The Protection of Building Materials of Historical Monuments with Nanoparticle Suspensions

Round 1

Reviewer 1 Report

The manuscript deals with the development and application of amorphous calcium carbonate and silica for the conservation of marble. The research is not innovative, as several researches on the use of similar compounds have been already published few years ago. It is also quite difficult to understand the innovation and novelty of this research. In addition, important requirements for the set-up of conservation treatments for heritage stone, such as color compatibility, changes in water absorption and water vapour permeability, contact angle, etc., were not taken into consideration by the authors. I think the data reported in this study need to be published together with results obtained on the application of the compounds on solid marble samples. 

In many parts of the manuscript, the authors do not explain and justify well the results they obtained. The manuscript needs to be checked by a native English speaker, as many sentences are unclear and with mistakes.

The introduction is lacking important information on stone conservation (requirements, working properties, etc.) and the advantages of using nanomaterials compared to traditional materials. The Authors dedicated more space to explain the methods used, instead of focusing on the most significant literature on this topic and explaining the novelty of their work.

In the methods, it is not described why powdered Pentelic marble was used, instead of solid marble, which would better simulate practical working conditions. The methods used to apply the suspensions to powdered marble can not be followed in conservation interventions, therefore I don’t think they are appropriate to study this type of treatments.

In the results, figures need to be enlarged, as it is often difficult to read the labels of the spectra. In Figure 2 the scale bar needs to be bigger too, and the figures needs to be reported at the same magnification for better comparison of the size. Figures 7a and 11 need to be better described, and they look very noisy. I suggest increasing the acquisition time during the analyses of these materials.

Author Response

Response to comments point to point

Author Response File: Author Response.pdf

Reviewer 2 Report

The work is a serious and robust investigation into the synthesis of nanoparticles for intervention in stone materials.
From the point of view of generation and characterisation of the nanoparticles it is correct. 
However, from a practical point of view, it presents some doubts.
The first is the translation of the results to the real application in monuments. If tests had been carried out on marble specimens or slabs, it would have been better than on marble powder.
On the other hand, it is not clear how they measure the sealing effect of the porosity and the deposition in the porosity is not visualised (MOP or SEM).
The authors should augment the introductory section with more references and discussion on practical aspects and previous application experiences in real cases. 
In the methods they should explain why they do not use specimens or plates and should more clearly state how they measure the pore volume before and after nanoparticle treatments.

Author Response

Response point to point to comments in the attached file

Author Response File: Author Response.pdf

Reviewer 3 Report

Abstract

Generally, the abstract contains a summary of what is in the paper and not explicit technical parts.

the authors show great confusion in the terms generally applied in the sector

erosion is a term for changes of physical origin, whereas for acid attack the term corrosion is more correct

the contest of corrosion by acid rain is not supported by adequate literature research.

introdution
the crystallinity of Pentelic marble reduces the exchange surface and therefore acid attack does not occur rapidly and subsequent dilution makes it almost impossible to initiate the reaction. 

Calcium hydroxide cannot be understood as a protector, but rather as a consolidant, since its reaction produces a form of crystalline net and therefore the term protective is misused.

the concept of penetrating the porosity of the stone reduces the surface but it is not clear in the text what is meant by retarder for what reaction?

experimental

it is not clear what is meant by table 1: what do the 5 tests at different concentrations produce as a final result?

result and discussion

the authors do not explain how they thik that the portlandite don't change, generally the transformation into calcium carbonate is very quickly,

under normal conditions this reaction always takes place within the first 28 days, much less so for compounds with a larger exchange surface area for carbonation.

gli autori non citano i numerosi lavori che parlano dell'influenza dei solventi organici nella formazione di vaterite e di aragonite al posto della calcite

the figures of pore distribution and marble dissolution are too small and unclear

conclusions

the authors theorise about an effect of reducing the reactivity of marble, but do not explain how this can be used directly on a monument and how the suspension can be distributed

Author Response

Resposne point by point to comments of the original submission

Author Response File: Author Response.pdf