31.3 New products – Nano Estel and its properties as a binder

10/07/12

After considering Nano Estel as a consolidating agent, we focus on nanosilica properties as binders for inert and pigments. Even in this case connections between the particles of the inert substrate or of the pigment and those ones of the silica are due to the evaporation of water. As previously discussed, we can obtain silica gel by changing the pH or adding water soluble solvents to it such as alcohol or acetone. The last one was discovered and implemented by the restorer and scientist Mr. Stefan Wörz. That way is particularly recommended to help detached fragments of plaster to adhere to the substrate and tie to each other. An application of nanosilica followed by another one of ethyl alcohol give prompt results. Suggested tools are: syringe; pipette; paint-brushes.


Nano Estel as a binder for inerts

As a binder Nano Estel shows properties that we cannot get from ethyl silicate, i.e. the possibility to create bridges between particles very detached from each other (we refer to a distance larger than 100 nm)
Up to now restorers have adopted two kind of binders for inerts:
  • Inorganic agents such as slaked and hydraulic limes. Side effects: Adhesion is not strong and the 'impasto' turns white when getting dry so the it is difficult to have a consistent chromatic adjustment
  • Organic agents such as epoxy and acrylic resins. Side effects: Transpiration and reversibility are compromised; the thermal expansion coefficient is different from that one of the substrate

Aware of those limitations, in the past they always put efforts to improve the properties of limes by adding organic ingredients; milk in the ancient times and acrylic and vinyl resins later.(For more information, refer to Bollettino CTS 25.3).

When using 
nanosilica binders the advantages are significant; we can get organic grouts characterized by good adhesiveness and water vapor permeability (because no organic resins inside). Moreover, the color is not spoiled by the whitening effect of limes.

Anyway, according to what experienced in our laboratories, it is always necessary to conduct a preliminary trial on the mixture of inert components we want to bind together. In fact 
nanosilica do not work for all the inert components at the same level. 
Scientific literature provides articles about 
nanosilica grouts applications. We would mention the consolidation of Maitreya temple murals, Leh [1], Tibet, and the restoration workshop of Nidaros Cathedral, Norway[2], and finally the putty decorations of the Cathedral of Freiburg where they mixed inert components (selected sized particles) with the nanosilica.


Nano Estel as a binder for pigments


Although sometimes it is necessary to patinate stone surfaces, there are not enough in-depth study about the advantages 
and limits of those methodologies. Nowadays two methods are in use, both with disadvantages.

1-Acrylic dispersions 
are user-friendly solutions but the resistance decays through time, and coat very often 'disappears', especially because of weathering and colors turn dull.

2-Silicate based paints 
offer better resistance and vivid colors. On the other hand, we have to take care the some negative effect of side-products such as sodium hydroxide and potassium carbonate (coming out from sodium silicate and potassium) that generate soluble salts as a consequence of carbonation with air.

The pigments dispersed in nanosilica medium retain good chromatic saturation and do not release lye or potassium carbonate (the amount of NaOH for stabilizing it is smaller than 0.5%)

Nano Estel has been chosen by AGORA Restauraciòn de obras de arte, Barcelona during the restoration project in the Cathedral of Barcelona, Spain, when they glazed some pieces of stones used for replacement. They got good the results in terms of chromatic consistency and resistance to friction and water sliding.

Conclusions
As a binder Nano Estel gives good performances. Anyway we are waiting for the weathering effects on those mortars and coatings through the time. Other interesting findings on pigments aggregation could come from the case study run at the University of Applied Sciences and Arts of Southern Switzerland (SUPSI), Lugano by the Francesca Piquè and Jacopo Gilardi, both teaching restoration and conservation of wall paintings and murals.


References
1. Nicolaescu A., Alexander A.; Red Maitreya Temple –Leh, Ladakh. Mural Conservation Project (Part 2) - A Tibet Heritage Fund Project. e-conservation magazine n°7Storemyr P., Wendler E., Zehnder K., "Weathering and Conservation of Soapstone and Greenschist Used at Nidaros Cathedral (Norway)”, Raphael Programme – European Heritage Laboratory. Report 2/2001,Restoration Workshop of Nidaros Cathedral, Norway

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