27.1 New products – An atypical consolidant: Nano Estel

29/07/11

In the last few years we have noticed any remarkable progress in the field of science and applied technologies is strictly linked to the developing of nano technologies. Since 2008 CTS has introduced and promoted a nano-lime based grout produced by CSGI-Università di Firenze, labeled as Nanorestore® (for more information please refer to the Bollettino CTS n.14.2) This alcoholic dispersion of lime nanoparticles gained such a positive feedback from European market that the demand exceeded the production capability several times.
At present, CTS offers an alternative option, based on 
nanoparticles, called NANO ESTEL: a colloid system wherein the particles of SiO2 (in place of calcium hydroxide) are dispersed in water (instead of alcohol). The dispersed particles have a diameter not higher than 20 nm, below the declared size range of acrylic micro-emulsions(40÷50 nm) and nano-lime (200 nm). Because of the size of the dispersed phase, the product is very fluid, even if the dry matter represents 30% of the mix; so in most of the applications has to be dilute and silica has to be water down to below 10%. It is important to know that dozens of nano silica based products are available in different size and dispersion of the particles, in different grades of stability and content of additives, and so on. Just a few meet our needs in the field of restoration. Nano Estel certainly lives up to our expectations.

How could Nano Estel help us?
Following the evaporation of water, particles link to each other and generate a silica gel (the process is similar to the reaction of the ethyl-silicate), able to build bridges between detached particles of stone or plaster (consolidation effect), or link pigments on stone surfaces (patina), or tie together different kind of inert components (mortars for organic plastering)
Forming of the silica gel could be obtained not only by the evaporation of the medium (water), but also acting on three other parameters:

-changing the pH (once you mix with lime you get a quick setting)
-mixing with water-soluble solvents (alcohol, acetone)
-adding a salt (not recommended in restoration)


It is necessary to verify the influence of these parameters before dealing with the application.


Nano Estel as a consolidant.
The application of silica 
nanoparticles for consolidation is not completely new: some cases had been reported in Germany. An Italian restorer, Mr Martin Pittertschatscher, had already successfully adopted for the consolidation of a very porous plaster, adding also nano-lime in order to speed up the setting process [1]. We cannot consider nanosilica as a substitute for the ethyl silicate, because the second one can go deeper inside the substrate (due to the difference in size). In fact nanosilica particles are 'consistent' nanoparticles.


Nano Estel is for sure the best solution in those situations when ethyl silicate is not applicable, and those are:
  • Work is scheduled on a period of time shorter than 3-4 weeks. Note that is the minimum period for the ethyl silicate to set.
  • Temperatures below 10°C
  • The substrate to be restored is slightly humid
In fact Nano Estel can quickly set in 3-4 days!, as a water dispersion based product it does not suffer presence of water (condensation; level raising; rain….). It was regarded as a very reliable and effective product when used on an ancient Roman waterworks in Sesto Fiorentino.The findings of comparative tests show that reduction in permeability to water vapor is small, even smaller than that one of the silicate. It is necessary to underline that Nano Estel is a concentrated product; dry matter equals 30% and the active ingredients are supposed to be diluted with deionized water to 10-15%.
Concerning the restoration of plasters, an accurate diagnosis is required because there is still a lack of knowledge about interactions between that specific substrate and some grades of alkaline nanosilica products like Nano Estel.Tests on samples that simulate damaged surface of a fresco [2] demonstrated how the settings of the application and the porosity of the substrate are determining factors for nanosilica products. A comparative tests with nano-limes and acrylic micro dispersions revealed that all the products reinforce cohesion of the painting substrate and reduce the absorption of water.


Conclusions
Although outcomes are encouraging for these new substances, we need to push the research further in order to evaluate:
-the level of reinforcement that is required-the amount of the constituents in the mixture-the prevention of any chromatic change on the treated stone surfaces
A key-point about NANO ESTEL is related to safety. As an aqueous dispersion, this product is not flammable, nor toxic for the end users. That is cost effective in dealing with the risk assessment of any lab and shop floor and building yard. Transportation and storage are easy to manage as well.

You may also find pieces of information about Nano Estel as a binder on 
Bollettino CTS 31.3.


References
  1. Camaiti M., Dellantonio G., Pittertschatscher M.; “Restauro dello stemma affrescato del Cardinale Bernardo Cles presso il Castello del Buonconsiglio a Trento: nuove soluzioni per il consolidamento di intonaci dipinti distaccati dal supporto murario” Scienza e Beni Culturali XXIV, Bressanone, 2008.
  2. Costa E., Dei L., Gaetani M.C., Giovagnoli A., Ioele M. “Studio di consolidanti nanometrici per il consolidamento della pellicola pittorica dei dipinti murali” Atti Convegno IGIIC, Cremona, 2007.


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