Capillary Rise and Salt Weathering in Spain: Impacts on the Degradation of Calcareous Materials in Historic Monuments^†

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

Attached please find the comments.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

We sincerely appreciate your valuable comments and the time you dedicated to reviewing our manuscript. We fully agree with all your observations, which have significantly contributed to enriching and strengthening the relevance of this article. Below, you will find our detailed responses. We are also submitting the clean version of the manuscript, with the modifications highlighted in red to facilitate your review.

 

Point-by-point response to Comments and Suggestions

Comments 1: The theoretical link between capillary rise and salt crystallization requires empirical validation. Quantitative data (e.g., soil salt concentration, capillary rise height) from specific Spanish sites should be added to strengthen mechanistic credibility.

Response 1: Thank you very much; we fully agree with your observation. To address this point, we have incorporated the following paragraph into the revised manuscript (page 6, lines 238–249), as well as the new references in the References section.

This mechanistic framework is further supported by empirical observations in Spanish heritage contexts. Soil analyses from historic sites such as the Alhambra in Granada and coastal monuments in Cádiz have revealed electrical conductivity values exceeding 2.5 dS m⁻¹ in the upper 20 cm of soil, indicating moderate to high salinity levels capable of sustaining recurrent salt crystallization cycles [36, 37]. In these areas of southern Spain, capillary rise heights of up to 80–90 cm have been reported in clay-rich soils adjacent to historic foundations, allowing direct contact between saline subsoil moisture and porous calcareous stones [36]. Similarly, in the semi-arid region of Bardenas (Aragón), soil electrical conductivity values of 3–4 dS m⁻¹ were documented within the capillary fringe, with water ascending to approximately 70 cm in clay–loam profiles [38]. These quantitative findings provide strong empirical support for the role of capillary saline fluxes in the progressive deterioration of calcareous materials in Spanish historical monuments.

36. Rodríguez-Navarro, C.; Doehne, E. Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern. Earth Surface Processes and Landforms 1999, 24(3), 191–209. https://doi.org/10.1002/(SICI)1096-9837(199903)24:3<191::AID-ESP942>3.0.CO;2-G
37. Morillas, H.; Maguregui, M.; Gallego-Cartagena, E.; Marcaida, I.; Carral, N.; Madariaga, J.M. The influence of marine environment on the conservation state of Built Heritage: An overview study. Science of The Total Environment 2020, 745, 140899. https://doi.org/10.1016/j.scitotenv.2020.140899
38. Lorenzo-González, M.A.; Herrero, J.; Castañeda, C. A heritage dataset of soil and water salinity in Bardenas, Spain. Data in Brief 2024, 52, 110469. https://doi.org/10.1016/j.dib.2024.110469

 

Comments 2: Feasibility analysis of proposed solutions (e.g., capillary barriers) is absent. Include case studies on long-term efficacy and material compatibility, with cost-benefit comparisons for Spanish calcareous monuments.

Response 2: Thank you for this valuable comment. To address this point, we have included specific case studies demonstrating the long-term efficacy, material compatibility, and cost-effectiveness of proposed capillary barrier interventions in Spanish calcareous monuments (page 12, lines 462–481), along with the corresponding references in the References section.

These strategies have proven effective in practice, as demonstrated by recent conservation interventions in historic Spanish monuments. Field experiments conducted on a segment of the western wall of the medieval Muralla de Ávila showed that structural interventions aimed at limiting moisture ingress—such as waterproofing the adarve and improving surface and subsoil drainage—significantly reduced indicators of rising damp. Capacitance-based moisture probes (FDR) recorded a 30–40% reduction in volumetric water content over a six-month monitoring period, with treated sections consistently maintaining lower moisture levels than untreated controls [66]. The intervention materials, including membranes and drainage channels, were fully compatible with the original masonry and required only moderate investment, estimated by the IPCE at approximately €150/m², which is substantially lower than typical consolidation treatments (€1,500–2,000/m²). Similarly, a comprehensive study of several historic buildings in the old town of Seville reported that chemical capillary barriers, particularly silane-based injections combined with moisture-resistant coatings, achieved reductions in rising damp levels exceeding 70% over a five-year period [67]. These treatments were found to be minimally invasive, cost-effective, and highly compatible with limestone and lime-based mortars, while maintaining significantly lower moisture levels in treated areas. Together, these findings highlight the long-term efficacy, material compatibility, and economic feasibility of both physical and chemical capillary barrier systems as effective conservation strategies for calcareous heritage structures across diverse climatic regions in Spain.

66. Gil‑Muñoz, M.T.; Pérez‑García, P.P. An in situ experimental study of the hydric behaviour of a section at the western stretch in the medieval wall in Ávila. Ge-Conservacion 2021, 19(1), 280-291. https://doi.org/10.37558/gec.v19i1.997
67. Ortiz, R.; Ortiz, P.; Martín, J.M.; Vázquez, M.A. A new approach to the assessment of flooding and dampness hazards in cultural heritage, applied to the historic centre of Seville (Spain). Science of The Total Environment 2016, 551-552, 546–555. https://doi.org/10.1016/j.scitotenv.2016.01.207

 

Comments 3: Climate change impacts lack quantification. Incorporate predictive models (e.g., salt crystallization pressure under humidity cycles) or simulations to project future degradation rates.

Response 3: Thank you for this pertinent observation. To address this point, we have incorporated new references and a paragraph discussing recent advances in predictive modeling of salt-induced deterioration under climate change conditions (page 8-9, lines 358–379).

In parallel with these conservation-oriented measures, ongoing research has increasingly focused on predictive modeling approaches that integrate environmental variables and material properties to assess salt-related deterioration risks under diverse climatic scenarios. For instance, Cappai et al. [52] implemented a Mamdani-type fuzzy inference model that integrates environmental variables (e.g., temperature, relative humidity, solar radiation, and rainfall) with stone properties to simulate monthly probabilities of salt crystallization cycles. This model showed strong correlation with observed efflorescence patterns at a Mediterranean archaeological site and provides a non-invasive framework for assessing crystallization risk over time. In addition, thermodynamic formulations—such as those described by Flatt et al. [53]—allow the estimation of crystallization pressures based on salt supersaturation and environmental conditions, facilitating the evaluation of mechanical stress within the stone pore network during humidity fluctuations. However, Godts et al. [54] highlight that equilibrium-based models alone are insufficient, as actual deterioration risk also depends on the kinetics of salt crystallization and dissolution, as well as on the behavior of mixed salts frequently present in built heritage. Laboratory experiments by Benavente et al. [55] further support this approach by quantifying deterioration through mass loss in porous stones subjected to controlled wetting–drying cycles with saline solutions. Adapting these predictive models to regional climatic datasets would enable simulations of future degradation rates in calcareous monuments under various IPCC climate scenarios—standardized projections developed by the Intergovernmental Panel on Climate Change to represent alternative greenhouse gas emission pathways.

52. Cappai, M.; Casti, M.; Pia, G. Monitoring and preservation of stone cultural heritage using a fuzzy model for predicting salt crystallisation damage. Scientific Reports2024, 14 (1), 22671. https://doi.org/10.1038/s41598-024-73192-3
53. Flatt, R.; Mohamed, N.A.; Caruso, F.; Derluyn, H.; Desarnaud, J.; Lubelli, B.; Espinosa-Marzal, R. M.; Pel, L.; Rodriguez-Navarro, C.; Scherer, G.W.; Shahidzadeh, N.; Steiger, M. Predicting Salt Damage in Practice: A Theoretical Insight into Laboratory Tests. RILEM Technical Letters 2017, 2, 108-118. https://doi.org/10.21809/rilemtechlett.2017.41
54. Godts, S.; Orr, S.A.; Desarnaud, J.; Steiger, M.; Wilhelm, K.; De Clercq, H.; Cnudde, V.; De Kock, T. NaCl-related weathering of stone: the importance of kinetics and salt mixtures in environmental risk assessment. Heritage Science 2021, 9, 44. https://doi.org/10.1186/s40494-021-00514-3
55. Benavente, D.; del Cura, M.G.; Bernabéu, A.; Ordóñez, S. Quantification of salt weathering in porous stones using an experimental continuous partial immersion method. Engineering Geology 2001, 59(3–4), 313–325. https://doi.org/10.1016/S0013-7952(01)00020-5

 

Comments 4: Inconsistent terminology (e.g., "cryptoflorescence" vs. "subflorescence") creates ambiguity. Standardize definitions and ensure consistent usage throughout.

Response 4: Thank you for pointing this out. We have chosen to use the term "subflorescence" as the standardized terminology throughout the manuscript, as it is the most widely accepted and commonly used in current scientific literature. Moreover, this term has broader normative support and appears in recognized conservation guidelines, including those issued by ICOMOS and other heritage preservation institutions.

 

Comments 5: Limitations of non-destructive techniques (e.g., resolution constraints for high-salt stone) are overlooked. Address methodological boundaries and potential errors.

Response 5: Thank you for this important observation. We have incorporated the following paragraph into the revised manuscript (page 12, lines 486–500), as well as the new references in the References section.

While non-destructive techniques are essential tools for diagnosing and monitoring salt weathering in heritage structures, it is crucial to acknowledge their methodological boundaries and limitations. Techniques such as ground-penetrating radar (GPR), infrared thermography (IRT), and electrical resistivity often face resolution constraints—particularly when applied to stones with high salt content. Elevated salinity increases ionic conductivity, which can reduce the penetration depth of electro-magnetic signals in GPR and distort resistivity readings, potentially leading to inaccurate interpretations [71, 72]. Likewise, surface-based methods such as hyperspectral imaging and thermography may have difficulty distinguishing superficial salt crusts from deeper accumulations within heterogeneous substrates, thereby limiting their diagnostic precision [73, 74]. In addition, environmental factors, calibration errors, and ambient noise introduce further uncertainties that complicate data interpretation and reduce reproducibility [75]. For this reason, while non-destructive approaches remain valuable for early detection and risk mapping, their results should ideally be complemented by targeted destructive sampling or long-term monitoring where high diagnostic accuracy is required for conservation planning.

71. Blaschke, O.; Brand, F.; Drese, K.S. Quantification of Humidity and Salt Detection in Historical Building Materials via Broadband Radar Measurement. Sensors 2023, 23(10), 4616. https://doi.org/10.3390/s23104616
72. Pappalardo, G.; Mineo, S.; Caliò, D.; Bognandi, A. Evaluation of natural stone weathering in heritage building by infrared thermography. Heritage 2022, 5(3), 2594–2614. https://doi.org/10.3390/heritage5030135
73. Wang, X.; Cheng, Y.; Zhang, R.; Zhang, Y.; Huang, J.; Yan, H. Non-Destructive Assessment of Stone Heritage Weathering Types Based on Machine Learning Method Using Hyperspectral Data. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences 2024, XLVIII-1, 713–719. https://doi.org/10.5194/isprs-archives-XLVIII-1-2024-713-2024
74. Ren, Y.; Liu, F. A Novel Hyperspectral Salt Assessment Model for Weathering in Architectural Ruins. ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences 2024, X-2, 201–208. https://doi.org/10.5194/isprs-annals-X-2-2024-201-2024
75. Přikryl, R.; Snížek, P. Critical assessment of the “non-destructiveness” of Schmidt hammer test on monumental sandstones: a microscopic and microstructural approach. Journal of Cultural Heritage 2023, 59, 247–254. https://doi.org/10.1016/j.culher.2022.12.011

 

Comments 6: Figures 3–5 lack contextual details (e.g., location, time span). Annotate case studies with geographical and temporal data to enhance empirical relevance.

Response 6: We appreciate your comment regarding the need to contextualize Figures 3–5 with geographical and temporal data. However, the images presented come from our own archives and do not have complete metadata regarding their location or date of capture, which limits the inclusion of such information in the manuscript. This situation is due to incomplete recording at the time of capture during previous field campaigns.

 

Comments 7: The references should be expanded. Some new literatures might be help the authors to further deepen the understanding of reaction mechanism as well as newest developing in this field (Separation and Purification Technology, 372C (2025) 133463 Efficient Removal of Gaseous Elemental Mercury by Fe-UiO-66@BC Composite Adsorbent: Performance Evaluation and Mechanistic Elucidation DOI: 10.1016/j.seppur.2025.133463)

Response 7: Thank you very much for this helpful suggestion. We have expanded the reference list and incorporated the following paragraph to include the recommended citation (page 12, lines 501–511).

76. Zheng, Y.; Cheng, P.; Li, Z.; Fan, C.; Wen, J.; Yu, Y.; Jia, L. Efficient removal of gaseous elemental mercury by Fe-UiO-66@ BC composite adsorbent: performance evaluation and mechanistic elucidation. Separation and Purification Technology 2025, 372, 133463. https://doi.org/10.1016/j.seppur.2025.133463

Recent studies in materials science and environmental engineering have contributed mechanistic insights that help to deepen our understanding of salt behavior in porous substrates. For instance, Zheng et al. [76] investigated the adsorption mechanisms of gaseous elemental mercury using a Fe-UiO-66@BC composite, demonstrating how pore structure, surface functionalization, and physicochemical interactions affect adsorption efficiency and stability under dynamic conditions. Although primarily developed for pollutant removal, this research highlights the critical roles of internal porosity, ion mobility, and crystallization dynamics—factors that similarly govern subflorescence-related deterioration in calcareous materials. These parallels suggest that emerging composite materials and advanced characterization techniques may offer promising pathways for developing innovative protective strategies against salt-induced decay in built heritage.

 

We sincerely thank you once again for your constructive feedback, which has greatly contributed to improving the quality of our manuscript. We remain at your disposal for any further comments or suggestions you may have.

Author Response File: Author Response.docx

Reviewer 2 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

Dear Authors,

You made most of the suggested corrections.

Yours Sİncerely

Author Response

Dear Reviewer,

We sincerely appreciate your comments and the time you dedicated to reviewing our manuscript. We trust that the changes made have significantly contributed to improving the quality and clarity of the work.

Round 2

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

I am very satisfied with the updated and revised version of the manuscript. The authors have greatly improved the quality of the data presented and have addressed all my comments and concerns. I therefore recommend the publication of this research study in its present form.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

The article titled as Capillary Rise of Soluble Salts and its Effect on the Degradation pf Calcareous Material Used in Historıcal Monuments was investigated the effect of soluble salts in historical monuments. This topic of this review article is interesting. But a review article should be much broader and have much more detail. The article needs to be improved further by the authors.

If the article will only include Spain, Spain should be added to the title of the article.

The importance of historical structures within the scope of cultural heritage should be stated at the beginning of the introduction.  (ICOMOS).

Take care not to have sharp transitions between paragraphs

Please also add brief information about different types of deterioration in historical artefacts.

The article is not very interesting with only two visuals on two buildings. It is recommended that the visuals be increased too much. Please provide additional visuals from different structures.

You can also use some different references about this topic. https://doi.org/10.1007/s00339-008-4466-6: https://doi.org/10.3390/buildings12081200.

You should state which parameters you take into consideration and why, with their references in the introduction.

The number of references for a review study is quite low. Please expand the literature section.

The more comments and comparisons need for a review paper; this will make the paper more interesting.

If possible, you can express the solution suggestions for the problems you are trying to reveal through figures or implemented buildings.

 

Yours Sincerely

Reviewer 2 Report

Comments and Suggestions for Authors

The presented review paper by the authors has serious draw backs as listed out below:

1. It is neither well written or technically sound.

2. The degradation study is very limited and not described properly.

3. Being a review paper, the literature review is very short.

4. The capillary rise of the soluble salts is not clearly explained.

5. The abstract is short.

6. The presented paper lacks in novelty. 

7. The paper is not suitable for publication. 

Comments on the Quality of English Language

Moderate modification in English language is required. 

Reviewer 3 Report

Comments and Suggestions for Authors

I personally think that this article lacks both content and research depth.