The Long-Term Efficiency and Compatibility of Hydrophobic Treatments in Protecting Vulnerable Sandstone at Arbroath Abbey (Scotland)

Round 1

Reviewer 1 Report

In the current form the manuscript does not clearly respond to the title and aims and should be revised. In short, the authors should better support what they report in the abstract: “We also compare these field results with lab-based experiments in an attempt to assess more quantitatively the suitability of such treatments in protecting porous building sandstone. Our data suggest that although the treatment was successful overall in reducing the rate of decay, the degree of success was variable due to the inherent heterogeneity of the building sandstone.”

 

Specific comments are reported as follow.

The manuscript is organized in two parts: the first one investigates the residual protection properties of a past treatment made on the Arbroath Abbey in Scotland with the Brethane product and investigations are performed  through on-site moisture mapping of the previously treated area. This part, with reference to the effective and sustainable methodology adopted, may have an interest in the context of in situ monitoring of conservation treatments, where research is oriented to find suitable procedures at this purpose. As regard the understanding of long-term behaviour of conservation products, the Bretane product performance has an interest limited to this case study, as it “never became commercially available, however, due to health and safety  concerns regarding the presence of lead [3]. “, unless its study provides indications to be taken into account for new treatments. 

The second part, which mainly deals with the manuscript, pays attention to the laboratory assessment of the performance of a new protective treatment for the sandstone of the Arbroath Abbey and focuses on the different results having relation with the inherent variability of the stone, which is documented by the characterization of two ashlars from the artefact.

The two parts do not show an adequate correlation, as the title of the manuscript would suggest and in spite of the aims that authors report in lines 49-52:  “As part of this study, we have re-examined one of the treated areas in order to investigate the long-term efficiency of the hydrophobic treatment, thus providing insights into the potential suitability of such treatments at the Abbey moving forward.” and lines 67-69: “The aims of the study were to assess, firstly, how Brethane specifically has performed over time at Arbroath Abbey and, secondly, the suitability of a currently available hydrophobic cream as a means of protecting the Abbey sandstone moving forward.“ It is not clear  in the manuscript which insights the assessment of the previous treatment could provide and how they relate to the laboratory-based investigations concerning the new hydrophobic cream. Please, better argue this point in the aims in the above reported lines, as well as in the discussion of results and conclusions.

In this regard, section 4.1 needs to be revised. Apart from the residual hydrophobicity detected on site, it is not clear which is the state of conservation of the treated stone on the Abbey, whose evaluation can contribute to understand the issues of the previous treatment and eventual limits useful to better address new conservation treatments. Is it only affected by delamination and blistering, as reported in lines 276-277? Please, describe better how the decay patterns affect the surface in treated and not treated parts and which indications can be derived  about the previous treatment. In lines 280-281, the authors report that  “the treatment does not appear to have accelerated weathering of adjacent untreated stone. “ Please, develop this observation. Why such an effect could be expected?  

Final Discussion and Conclusions need to be revised in Lines 508-525. In particular, please, according to previous comments, better explain in which way  “combined field-based moisture analysis and lab-based stone characterisation tests led to better understand the efficiency of hydrophobic treatments in protecting stone-built heritage” and how “they helped provide more context to the problem under investigation.” 

“Interestingly, both sea-derived salts and rising damp (see above) are present at Arbroath Abbey,  yet the brethane treatment appears to be performing well. “ Which is the relevance of these results in correlation with the new treatment studied in lab conditions, which is different from brethane?

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

General considerations: 

Authors present a study concerning the efficiency and durability of the sandstone of hydrophobic protectives. Correlation between decay detected in situ and aggravated decay through salt crystallization test is not addressed and it must be the core of the research. The author should conduct in-situ Vp measurement analyses and cross-reference the results with those obtained in the laboratory. Additionally, it would be beneficial to include a map similar to the one depicting relative moisture levels. This map will enable both the author and readers to comprehend the extent of decay following 40 years of weathering exposure. This additional and crucial approach can provide a deeper understanding of the environmental conditions and their impact on the material's decay.

 

In the current form, the article is not suitable for publication.

 

 

Below some point to point suggestions to improve the text:

 

Line 55: "Coatings are typically hydrophobic and aim to prevent moisture ingress". Coatings aim to reduce the wateringress in liquid form including, beside moisture: rain, saline solutions and other accidental sources of water (or any "liquid"). Coatings are also bioprotective, anti graffiti etc. Please rearrange the sentence.

 

Line 62: and flexural strength of the surface . This is a randomness, delete or write a generic "mechanical strength of materials".

 

Fig.1: please label the figures as a), b) and c). two "a" cannot be present. Do you have a higher resolution image of the site?

 

3.9 Paragraph, Durability.  

Why did you perform this internal protocol instead of following the EN 12370 for salt crystallisation resistance? I suggest authors to explain the benefit of applying a protocol different from the standard. In literature, few researchers have modified/improved the procedure to evaluate the effect of salt attack on stone and on coatings durability. Here some work you can refer to for improving the paragraph:

1) EN 12370:2019 - Natural stone test methods. Determination of resistance to salt crystallisation.

2) https://doi.org/10.1016/j.cscm.2022.e01572 

3) https://doi.org/10.1007/s12665-021-10064-3

4) https://doi.org/10.1617/s11527-018-1309-6

5) https://doi.org/10.1016/j.porgcoat.2016.07.018

6) https://www.researchgate.net/publication/311584092_Effects_of_Adding_Nanosilica_on_Performance_of_Ethylsilicat_TEOS_as_Consolidation_and_Protection_Materials_for_Highly_Porous_Artistic_Stone

 

4.1 Decay patterns: I suggest you write the definition of the pattern of the ICOMOS Glossary. This  could be an added value to your inspection as the images are exemplary!

 

Lines 277-279. I do not understand, are these data supported by in situ analyses, besides the moisture content?

 

Line 293: “which can often be associated with buildings which have a cemetery adjacent to them [23].” Please delete this sentence.

 

Line 266-298. This section under study is not sufficient to evaluate the durability of the treatment. Author should investigate different (even reduced) surfaces at different heights. The justification is not reliable. In case of restoration, a widespread and accurate investigation of the degree of absorption of the wall would certainly be required because the sandstones are heterogeneous. How did you apply water? Which is the method?

The boundary is not so evident. The evident boundary is on the right, where the purple is significantly detached from the green along the same height. 

 

Line 307: there is a double point after “probe head”

 

Fig.7. A semi-quantitative analysis is needed beside the peaks. 

 

Line 354: an image under SEM-EDS or optical microscopy (color image) is needed to better represent the petrography of the stone.

 

Fig.9 this is obvious. I suggest you delete this graph. Which additional value it gives to the interpretation? Just keep table 4

 

Tab.4: Bulk density is expressed in g/m³. Do you mean g/cm³?

Regarding standard deviation, you must insert the symbol ± before the number, es. SD= 8  ± 4.16

 

 

Fig.10: please add the symbol’s information as legend in the graphs and delete from the caption. For the reader it is easier to interpret.

 

Line 495, “material loss, decay”. Positive values are also calculated. It means that a gain in mass was calculated. Please, in y axis, instead of “decay (%)” refer to a “mass difference (%)” or a “weight difference (%)”. Another alternative is the Delta Mass (%)”. 

 

Table 6. Please just mention in the text that it is an average of 6 samples. It is not necessary to add this information in the table since you have used 6 cubes for all the tests.

 

 

Conclusions: 

Please strengthen the conclusions according to the corrections and the suggestions recommended in the general considerations.

minor spelling required

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have responded to the previous comments, but their answers confirm that they could not use the results of the field check, in order to add additional elements for the evaluation of the new treatment, given that the two products are different, so that the new one could have a behaviour on site which is different than the previous one.   

Therefore, the two  parts of the manuscript yet remain not correlated: the lab part could withstand without the field study. The latter rather documents a previous treatment in the specific case of the Abbey, but any contributions coming from the combination of field and laboratory studies in evaluating the new treatment issues, which is the main part of the manuscript, is provided.  Therefore, in my opinion, the title is misunderstanding, as it suggests a combined approach -which is a key topic attracting increasing attention in conservation studies - but it is not exactely developed in the study to overcome the limits of a lab study. I would suggest to change the title as follow:  The long-term efficiency and compatibility of hydrophobic treatments in protecting vulnerable sandstone at the Arbroath Abbey (Scotland). 

One more comment: in section 4.1 the authors have better described the state of conservation of the treated and untreated stone and it results that “ decay patterns are consistent across treated and untreated areas of the façade. This may suggest that the treatment has not altered the petrophysical properties of the stone as the response to weathering is the same as untreated stone.” 

This finding is relevant to the compatibility of the previous treatment, as it does not alter negatively the petrophysical properties of the stone, and the field study  also testifies that the hydrophobic properties are preserved. But a question raises: If the weathering of the treated and untreated stone is the same, which effectiveness of the previous treatment in protecting the stone in order to reduce the decay? Please, clarify.

 

Author Response

Please see the attachment. 

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

Thanks for your point to point revision. In my opinion, the manuscript is now fine.

Good luck!

Author Response

We thank Reviewer 2 for their comments which have strengthened the quality of the manuscript considerably.