Submit to this Journal Review for this Journal Propose a Special Issue

Article Menu

Share Help Cite Discuss in SciProfiles

Open AccessArticle

Peer-Review Record

Influence of Surface Sanding on the Coating Durability of Spruce as Facade Board

Coatings 2025, 15(10), 1133; https://doi.org/10.3390/coatings15101133

by Ondrej Dvořák^1,*

, Monika Sarvašová Kvietková^1,*

, Petr Horák¹

, Markéta Kalábová¹

, Chia-Feng Lin²

, Dennis Jones^1,2,3

and Petr Ptáček⁴

Reviewer 1:

Marko Petrič

Reviewer 2: Anonymous

Reviewer 3:

Cornelia Baera

Reviewer 4: Anonymous

Coatings 2025, 15(10), 1133; https://doi.org/10.3390/coatings15101133

Submission received: 27 August 2025 / Revised: 20 September 2025 / Accepted: 23 September 2025 / Published: 1 October 2025

(This article belongs to the Special Issue Recent Advances in Surface Functionalisation, 2nd Edition)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Terminology: Please in the whole paper change the terms “water-based” and “solvent-based” into “waterborne” and “solventborne”. The suggested terms are more frequently used and by my opinion more appropriate.

Line 51: I do not understand well what was intended with this expression “To compound matters”. Maybe write this sentence in a more understandable way.

Lines 100-102: “A key parameter in sanding is the abrasive grain size and is usually expressed as the number of grains per unit area (e.g., per 1 cm²).” I have not read what is written in the cited reference No. 26, but this is definitely not right. Grain size (also called grit size) refers to the average diameter of abrasive particles used in sandpaper, typically defined by the number of mesh openings per inch through which the grains can pass — higher numbers indicate finer grains. But the number of grains per unit area is most often called grit coating type (closed coat, open coat, semi-open coat) and can be called also abrasive grain density or abrasive grit distribution. Please correct!

Introduction and elsewhere in the paper: Please define the knowledge gaps in the field covered by your paper more precisely and clearly desxribe, how your paper addresses these knowledge gaps and what is novel/new in your paper appart from what has already been published.

Line 143: The standard EN 927-3 should be cited with the reference No. 30 and not 29.

Figure 2: The letters showing the length of the bar (related to magnification are only hardly visible, or better to say, they cannot be read.

Line 245: “probably because their rougher surface texture allowed more coating absorption.” Is this just your assumption (based on what – please provide some supporting references), or the result of your measurements. It would be great if you could measure penetration of your coatings into the substrates (and or film thicknesses – better penetration, thinner films) and present and comment the results of such measurements.

Subtitle “Hygroscopicity changes«: in this section you do not write about hygroscopicity, but rather about contact angles i.e. wettability. So it would be better to use “Wettability changes” or “Hydrophobicity changes” or even “Hydrophilicity changes”, or “Water repellence changes”

Lines 295-296: It is written “For water-based paint coating samples, contact angle decreased during the first three months of exposure (Fig. 5b)”, but in Figure 5b, contact angles on solventborne coated samples are shown !??

Lines 305-313: Here you talk about “water evaporation”. But it is not clear about which water evaporation, when, in which phase, do you talk about. Please provide a brief explanation.

Lines 314-315: It is written “For the solvent-based coating, contact angle decreased almost linearly during the first nine months, from 100° to approximately 50° (Fig. 5a).”, but I guess in Figure 5a there are contact angles on uncoated surfaces shown ?? And why this has to be repeated (see Lines 295-304).

Line 329: “probably due to the use of thin-film coating systems” – as I have written this somewhere before, it would most welcome (or even necessary to provide data on dry film thicknesses).

Line 342: “In the case of higher roughness, the coatings penetrated 342 the surface more deeply” See my previous comment(s) about this issue.

Line 375: “sanding with grit sizes P40–P80 increases the retention of coating systems”. Did you measure it?

Author Response

Dear Reviewer,

I would like to sincerely thank you for your time, careful reading, and constructive comments on our manuscript. Your feedback is very valuable and will help us improve the quality and clarity of our work.

Thank you for your suggestion. We have replaced all instances of “water-based” with “waterborne” and “solvent-based” with “solventborne” throughout the manuscript, as recommended.

Line 51: I do not understand well what was intended with this expression “To compound matters”. Maybe write this sentence in a more understandable way.

Thank you for your comment. We have rephrased the sentence for clarity.

Thank you for your valuable comment. We have corrected the statement.

We thank the reviewer for this valuable comment. In the revised version of the manuscript, we have emphasized the novelty of our work more clearly.

Line 143: The standard EN 927-3 should be cited with the reference No. 30 and not 29.

Thank you for pointing this out. We have corrected the citation, and EN 927-3 is now referenced as No. 30 instead of 29.

Figure 2: The letters showing the length of the bar (related to magnification are only hardly visible, or better to say, they cannot be read.

Thank you for your comment. We have modified the figure so that the scale bar text is now clearly legible.

Thank you for your comment. The statement was based on a hypothesis that rougher surface textures may lead to increased coating absorption. We recognize the need for experimental validation and plan to measure coating penetration and/or film thickness.

Subtitle “Hygroscopicity changes«: in this section you do not write about hygroscopicity, but rather about contact angles i.e. wettability. So it would be better to use “Wettability changes” or “Hydrophobicity changes” or even “Hydrophilicity changes”, or “Water repellence changes”

Thank you for your suggestion. We have changed the subtitle from “Hygroscopicity changes” to “Wettability changes” to more accurately reflect the content of this section.

Thank you for noticing, it was a typo. We have corrected it.

Lines 305-313: Here you talk about “water evaporation”. But it is not clear about which water evaporation, when, in which phase, do you talk about. Please provide a brief explanation.

Thank you for your comment. We have clarified the text to specify that the “water evaporation” refers to the loss of moisture from the wood substrate during natural weathering, which occurs continuously throughout the exposure period. This evaporation affects the coating–substrate interaction and can influence surface properties such as roughness and contact angle. The explanation has been added to the revised manuscript.

Thank you for noticing, it was a typo. We have corrected it.

Line 329: “probably due to the use of thin-film coating systems” – as I have written this somewhere before, it would most welcome (or even necessary to provide data on dry film thicknesses).

Thank you for your comment. As mentioned above, we plan to address this part in a follow-up study. It is a comprehensive issue that deserves its own study. We would also like to connect it with the gradual dusting of the surface over time.

Line 342: “In the case of higher roughness, the coatings penetrated 342 the surface more deeply” See my previous comment(s) about this issue.

See our previous comment. Thank you.

Line 375: “sanding with grit sizes P40–P80 increases the retention of coating systems”. Did you measure it?

was measured in table 7 according to EN ISO 2409

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The topic of this paper is appropriate for the journal. This is without a doubt a very interesting manuscript, it has many qualities. However, I believe it has some problems. My suggestions are listed below:

INTRODUCTIONS:

The novelty is not well highlighted in your paper. You can highlight the novelty of your research compared to previous research studies.

METHOD:

Line 116: Could you please provide the exact location, including the altitude? Do you have detailed information about the samples used, such as their age, diameter, and other characteristics?
Figure 1: Please explain the difference between green and blue zones.
Line 129: Please change “For” to be “for”
Line 130: Did the coating used have any color or transparent? If yes, please add it.
Did you measure the viscosity of your coating? Or do you have information regarding the viscosity of your paint from the manufacturer?
Line 134: Could you explain in detail for drying time according to manufacturer’s procedure? Did you perform sanding between coating layers to avoid an uneven surface after coating?
Did you determine the spreading rate of each coating?
Line 136: The uncoated sample were coated by silicon coating in front side. Did you do coating in the edge side for untreated or treated wood to prevent swelling or distortion also?
Table 1: Did you have comprehensive information regarding the seasonal climate conditions during the measurement period?
Line 153: Did the color measurements take at the same point at 3 months, 6 months, and so on...
Did you measure the wettability of your coatings (water and solvent based coating)?
Line 183: What is the peeling angle used when testing paint adhesion?
Line 198: How did you measure the surface roughness? Did you measure all the surface or some points?
Could you explain the parameters of profilometer, for example the diamond tip radius, tracing length, the cut off, and speed of the tip.

RESULT:

In general, you have explained your results. However, the explanation of the results in this chapter is very brief. There is no justification about why the result happened or what it has attributed to other results. It is possible that the authors can explain scientifically more clearly in this chapter.
Figure 3-5: Please explain the abbreviation of SM-F-R, SM-120-R, etc. You could explain in the methodology section and after you could use and homogenize
Figure 3: I agree that rough surfaces can absorb more coating material and therefore provide better protection during exposure. On the milled surface wood sample coated with solvent coating, why did it have the highest color change value? If you look at it, the milled surface has the roughest value.
Line 297-298: If you mentioned that microcracks and surface irregularities occurred after 6 months of exposure, it can be said that the surface became rougher. However, why did the contact angle increase after 6 months? A rough surface will decrease the contact angle value. Do you have any other arguments?
Figure 6: As I mentioned before about surface roughness measurements. The image you presented, is it only at one measurement point? If you did it at several points, could you show the average value of Ra?

Author Response

Dear Reviewer,

INTRODUCTIONS:

The novelty is not well highlighted in your paper. You can highlight the novelty of your research compared to previous research studies.

We thank the reviewer for this valuable comment. In the revised version of the manuscript, we have emphasized the novelty of our work more clearly.

METHOD:

Line 116: Could you please provide the exact location, including the altitude? Do you have detailed information about the samples used, such as their age, diameter, and other characteristics?

We thank the reviewer for this helpful comment. The Norway spruce (Picea abies (L.) Karst.) used in this study originated from the University Forest Enterprise in Kostelec nad Černými lesy (Central Bohemia, Czech Republic) at an altitude of approximately 391 m above sea level. The wood was free of knots and cracks. Unfortunately, we do not have more detailed information regarding the age or growth characteristics of the trees, as these data were not recorded at the time of sampling.

Figure 1: Please explain the difference between green and blue zones.

Thank you for your comment. In the figures, the green color has been used to indicate measurements performed with the spectrophotometer, and the blue color indicates measurements performed with the glossmeter.

Line 129: Please change “For” to be “for”

Thank you for your suggestion. I have made the change from “For” to “for” as recommended.

Line 130: Did the coating used have any color or transparent? If yes, please add it.

Thank you for your comment. The coatings used semi-trenasparet.

Did you measure the viscosity of your coating? Or do you have information regarding the viscosity of your paint from the manufacturer?

Viscosity measurements were not part of this study.

Line 134: Could you explain in detail for drying time according to manufacturer’s procedure? Did you perform sanding between coating layers to avoid an uneven surface after coating?

Thank you for your comment. The drying time between layers followed the manufacturers’ procedures:

ADLER Pullex PLUS-LASUR Pigmented) – drying time: [from technical data sheet, 12 h at 23 °C and 50% RH].

DColor FK 47 UV PROTECT Pigmented) – drying time: [from technical data sheet, 4 h at 20 °C and 65% RH].

According to the manufacturers’ recommendations, no intermediate sanding between layers was required, and therefore it was not performed in our study. Moreover, it could distort the results.

Did you determine the spreading rate of each coating?

Thank you for your comment. Yes, the spreading rate of each coating was determined according to the manufacturers’ technical data sheets:

ADLER Pullex PLUS-LASUR Pigmented) – spreading rate: 8–12 m²/L.

DColor FK 47 UV PROTECT Pigmented) – spreading rate: 9–12 m²/L.

Line 136: The uncoated sample were coated by silicon coating in front side. Did you do coating in the edge side for untreated or treated wood to prevent swelling or distortion also?

Thank you for your comment. The uncoated samples were treated with a silicone coating only on the front side, as stated. The edges of both untreated and treated wood were not additionally coated, in order to simulate realistic exposure conditions and allow evaluation of dimensional stability and coating performance under natural weathering.

Table 1: Did you have comprehensive information regarding the seasonal climate conditions during the measurement period?

Thank you for your comment. Yes, we had comprehensive information regarding the seasonal climate conditions during the measurement period. Natural weathering was conducted at the Prague-Suchdol site (50°07'49.68"N; 14°22'13.87"E, 285 m altitude) for 12 months, from June 2023 to July 2024.

Line 153: Did the color measurements take at the same point at 3 months, 6 months, and so on...

Thank you for your comment. Evaluations were carried out at five intervals: 0 months (before exposure), 3 months, 6 months, 9 months, and 12 months. The color measurements were taken at the same predefined points on each sample at every interval to ensure consistency and comparability of the results.

Did you measure the wettability of your coatings (water and solvent based coating)?

Thank you for your comment. We have adjusted the subsection title in line with your suggestion and also based on the recommendation of the second reviewer. Originally, it was labeled as “Hydrophobicity Measurement”, but in the revised manuscript it is now presented as “Wettability changes” to more accurately reflect the content.

Line 183: What is the peeling angle used when testing paint adhesion?

Thank you for your comment. Paint adhesion was evaluated according to ČSN EN ISO 2409, which specifies the cross-cut test method.

Line 198: How did you measure the surface roughness? Did you measure all the surface or some points?

Surface roughness of the wood samples was determined using a Talysurf Intra 2 profilometer (Leicester, UK). Measurements were carried out at five predefined points on each sample to ensure representative results. The arithmetic average roughness (Ra) was calculated from these points. The instrument was set with the following parameters: diamond tip radius 2 µm, tip angle 90°, tracing length 4.8 mm, cut-off 0.8 mm, and tip speed 0.5 mm/s. Mean Ra values with standard deviations are reported to represent the surface characteristics of each sample. We include this.

Could you explain the parameters of profilometer, for example the diamond tip radius, tracing length, the cut off, and speed of the tip.

Thank you for your comment. We have now included detailed specifications of the profilometer in the manuscript. Surface roughness was measured using a Talysurf Intra 2 (Leicester, UK) equipped with a wide range gauge. The instrument settings were as follows:

Range / Resolution:32 mm stylus: 32 mm / 125 nm (1.26 in / 4.8 μin)

Reach: 50 mm
Shank clearance: 5.3 mm
Tip radius: 2 µm
Tip angle: 90°
Minimum bore: 10 mm

These parameters have been added to the Materials and Methods section to ensure reproducibility of the measurements.

RESULT:

In general, you have explained your results. However, the explanation of the results in this chapter is very brief. There is no justification about why the result happened or what it has attributed to other results. It is possible that the authors can explain scientifically more clearly in this chapter.

We added the names of samples to the text

Figure 3-5: Please explain the abbreviation of SM-F-R, SM-120-R, etc. You could explain in the methodology section and after you could use and homogenize

Thank you for your comment. We have added explanations of the sample codes in the Materials and Methods section. For example:

SM F – R – spruce wood - reference

SM-120-R - spruce wood - P120-sanded - reference

SM-80-R - spruce wood – P80-sanded - reference

SM-40-R - spruce wood – P40-sanded - reference

SM F – 1 - spruce wood – reference - solventborne coating

SM-120-1 - spruce wood - P120-sanded - solventborne coating

SM-80-1 - spruce wood – P80-sanded - solventborne coating

SM-40-1 - spruce wood – P40-sanded - solventborne coating

SM F – 1 - spruce wood – reference - waterborne coating

SM-120-1 - spruce wood - P120-sanded - waterborne coating

SM-80-1 - spruce wood – P80-sanded - waterborne coating

SM-40-1 - spruce wood – P40-sanded - waterborne coating

Afterwards, these abbreviations are used consistently throughout the manuscript.

Figure 3: I agree that rough surfaces can absorb more coating material and therefore provide better protection during exposure. On the milled surface wood sample coated with solvent coating, why did it have the highest color change value? If you look at it, the milled surface has the roughest value.

If we look closely at the scale of the roughness graph, we can notice that the values show that the milled surface had the lowest roughness.

Line 297-298: If you mentioned that microcracks and surface irregularities occurred after 6 months of exposure, it can be said that the surface became rougher. However, why did the contact angle increase after 6 months? A rough surface will decrease the contact angle value. Do you have any other arguments?

Thank you for your comment. Although surface roughness generally tends to decrease the contact angle, the observed increase after 6 months may be due to surface chemical changes, such as partial leaching of hydrophilic components or the formation of a thin hydrophobic layer on the coating surface caused by UV exposure. These chemical modifications can outweigh the effect of increased roughness, resulting in a higher contact angle. We have added this explanation to the revised Results and Discussion section.

Figure 6: As I mentioned before about surface roughness measurements. The image you presented, is it only at one measurement point? If you did it at several points, could you show the average value of Ra?

Thank you for your comment. The surface roughness measurements were performed at multiple predefined points on each sample. We used the mean value of the results.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Please refer to the PDF below.

Comments for author File: Comments.pdf

Author Response

Hello,

Thank you very much for your comment. In combination with other commenters, we have edited the text and we believe that thanks to your cooperation it has been raised to the level of the manuscript. We believe that the edited text is of sufficient quality.

We appreciate your time and look forward to future cooperation.

Have a nice day

Authors

Reviewer 4 Report

Comments and Suggestions for Authors

Manuscript Title: Influence of surface sanding on the coating durability of spruce as facade board

This manuscript presents an experimental study on the influence of different surface preparation methods (milling and sanding with P40, P80, P120 grits) on the durability of two common coating systems (solvent-based and water-based) on spruce wood during 12 months of natural weathering. The authors assessed surface degradation through key indicators such as color change, gloss, contact angle (hydrophobicity), adhesion, and surface morphology inspection.

Overall, this is a well-designed study with high practical significance that fits well within the scope of the journal Coatings. The results provide valuable information for the wood processing and coatings industries, particularly in optimizing surface treatment processes to extend the service life of exterior wood products. The research methodology employs standard and reliable methods. However, the manuscript requires minor revisions to key aspects of data presentation, analysis, and structure to achieve the highest quality before publication.

Some comments:

Table 1 effectively summarizes the climatic exposure conditions. Given the established role of UV radiation in initiating photo-degradation in similar coating systems, a more detailed evaluation of its specific impact on the studied materials would significantly strengthen the manuscript. Could the authors elaborate on whether the observed degradation patterns (e.g., chalking, cracking, gloss loss) are consistent with UV-driven mechanisms?
The 'Recommendation' section contains valuable insights that would be more effectively positioned within the standard structure of a scientific manuscript. Integrating these points into the 'Discussion' section to interpret the findings, and/or distilling them into key takeaways for the 'Conclusion', would enhance the paper's academic flow and impact.
Exposure Duration: The exact duration of the experiment needs clarification. The methodology section states "from June 2023 to July 2024," which is 13 months, but the title and other parts of the text refer to a 12-month period.
Figure/Table Captions: Captions should be self-explanatory. For example, in the captions for Figures 3, 4, and 5, it should be clarified that "SM-F-R" stands for "Milled surface - Reference," "SM-120-1" for "Sanded P120 - Solvent-based coating," etc., so readers do not have to refer back to the methods section. The title for Figure 6 could be more specific about the research subject.

Author Response

We would like to sincerely thank the reviewer for their careful reading of our manuscript and for the constructive comments and suggestions provided. Your detailed feedback has helped us to clarify ambiguous points, improve the structure, and strengthen the scientific discussion of our results. We highly appreciate the time and effort you have dedicated to reviewing our work.

Table 1 effectively summarizes the climatic exposure conditions. Given the established role of UV radiation in initiating photo-degradation in similar coating systems, a more detailed evaluation of its specific impact on the studied materials would significantly strengthen the manuscript. Could the authors elaborate on whether the observed degradation patterns (e.g., chalking, cracking, gloss loss) are consistent with UV-driven mechanisms?

Thank you for this valuable suggestion. We have expanded the discussion to address the role of UV radiation in the observed degradation. The patterns we recorded—gloss loss, the onset of micro-cracking (after ~6 months), and incipient chalking—are consistent with UV-driven mechanisms reported for similar systems. In brief:

Binder photodegradation (chain scission and oxidation in alkyds; side-chain scission/oxidation in acrylics) reduces surface cohesion, promoting chalking as pigment/filler particles become exposed.

Embrittlement of the coating matrix increases susceptibility to micro-cracking, which we observed alongside surface irregularities in later intervals.

UV-induced micro-roughening (together with particulate deposition) diminishes specular reflection, explaining the progressive gloss loss.

On rougher, milled surfaces, locally thinner films and enhanced light scattering likely intensified these UV effects, which aligns with the larger appearance changes noted for those specimens.

We have added a concise paragraph in the Results and Discussion linking these mechanisms to our findings and clarifying that the trends are consistent with UV-initiated photo-degradation under the south-facing, 45° natural-weathering setup.

The 'Recommendation' section contains valuable insights that would be more effectively positioned within the standard structure of a scientific manuscript. Integrating these points into the 'Discussion' section to interpret the findings, and/or distilling them into key takeaways for the 'Conclusion', would enhance the paper's academic flow and impact.

Thank you for this constructive comment. We agree that the current placement of the ‘Recommendation’ section is not fully consistent with the structure of a scientific manuscript. In the revised version, we have integrated these points into the ‘Discussion’ section, where they serve to interpret our results in the broader scientific and practical context. This restructuring ensures a smoother academic flow and strengthens the overall impact of the paper.

Exposure Duration: The exact duration of the experiment needs clarification. The methodology section states "from June 2023 to July 2024," which is 13 months, but the title and other parts of the text refer to a 12-month period.

Thank you for pointing this out. We acknowledge the inconsistency regarding the exposure duration. The experiment was conducted from June 2023 to June 2024, corresponding to a 12-month exposure period. The wording in the methodology section has been corrected to ensure consistency across the manuscript.

Figure/Table Captions: Captions should be self-explanatory. For example, in the captions for Figures 3, 4, and 5, it should be clarified that "SM-F-R" stands for "Milled surface - Reference," "SM-120-1" for "Sanded P120 - Solvent-based coating," etc., so readers do not have to refer back to the methods section. The title for Figure 6 could be more specific about the research subject.

Thank you for this helpful suggestion. We have revised the figure and table captions to make them fully self-explanatory, so that readers do not need to refer back to the methodology section to understand abbreviations.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

In general, the paper is better, and you satisfactorily performed the proposed changes or answered to my questions. However, I think some minor issues are still to be arranged.

If I saw right, the following matters were not solved, although you are saying that it was corrected (see below). Maybe I read wrongly, but please check, and correct, if necessary:

It is written “For water-based paint coating samples, contact angle decreased during the first three months of exposure (Fig. 5b)”, but in Figure 5b, contact angles on solventborne coated samples are shown !?? Thank you for noticing, it was a typo. We have corrected it.

It is written “For the solvent-based coating, contact angle decreased almost linearly during the first nine months, from 100° to approximately 50° (Fig. 5a).”, but I guess in Figure 5a there are contact angles on uncoated surfaces shown ?? And why this has to be repeated (see Lines 295-304). Thank you for noticing, it was a typo. We have corrected it.

Author Response

Hello,

a colleague has gone through everything and it should be fixed.

Have a nice day

Authors.

Reviewer 2 Report

Comments and Suggestions for Authors

I have accepted the manuscript revisions. The manuscript is now ready for publication.

Author Response

Thank you!

Reviewer 3 Report

Comments and Suggestions for Authors

Recommendation: Major Revise

Most of the suggestions of initial Review Report were not solved; I recommend the authors to carefully check those remarks and solve them as asked!

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Information included in the review report.

Author Response

Comments: 1. The title is clear, specific, and relevant, effectively conveying the main focus of the research, namely investigation on how different sanding treatments (P40, P80, P120, and milling) affect the performance of two types of coatings (solvent-based and water-based) under natural weathering.

The considered keywords accurately reflect the scope and focus of the study and would help researchers find this paper when searching for related topics.

Abstract: the abstract of the paper is pertinent, but there are a few areas where it could be improved for clarity, structure, and impact.
- Strengths: It clearly states the topic — the effect of surface pretreatment on coating durability of spruce wood under natural weathering, mentioning the types of surface treatments and coatings (solvent-based and water-based), also the applied methodology (briefly outlining the evaluation techniques — color change, gloss, contact angle, and visual inspection); it also emphasizes the key findings and also the conclusions, namely the importance of surface pretreatment and coating type for long-term performance.
- Suggestions to Improve the Abstract:
  - Use of shorter sentences might improve readability;
  - The mentions “temporary increase in contact angle” and “rapid decrease in wettability” are recommended to be more clearly linked to the coating types and their implications;
  - Addition of some quantitative information and specific data points (e.g., ΔE values, contact angle ranges) could make the findings more concrete, even from this starting point of the paper.
  - Solve the vague phrases like “probably due to” — instead, use “suggesting that” or “indicating.”, which alter the credibility of the study.

Response: Thank you very much for these constructive remarks. We have also revised vague wording such as “probably due to”. In the revised manuscript, these expressions have been replaced with more precise formulations such as “suggesting that” or “indicating”, in line with your recommendation. This adjustment improves both the credibility and the clarity of the study.

Comments 2:

Introduction: the Introduction of the paper is clear and pertinent, but there are a few areas where it should be improved for clarity, structure, and impact.
- Strengths: The introduction is pertinent, presenting both the topic and the authors’ approach, and it sets the stage for the study’s relevance and methodology. It introduces to the paper’s topic, which is interesting, addressing a practical issue in wood construction and It is also convincing, due to literature review presenting prior research and shows a clear experimental design. Moderate by novelty, as sanding and coating have been studied, the combination of natural weathering, multiple grit sizes, and two coating systems on spruce facade boards adds specificity and applied value.
- Suggestions to Improve the Introduction: The authors are asked to clarify the research gap more explicitly: E.g., “While many studies have examined artificial weathering, few have assessed the combined effects of sanding and coating under natural ” The authors are requested to elaborate and extend the research overview, with more specific details:

“While many studies on wood weathering have been conducted under controlled laboratory conditions [27, 28, 29], investigating natural weathering conditions provide valuable data for developing service life prediction models and optimising protective systems for real world applications.” – please elaborate the actual aim and results of these studies; supplementary, for a better context identification, the authors are requested to identify potential studies of outdoor exposure studies for wooden surfaces, applied methodologies and extend the meaning of their findings aligned to a potential methodological pattern.

Response: Thank you for this valuable suggestion. We have revised the Introduction to more clearly emphasize the research gap and to explicitly state the aim of our work. The revised text now highlights that, while many studies have addressed artificial weathering, only limited research has focused on the combined effects of sanding and coating systems under natural outdoor exposure. Our study aims to address this gap by evaluating the influence of surface preparation and coating type on the durability of spruce wood during 12 months of natural weathering.

Material and methodology: the Material and Methodology chapter complies with the research scope, is convincing and proper, but there are a few areas where it could be improved.

Strengths:
- Complying with the Scope (outdoor exposure experimentally assessing how different surface pretreatment methods—specifically milling and sanding with different grain sizes—affect the effectiveness of protective coatings on spruce wood during natural weathering:
It clearly defines the relevant variables: surface treatments (milling, P40, P80, P120), coating types (solvent-based and water-based), and exposure conditions.
It uses standardized procedures: EN 927-3 for sample preparation and weathering, ISO standards for gloss and adhesion.
It covers relevant performance metrics: color change (ΔE), gloss, hydrophobicity (contact angle), adhesion, roughness, and visual/microscopic evaluation.
It includes natural weathering, namely 12-month exposure at a real outdoor site, which adds practical, valuable relevance.
- Methodology chapter is convincing and proper (outdoor exposure experimentally assessing how different surface pretreatment methods—specifically milling and sanding with different grain sizes—affect the effectiveness of protective coatings on spruce wood during natural weathering:
Comprehensive Testing: Multiple physical and chemical properties are evaluated, giving a holistic view of coating performance.
Replicability: Sample sizes and replication are considered adequate; conditioning and measurement protocols are clearly described.
Use of Standards: Reliance on EN and ISO standards ensures methodological
Real Applicability Relevance: Natural weathering over 12 months provides insights beyond artificial lab tests; the longevity of exposer increases the study value
Statistical Analysis: Duncan’s multiple range test is used to validate differences between
Remarks for improving the Material and methodology chapter:
A brief description of the actual experimental methodology, apart from specifying the used technology and equipment, should be provided for all mentioned tests: Color measurement, Gloss measurement, etc. Specification of the standard governing the testing methodology is not considered enough, generating confusion and lacks of understanding by non-experts but interested in the current study; also only a limited number of readers might have access to the specified norms and standards.
Hydrophobicity Measurement - the authors are asked to be more specific testing methodology;
Graphical information or relevant pictures related to the experimental approach (specimen preparation, specific equipment, actual measurement performing, etc) could improve the chapter and increase the attractiveness of the study, also bridging the gap for non-experts. A step-by-step visual workflow: From raw wood to final testing might be also helpful.

Response: Thank you for your valuable suggestions regarding the Materials and Methods section. We have revised the manuscript to provide experimental procedures

Results and discussion: The Results and Discussion chapter of the paper generally complies well with the scope of the study, which is to assess how different surface pretreatment methods (milling and

sanding with various grit sizes) affect the durability and performance of protective coatings on spruce wood under natural weathering conditions.

Strengths:
Clear Alignment with Objectives: The chapter systematically addresses all the parameters outlined in the methodology: color change, gloss, contact angle (hydrophobicity), adhesion, and It compares uncoated, water-based coated, and solvent-based coated samples across different surface treatments.
Use of Visual and Quantitative Data: Tables and figures (e.g., Figures 3–6) support the findings with visual and numerical evidence and the discussion connects observed trends to known mechanisms (e.g., UV-induced lignin degradation, microbial colonization).
Scientific Reasoning: The authors explain phenomena like gloss increase due to photobleaching and contact angle changes due to dust clogging, proving an in-depth understanding of wood surface chemistry, which leads to valuable data and data analysing, and therefore, well-founded
- Weaknesses and Improving Remarks:
Overly Technical Language Without Clarification: Some terms (e.g., chromophoric carbonyl groups, sessile drop method) are not sufficient explained, which may lead to reduced accessibility to the study understanding.
Inconsistent Depth of Analysis:
- While color and gloss changes are well-discussed, adhesion results are briefly mentioned and lack deeper interpretation.
- The statistical variability in gloss and contact angle measurements is noted but not fully
Limited Integration Across Parameters
The chapter treats each parameter separately. A more integrated discussion could link how roughness affects both gloss and hydrophobicity, or how coating absorption influences multiple
Missing Visuals of Microscopic Findings
- The text references microscopic contamination and surface degradation, but only one image (Figure 2) is provided. More visuals from microscopy would strengthen the
Ambiguity in Some Conclusions: Statements like “the development were consistent across surface treatments” (page 10/16, row 316-317) are vague and grammatically incorrect. It’s unclear what “development” refers to, please rephrase.
General Suggestions for Improvement:
- Addition of summary tables comparing performance across treatment are
- Inclusion of more microscopic images to support claims about surface degradation are considered beneficial.
- Necessity to clarify statistical significance where variability is
- Improving transitions between sections could improve enhancing

Response: Thank you for your comment. We have clarified technical terms and revised the text to provide a clearer and more accessible explanation of the concepts, aiming to improve understanding for both expert and non-expert readers. Thank you for the suggestion regarding summary tables. We decided not to include additional tables because the results are already clearly presented in the figures. Adding tables would largely duplicate the graphical data without providing new information. All key values, trends, and differences between surface treatments, are fully visible and interpretable from the existing figures. Thank you for your suggestion regarding additional microscopic images. Unfortunately, we do not have further microscopy data beyond those already included in the manuscript.

Conclusion: The Conclusion chapter of the paper is generally convincing and appropriate, and it complies well with the scope of the study. It effectively summarizes the findings and offers practical recommendations based on the experimental results. However, there are a few areas where clarity, structure, and impact could be improved.

Strengths:
Clear Summary of Findings, as it reiterates the main outcomes: that both surface pretreatment and coating type significantly affect wood durability under natural It highlights the

differences between rough and smooth surfaces in terms of gloss, hydrophobicity, and degradation rate.

The Practical Recommendations section provides actionable advice for selecting surface treatments and coatings based on environmental conditions and aesthetic priorities; it suggests recoating intervals and maintenance strategies, which are useful for practitioners.
Consistency with Scope and Objectives: The conclusion ties back to the study’s aim: evaluating how sanding and milling influence coating performance on spruce wood.
- Weaknesses and Improving Remarks:
Language and clarity: Some sentences are long and could be simplified for better
- Example: “Rougher-finished surfaces showed lower initial gloss values, but better long- term stability of the contact angle and a slower overall degradation rate…” (Pag 13/16, row 366-368)
Structure and flow: The Recommendation section is valuable but could be formatted more clearly, perhaps as bullet points or subheadings. The transition between the conclusion and recommendation is abrupt; a short bridging sentence would help.
Lack of quantitative recap - The conclusion could benefit from briefly restating key quantitative findings (e.g., ΔE values, gloss loss percentages, contact angle ranges) for impact reinforcing – only suggestion, not mandatory.
Limited discussion/specification of study limitations: The chapter does not mention any limitations of the study (e.g., manual coating application variability, single geographic location, exposure duration); Including this would strengthen the credibility and transparency of the research.
No mention of future perspective - A brief note on potential future research directions (e.g., testing other wood species, longer exposure periods, or different coating formulations) is expected in most scientific studies.
General Suggestions for Improvement:
- Addition of summary tables comparing performance across treatment are
- Inclusion of more microscopic images to support claims about surface degradation are considered beneficial.
- Necessity to clarify statistical significance where variability is
- Improving transitions between sections could improve enhancing

Response: Thank you for the comment. We have revised the manuscript to simplify long sentences and improve readability, while keeping the scientific meaning intact. Based on the recommendation of another reviewer, the Recommendation points have been moved to the Results section, where they are better integrated with the presented data. In the Conclusion, we avoided repeating results that have already been summarized in the Results and Discussion sections.

The language and warding: minor The paper uses technical and academic language suitable for a scholarly audience; no major spelling errors were found. Still, some adjustments are recommended to be performed, where the case:
- Awkward or imprecise phrasing: “Figure Marking of measurement zones on the sample.” – page 3 of 16, row 127 – rephrase.
- Inconsistent or Incorrect Word Usage: ”The development were consistent across surface treatments.” – page 10/16, row 316;
- Punctuation Issues: Missing commas in compound sentences;
- Spelling and Typographical Errors
  - Minor typos like “wet film thickness was 60 µm. The first set (n=12) was coated…” (– page 3/16, row 129-130) — missing punctuation or spacing.
  - Occasional incorrect pluralization or agreement (e.g., “coating systems… is therefore more suitable…” - page 3/16, row 129-130, should be “are therefore more suitable…”)
- Awkward or Redundant Sentences
  - Some sentences are overly long or contain redundant
  - Example: “This degradation, initiated by UV radiation, leads to the decomposition of aromatic structures of lignin, resulting in optical lightening of the surface.” (– page 10/16, row 316) — could be simplified for clarity.

Examples of Awkward or Confusing Sentences

“The short-term increase in gloss can be attributed to the initial phase of photochemical degradation of lignin in the surface layers of the wood.” – page 10/16, row 259-260;
- Suggestion: “Gloss increased initially due to early photochemical degradation of lignin in the wood’s surface layers.”
“Although the trends were similar across surface pretreatments, rougher surfaces generally retained higher contact angles in the later stages – possibly because they absorbed more paint, improving long-term protection.” – page 10/16, row 300-304;
- This sentence is clear but could be split for
“The application of coating systems, both water-based and solvent-based, provided a noticeable protective effect, with differences between the surface treatments reflected primarily in the rate and extent of degradation across measured parameters.” – page 10/16, row 363-365;

Suggestion: Break into two sentences for clarity:“Both water-based and solvent-based coatings provided noticeable protection. Differences in surface treatments mainly affected the rate and extent of degradation.”

Response: Thank you for your valuable comments. The suggested revisions and clarifications have been incorporated into the manuscript.

General remarks:
- Standardization of test standard references (notation):

European Standard EN 927-118 3 [30] – page 3 of 16, row 118-119 - reference is provided;

- EN 927-3 [29] – page 4 of 16, row 143;

ČSN EN ISO 180 4624– page 5 of 16, row 180; - no reference is provided;
ČSN EN ISO 2409 [34] [table 3]:– page 5 of 16, row 180; - reference is provided; Note: Checking of the whole text is required.

Response: Thank you very much for your detailed observation regarding the standardization of test standard references. We carefully revised the entire manuscript and corrected the inconsistencies.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

General recommendations:

Most of the suggestions of initial Review Report were solved in a satisfactory (but not excellent manner); a complete overview of the paper is recommended before publishing, for avoiding technical language flows, ambiguity and even small language errors.

Ambiguity in Some Conclusions: Statements like “the development were consistent across surface treatments” (page 12/18, row 388-389) are vague and grammatically incorrect. It’s unclear what “development” refers to, the rephrasing was recommended, but it was not performed.
Standardization of test standard references (notation), meaning it would be preferred to choose using only the European name of the standard, (EN 927-118 3) or the national particularization of it (ČSN EN ISO 180 4624), not both of them.
etc.

Author Response

Dear Reviewer,

We would like to thank you for your careful evaluation of our manuscript and for your valuable comments. Your suggestions helped us identify areas where clarity and consistency of the text needed improvement. Below, we provide our responses to the main points:

Ambiguity in some conclusions

We agree that the original formulation, such as “the development was consistent across coating types,” could be vague and grammatically inaccurate. The text has been revised to make it clear that it refers to the monitoring of changes in gloss and color across different coating types, and that these changes exhibited similar trends throughout the testing period.

Standardization of references to test standards

In accordance with your recommendation, all references to standards have been presented in a consistent format. The manuscript now includes both variants – the European standard designation (EN/EN ISO) and its national counterpart (ČSN EN/ČSN EN ISO) – with each reference clearly identifying the corresponding standard.

Language and stylistic review

The text has undergone a thorough linguistic and stylistic revision to eliminate minor language errors, ambiguities, and technical inconsistencies. A careful proofreading has been carried out to ensure the manuscript is clear, fluent, and understandable for the reader.

We believe that these revisions have significantly improved the quality of the manuscript and addressed the ambiguities noted in your review.

Thank you for your constructive comments and for the time you dedicated to evaluating our article.

Sincerely,

Authors

Article Menu

Influence of Surface Sanding on the Coating Durability of Spruce as Facade Board

Further Information

Guidelines

MDPI Initiatives

Follow MDPI