early as 1950′s, but not understandable and applied by most technicians.
Like in Europe , hot lime is being also tried to restore natural stone architecture and ornament earthen elements. During restoration of Bell Tower Beijing in 2010, quick lime was slaked to form lime milk according to traditional lime slaking technique to seal voids and joints by pouring into cracks immediately after slaking. The subsequent expansion of freshly slaked quick lime milk compensates the shrinkage of pure lime grout.
Building lime standards in China
In 2010, new European building lime standard EN459-1, modified from previous version, was published . Comparing to old version, natural hydraulic lime (NHL), formulated lime (FL) and hydraulic lime (HL) under the category of limes with hydraulic properties has been clearly specified. Natural hydraulic lime, its use can be dated back to Romans , is a lime with hydraulic properties produced by burning of more or less argillaceous or siliceous limestones with reduction to powder by slaking with or without grinding. No other additions are allowed except grinding agents up to 0.1 wt%. Hydraulic lime is, however, a binder consisting of lime and other materials such as cement, blast furnace slag, fly ash, limestone filler and other suitable materials, but does not need to have a declaration of constituents. Formulated lime (FL), which is a new term, is a lime with hydraulic properties mainly consisting of air lime (CL) and/or natural hydraulic lime (NHL) with added hydraulic and/or pozzolanic material. To protect the user especially in restoration and conservation, formulated limes contain a constituent’s declaration.
The advantages of NHL are low strength; low content of water soluble salts, but it has also disadvantages, for example, not frost resistant if it is not completely carbonated. One of main disadvantages of HL is the fast hardening, which may cause tension cracking between historic substances and new materials. FL shall bridge the gap between NHL and HL.
In the USA, new ASTM standard for hydrated hydraulic lime for structural purpose was also published in 2009.
Chinese Building Lime Standard JC/T 481-1992
Content of CaO + MgO,%, no less than
Content of unslaked residue (5 mm round-hole residue on sieve),%, no more than
CO2,%, no more than
Yield of lime hydrate, L/Kg, no less than
From 2009 laboratory tests and pilot production trials of natural hydraulic limes from various argillaceous limestones to limited scale have been launched , however until now there are no manufacturers of hydraulic limes in China, therefore currently all natural hydraulic limes for the research and application in China are imported either from France or from Germany.
Lime for surface refitting, grouting and colouring
There are a few research works carried out to develop grouting materials on the basis of natural hydraulic lime for structural purpose [15–18]. The results were controversy. It is however clear, due to high shrinkage, the mixture of natural hydraulic limes only with water is not suitable for grouting. They need to be modified with help of modern construction chemistry. From 2008, a system of new adhesives based on modified natural hydraulic limes has been developed. The system consists of 2 products; the first one is an adhesive for refitting and emergency re-bonding, with pull-off strength on marble substrate of app. 0.5 N/mm2, after 28 days, can reach up to 1.0 N/mm2 after app. 180 days. Second one is a grout with excellent flow properties for injection and cavity filling. Both formulations are already patented in China [5, 6]. The practice to rescue Huashan Pictographs (Figure 1) and other natural stone monuments has proven their satisfied results. However, the durability and application under various climate zones need to be further studied.
Performance comparison of various dispersed air limes
Dispersed air lime, Type C
Dispersed air lime Type F
Commercially available dispersed lime from one German company
Solid content, wt%
10% (white marble powder)
7-day pull-off strength on marble substrate/ carbonization depth
0.75 N/mm2/≤1 mm
0.69 N/mm2/≤1 mm
0.28 N/mm2/3-4 mm
28-day pull-off strength on marble substrate / carbonization depth
1.45 N/mm2/3-4 mm
1.40 N/mm2/3-4 mm
0.31 N/mm2/7-9 mm
Capillary absorption coefficient (kg/m2•h0.5)
No chalking after 24 hours
No chalking after 24 hours
Chalking after 7 days of construction
Lime-based restoration mortar for green bricks
In the pilot project jointly launched by Beijing Institute for Ancient Architecture and Tongji University , a special restoration mortar for green bricks has been developed. This lime restoration mortar is formulated with low strength, lower than deteriorated green bricks, and higher water absorption capacity and shall function as the sacrificial layer to conserve historic substances.
This mortar is composed of app. 18 wt% NHL2 (Hessler Kalk Germany), app. 6 wt% calcium hydrate (CL), app. 75 wt% well graded crashed old bricks and limestone fillers and very small amount of Methyl cellulose, thixotropic agent, wood fiber, iron oxide pigments. All the components are premixed dry with help of dry mortar mixer than packed in 1 L containers. Conservators mix the powder with only water and/or small amount of iron oxide pigments to match individual stone on site.
Conclusions and discussion
Lime has been used as a building and decoration material for thousands of years in China, but today it is no longer popular in new construction industry. In future, lime materials will be mainly used for the maintenance, restoration and conservation of historic architectures and cultural heritage. Most applied lime in history was wet slaked air lime, which was used as binder for masonry mortar or decorative plasters optimized with aggregates, fiber and natural organic resin (for example Tungoil). Lime is also used as stabilizer to consolidate earth in historic construction of city wall, roofing and earthen architecture. The traditional skills to slake and prepare lime are still being promoted in most of restoration and conservation projects.
Despite the same long history in the use of lime, China is far behind of Europe in the research of lime in modern times. Due to the wet slaking and lake of grinding technique, the ancient Chinese did not realize the hydraulic properties of limes, which can only be observed through dry slaking with or without grinding. Until 2008 natural hydraulic lime was introduced from Europe into China and has been researched comprehensively, but exclusively for conservation of cultural heritage. Adhesives, grouting slurries, restoration mortar for natural stones and kilned bricks (from traditional green bricks to firebricks) based on modified natural hydraulic limes (may be defined as formulated lime, FL, according to EN459-1/2010) have been developed. With help of modern construction chemistry achievements, natural hydraulic limes can be modified to meet almost all kinds of requirements for conservation and restoration of cultural heritage. The new challenges will be grout to seal cracks from adobe and earthen masonry.
New research works in the future will be focused on comprehensive understanding the traditional Chinese lime skills scientifically (for example project granted No. 2012BAK14B05) and code of practice to transfer traditional lime skills to new generation.
More efforts will be done to understand the performance of lime under different climate and long term durability. Preliminary researches have shown, lime restoration mortar with the same formulations have different strength, NHL-based restoration mortar for green bricks has high strength in Beijing climate than in Shanghai. The reasons are not clarified.
About the author
Dr.rer. nat. Shi-bing Dai (1963- ), Professor at College for Architecture and Urban Planning Tongji University, Director of Architecture Conservation Laboratory, specialized in building restoration and monument preservation.
This article is completed under the financial support of China National “Twelfth Five Years Key Research and Development Project granted No. 2012BAC11B01-2, the Architecture Conservation Laboratory (part of the of the Key Laboratory of Ecology and Energy-saving Study of Dense Habitat, Tongji University, Ministry of Education, PR China). The author thanks Wang Jinhua, Wang Yunfeng, Hu Yuan, Zhou Xiao, Dr. Li Li from China National Academy for Cultural Heritage in Beijing for fruitful collaboration within research projects on natural hydraulic limes and their application to consolidate stone monuments, which are funded by Ningming Cultural Bureau, Guangxi Autonomy and China National Bureau for Cultural Heritage. The author thanks also Dr. Huang Jizhong for collaboration of the research project in southern Shanxi Province. The author expresses deep appreciation Hang Yang, Zhang Tao from Beijing Institute for Ancient Architecture for constructive discussion on restoration of stone and green brick. The author also acknowledges Zhang Debing, Chen Guojun, Hu Zhanyong, Zhu Shangyou and Zhou Yuee for most of the laboratory testing and mock-ups in collaboration with Shanghai DS Building Materials Co. Ltd..
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