STONECORE is a European project to develop and apply nano-materials for the refurbishment of buildings and the restoration of sculptured artwork. Pictured throughout this article are buildings and artwork selected for restoration using nanomaterials developed by STONECORE partners to prove their viability in antique restoral.
In Europe, many buildings are made of either natural or artificial stone. Their normal life exceeds hundred years and refurbishment is necessary several times. With the age of a building, the importance of conservation increases and questions of the protection of cultural heritage become essential. Without any doubt, conservation of historical buildings, sculptures or wall paintings is the most challenging refurbishment task.
Leuben Castle, Germany
In all cases refurbishment requires materials which are compatible with the components originally used during construction. This is of essential importance for the consolidation of natural stone such as limestone, marble or sandstone as well as for mortar and plaster. However, the materials and components currently available do not fulfill these demands in all cases.
Austria: Marble sculpture from the 18th century
It is the main idea of STONECORE, a project funded in the 7. Framework Programme of the European Commission, to develop nanomaterials for the use in refurbishment and conservation. This requires the combination of fundamental and applied research in order:
• to develop nano-materials compatible to natural and artificial stone for refurbishment of buildings, monuments, fresco, plaster and mortar,
• to develop nano-materials usable for safe and environmental friendly removal of mildew and algae,
• to prove the effectiveness of the developed materials on site by means of non-destructive assessment methods.
Fortress Lilaia, Greece
Six SMEs, four universities, one public research organization and one governmental organization from seven countries have joined together in order to find a new approach for refurbishment of natural and artificial stone. The project, which has started in September 2008, will progress from investigations in the laboratory and small scale applications on trial areas, to the use of the materials that have been developed on selected objects in the field.
Ancient Theatre of Megalopolis
As a result of the STONECORE program, colloidal calcium hydroxide stable dispersed in different alcohols is available for restoration projects. Typical concentrations are between 5 and 50 g/L. The particles have sizes ranging between 50 and 250 nanometers(nm). Treatment of stones with nano-lime results in the formation of solid calcium hydroxide after evaporation of the alcohol. That converts into CaCO3 (calcite) in a way similar to traditional lime mortars by reaction with atmospheric carbon dioxide. The solvent evaporates without any residues. Compounds deteriorating stone or mortar are not formed. Apart from consolidation of stone and mortar, applications are possible for coating of different materials with calcium hydroxide layers, as adhesion promoter or as agent for paper conservation.
STONECORE restoration projects by country include:
Czech Rep.: Church Santa Barbara, Tower in Litomysl, Castle Pernstejn
Greece: Ancient Theatre of Megalopolis, Fortress Lilaia, Ancient Theatre of Sikyon
Austria: Marble sculpture from the 18th century, mud bricks from India
Germany: Church Hochelten; Leuben castle, Dahlen castle; Cathedral Xanthen, Aachen
IBZ-Freiberg, a STONECORE partner, has developed several nanomaterial products for stone conservation and restoration. Among them are:
CaLoSiL® - Nanolime, colloidal calcium hydroxide
CaLoSiL® contains in ethanol, iso- oder n-propanol suspended nanoparticles of calcium hydroxide. The stone consolidation is reached by formation of fine calcium carbonate crystals. The penetration is a multiple of normal lime suspensions. CaLoSiL® can also be used with advantage in combination with silicic acid esters (SAE). The additional formation of silicic acids and amorphous calcium silicate results in an additional consolidation of the material.
CaLoSiL® is applied in a flow coating procedure, by dipping, spraying or injection. It is important that the complete weathered zone of the stone down to the sound core is saturated with CaLoSil®, otherwise incomplete consolidation cannot be excluded. Fast evaporation of the solvent should be avoided. If necessary, the treatment can be repeated after between 8 and 10 days. The amount of CaLoSil® needed is dependent on the porosity of the material and the depth of weathering. Typical rates are at around 100 mL/m², however, extremely higher amounts are possible.
CaSoPaL® - Mold Remover
CaSoPaL® is the first mold remover, which combines the advantages of alcohol and lime. In ethanol or iso-propanol dispersed lime nanoparticles deaden the mold effective and lead to a structure consolidation of the plaster. CaSoPaL® contains no chlorine or fungicide. No residues are left in the treated areas. CaSoPaL® reacts alkaline, which results in conditions, where the mold formation is not possible.
DiLoCarB - Carbonization agent
The carbonization of plaster and mortar on the base of lime sometimes needs a lot of time, especially when the contact to atmospheric carbon dioxide is poor. DiLoCarB solves this problem. It contains an in ethanol or iso-propanol solved agent, which releases carbonate ions under alkaline conditions. Due to this a certain and fast transformation from lime to calcium carbonate is possible. The alcohol evaporates and no residues are left in the material.