Review of 'The influence of ground slab permeability on wall moisture in a historic building'

Level of importance

The publication is relevant for both the academic community and practitioners within the conservation industry working in historic buildings. It deals with the effect and consequences of the application of impermeable ground-bearing slabs on the floor of the interior of old buildings without a damp-proof course. This is an important topic because there is limited evidential data based on measurements to validate the hypothesis and belief among practitioners about the action and effect of capillary rise that may cause decay to the adjacent walls of the building. This case study shows that ground moisture would not necessarily be ‘driven’ up adjacent walls. However, models of the process may display different outcome results.

Providing accurate data based either on models, case studies, or laboratory work is critical to ensure the appropriate preservation of the structure and to avoid further decay.

This research work is based on a long-term case study which provides some interesting insights despite this it's a very specific case study with some missing information that may condition the representability of results. However, it represents a novel methodological approach and provides new findings in comparison to other publications in the field.

Level of validity

Overall, the hypothesis is clearly formulated but the argumentation is not very stringent. How damp and moisture may promote the decay of construction building materials and how it affects the health of occupants is not well justified. The data and results are interesting but the description of the building materials (e.g. limestone, sandstone ashlars? gypsum, lime or cement plaster?, painting layer, etc) and their petrophysical properties, are specific to this case study but these were not well described nor measured and hence maybe not statistically significant.

The interpretation of results is also unsound, and a better discussion of results is missing to draw a solid conclusion. By contrast, the methodology is described with an exhaustive level of detail that wouldn’t have been necessary unless the focus of the research is based on this. Nevertheless, some important useful methods applied in this research are not clearly described (e.g. explanation on how the impermeable layer was installed and fitted (sealed) onto the ground; how the collected samples for gravimetry analyses were preserved to avoid dehydration until analyses were performed in the lab; the identification for the location of the drills to introduce the timber dowels and deep wall probes, etc.). More onsite and/or laboratory measurements (from collected samples) would be very supportive to validate the research findings.

More specifically, there are some issues that would benefit from an improvement or clarification:

1. From the title of this article ‘The influence of ground slab permeability on wall moisture in a historic building’ the reader expects to have more accurate and representative results to establish that influence’. However, the paper deals mostly with the methodology used to establish this in a very particular case in which the type of building materials and underlying ground where the building is settled is very specific to this study. Different outcomes could have been obtained for other types of materials where the physical properties should be known either by measurements or at least by references.

2. As mentioned above, the final hydric, capillary, and evaporation behavior, water transport, and mechanisms of decay of building materials that could happen or not or being more or less severe, will be conditioned, among other factors by the local climate and weather and type of petrophysical properties of building materials and soil/ground/rocks where they're settled. More information of materials’ properties obtained from measurements or at least references would be important to better discussion and conclusions from results; e.g. Type and main physical properties of the buildings materials and soil/ground of this historic building? Are these frequently used in the UK, England, other countries? Are the type of soil and location-ground settlement representative of many historic buildings in the UK, other countries? In this case study, it seems that the ground underneath the building is clay soil (mixed with 'fill'?? this term should be clarified) which is mostly impermeable; the influence of this for example should have also been discussed. There should be references providing generic petrophysical characteristics of the sandstone rock geological formation underneath that would be relevant and important to mention and discuss here (eg. open porosity, capillarity rates, etc). Also regarding the building materials; are the stone ashlars of the building also sandstone?

Additionally, a discussion about the climate and the weather during the monitoring period would have been relevant e.g the discussion on evaporating drying is missing a link/references to climate/historic weather conditions of this particular UK region and future implications (also for other climates/regions in other countries); discussion the orientation of the building, seasonally rainfall? predominant rain/ wind direction? etc.

Some info about the Physico-chemical properties and context of the building structure, location, and weather would provide a more consistent and realistic interpretation of results.

3. The discussion about why meter readings were erratic and did not show a temporal trend in contrast to gravimetric analyses that is mentioned at the end of the Results section should be better discussed and moved to the corresponding Discussion of Results section.

4. Regarding the following statement posed in the abstract and conclusions: ‘moisture content within the wall did not increase following the installation of a vapour-proof barrier above the floor. This indicates that the moisture levels in the rubble wall were not driven by capillary rise.’ :  

There are no consistent results and neither a thoughtful interpretation of these to assure this. Several questions should be important to address and discuss, such as: ‘where is the moisture coming from’? Why the moisture content measured from the timber dowels is there if the source is not capillary rise?’ Why is there more moisture content at the base of the wall compared to higher height? This and other arguments would enrich the content of the manuscript and the quality of the research. Some clarifications would be useful to avoid some contradictory interpretation of results

Level of completeness

The authors reference appropriate international scientific publications and provide relevant information to follow their findings.

However, more references are missing to discuss these findings and obtained results, such as the influence of physical parameters related to the hydric behaviour of the different building materials and adjacent/subjacent soil/ground of this particular case study; the influence of climate/weather; the correlation/discussion between measuring and modeling data and the obtained results is unsubstantial and the volume of the latest scientific and technical references or publications to argument the hypothesis is scarce and not enough to draw the main stated conclusion.

More specifically, some other issues to clarify:

1. The second paragraph of the Introduction section that describes the hypothesis and related physical factors involved should be better deliberated. The factors that might influence the occurrence or severity of rising damp in the walls that may happen due to a lack of damp proof course and the installation of impermeable ground bearing slab installed in a historic building during renovation and how this may alter the moisture dynamic of the building should be better addressed. Despite the limited evidence-based on long-term monitoring, the authors mention that there are references to this phenomenon. The provision of those ‘technical and product literature’ references would be useful.

2. Among other factors, such as climate, weather, or geological features, rising damp will depend on the type and petrophysical properties of surrounding materials, i.e. of both the soil (ground) and building materials (walls) which will condition the capillary forces mentioned by the authors. The influence of their physical properties, such as open porosity, pore size distribution, tortuosity, capillarity coefficient, etc. should be mentioned and discussed. This is important since the final consequences (including rising damp) may be very different depending on the type of materials and hence on the type and kinetics of water transport and the eventual mechanisms of decay (e.g. freezing-thaw, salt crystallisation, etc).

3. Even though in the ‘Methods’ section (which should be better named as ‘Materials and Methods’), it was already explained in the Level of Validity query,  that the methodology is thoroughly described but some important information is still missing, such as the description of installation of impermeable layer, etc. (see these comments above).

Level of comprehensibility

The language is clear and easy to understand for an academic. The article is overall systematically and logically well structured. However, the description of some parts of each section is not clearly organised and the reader wonders about the principal and main content that should be indicated at the beginning of each section rather than suddenly being explained at the end.

More specifically, there are some minor issues to consider improvement or clarification:

1. In the last paragraph of the Introduction section, the term ‘conductivity properties’ may be confusing; consider using the term 'hydric properties' or physical properties of building materials that influence ‘water transport’. Additionally, specify the type of ‘monitoring’ (e.g. monitoring moisture content?).

2. In the ‘Methods’ section (second paragraph) briefly specify what type of ‘instruments’? e.g. data loggers? sensors? The ‘Instrumentation’ subsection should be specified that the moisture meters are not directly measuring 'moisture' when inserted through the building materials of the wall; these are moisture equivalent measurements WME (%) using electric resistance mode (pin mode).

3. The figure captions are properly described but the quality of some images and pictures (e.g. Fig. 1 and Fig.2) is not good enough or relevant to provide the necessary information (e.g. image of the external view of the building is missing; Fig.2. is blurry and building materials cannot easily being distinguished, etc.).

Overall Impression

Very interesting paper and relevant topic. However, the argumentation to describe the hypothesis and relevance of the study is unsubstantial. The description of this specific ground site, soil and type, and physical properties of construction and building materials is poor. A thoughtful interpretation of data and discussion of results is also missing. More references and other cases studies of these and other building materials, soil/ground and climates/weather, and better discussion of the findings would provide more solid conclusions.