Analysis of the Factors Leading to the Degradation of Wooden Cultural Heritage Based on the Example of a 16th-Century Sacred Monument in Poland

Abstract

Microorganisms are one of the most critical factors involved in the degradation of buildings. Fungi that develop in historic spaces not only cause the degradation of monuments (immovable and movable) but can also negatively affect those who visit or use such spaces. This article is a case study of the 16th-century St. Catherine Church in Cięcina (Poland), whose walls became severely damp as a result of changes made to the church’s surroundings (relocation of the riverbed of the Cięcinka River, raising the level of St. Catherine Street and building a wooden fence on a concrete foundation around the church). The effect of the severe dampness of the building was the intensive development of Serpula lacrymans fungus and mold. This article highlights the importance of a multidisciplinary approach to hazard diagnosis in historic buildings.

1. Introduction

The primary goal of modern monument protection is to preserve the cultural landscape in its broadest sense. An integral part of the cultural landscape is the wooden architecture that has been co-creating it for centuries. Our landscape includes wooden mansions, inns, watermills, windmills, village cottages, and temples. Traditional buildings are important cultural heritage of any civilization, as they have historical, artistic, or scientific value worth preserving. These buildings often have a specific design characteristic of a particular region or country due to climatic conditions or the availability of building materials, among other factors. Unfortunately, the construction materials used to erect these buildings are exposed to several factors that affect their durability. In order to preserve these objects for future generations, special attention should be paid to developing appropriate ways to restore and preserve them [1,2].

The sustainability of wooden architecture, a form of the cultural-identity heritage of regions and societies, depends on many factors. Not infrequently, in many regions of the world, it is possible to find places or architectural objects that have been forgotten or neglected. The reason for this phenomenon can be seen in ongoing economic and social changes, as well as in globalization, which leads to the unification of urban spaces and the lack of promotion of knowledge of the cultural identity and history of regions. Leaving engineering structures, especially wooden ones, without proper maintenance often destroys them, resulting in the loss of the uniqueness of the regions. The old wooden buildings in Poland, with all their features, such as the type of construction, ornamentation and architectural details, etc., were created thanks to Poland’s immense abundance of forest land, and the preserved wooden architecture is considered valuable cultural and social heritage [1,2].

Wood used under proper thermal and moisture conditions is considered a durable material. However, when exposed to the variability of, for example, temperate climate atmospheric conditions, without proper maintenance, it is rapidly degraded by biotic and abiotic factors. It is, therefore, necessary to protect wooden buildings from, among other things, moisture, biological corrosion, and fire, as well as from the performance of renovation and modification works with new building materials [3]. The protection of wooden architectural monuments requires full recognition of the object—determination of the type of construction, materials used, forms of carpentry work, and especially thorough mycological surveys, which are a valuable source of information about the monument and which can significantly affect the preservation of its durability [4].

Fungi can destroy wooden cultural resources rapidly and dangerously. The most rapidly degrading and most common fungus capable of destroying residential and historic buildings in Poland is the fungus Serpula lacrymans [5]. It is believed that S. lacrymans, within six months of its developmental activity, can cause a dry weight loss of up to 70% of wood tissue. It is important to remember that the development of fungi on wood depends on the temperature and humidity conditions under which the wood is used, and it can be reduced by proper maintenance methods [6]. One of the methods and measures used to prevent the destruction and loss of our heritage is to monitor the state of preservation of historic buildings and the quality of their internal climate. An example is one of the oldest wooden monuments located in Poland. St. Catherine’s Church in Cięcina (Voivodship Silesian, Żywiec District, Węgierska Górka Commune; 49°36′55.75″ N 19°08′14.75″ E), in its oldest part, was erected in 1542 as a chapel. It was then expanded over several centuries (Figure 1) [7].

The Church of St. Catherine is an important regional landmark, one of the oldest surviving wooden churches in the Żywiec region. The church was entered in the Registry of Cultural Property [8,9].

Figure 1. Construction phases of St. Catherine Church in Cięcina based on dendrochronological research [10].

Figure 1. Construction phases of St. Catherine Church in Cięcina based on dendrochronological research [10].

2. Materials and Methods

2.1. Description of the Object

The church (Figure 2 and Figure 3) was built as a log structure. It consists of a short polygonal closed chancel and secondarily elongated nave, made in a pillar structure tower with starling, and surrounded by a closed arcade. In addition, on the north side, a sacristy was added to the chancel, and a small porch with a vestibule was added to the narrower part of the nave with a vestibule. Analogous, a slightly larger one was added on the south side, the rectangular Chapel of St. Francis of Assisi, preceded by a small porch. The central part of the body is covered with a gable roof, transitioning (over the chancel) into a multi-pitched roof; the tower is covered with a pyramidal cupola [6]. Research showed that fir (Abies alba) and spruce (Picea abies) wood was used in the construction of the church (

Table 1. Species of wood used in the construction of the church.

Parts of the Building	Fire Wood	Spruce Wood
Presbytery	Wall, roof
Nave (narrow part)	Wall, roof
Nave (wide part)	Wall, roof	Roof
Sacristy	Wall, roof	Wall
St. Francis chapel	Wall, roof
Tower	Structural timber	Structural timber

) [10].

An archival search did not reveal records of significant repair work on this building. At the same time, it cannot be ruled out that such renovation work took place, since the description of the dendrochronological research [9] includes the notation ‘for the time after 1893 falls the renovation of the northern wall of the first [author’s note: narrow part] of the nave’. This citation indicates that the wood sample taken from the lower part of the wall was dated to a later period than the samples taken from the higher zones of the wooden wall.

Among the more important works in the post-World War II period was the restoration of the church’s interior in 1949–1951. During the same period, the degraded lower beams of the walls were replaced. In the early 1960s (probably in 1962), efforts to secure the building continued, making a stone foundation for the crumbling exterior walls and reinforcing them with two brick pillars. The lower edge of the foundation was made at a depth of about 60 cm below ground level and, therefore, not according to the requirements of the ground frost depth in the area. In 1990–1992, several works were performed to improve the technical condition of the church. The structure’s foundations were strengthened by constructing a concrete band around the church with a depth of 120 cm and an upper width of ca. 40 cm, and the church area was drained [11].

An essential element in the history of the church, not directly related to work on the building itself, which has an impact on the current state of the building, was the relocation of the Cięcina riverbed from the northwestern part of the area around the church to the southeastern side. At that time, a dike was piled on the southeast side, separating the river from the church grounds, and a wooden fence on a concrete foundation was built around the church area, which blocked the natural outflow of rainwater (surface water) from the building. The second change around the church site that has damaged the church entailed raising the level of St. Catherine Street, which allowed rainwater to flow from the street under the church. Due to these changes in the terrain near the church, the foundation level of the studied building has changed in relation the surrounding terrain [11].

From August to November 2010, work was carried out, including reinforcing the roof truss, replacing the roof sheathing with shingles, and installing gutters and downpipes made of copper sheets. In June 2021, engineering work began on drainage around the church and drainage of the site. In the second half of 2021, storm sewers and a band drain were constructed. The project team also envisioned removing the existing concrete band around the church, and drainage water and water from the downpipes would be discharged through an intermediate well into an absorption well. However, these works still need to be completed. The drainage performed has reduced the formation of stagnant water in the zone of the lower parts of the church walls but has not solved the problem of high groundwater levels, which significantly affect the technical condition of the facility’s foundation zone.

2.2. Assessment of the Actual Technical Condition

As part of the assessment of the current state of preservation of the monument and the analysis of threats from biotic and abiotic factors, measurements were taken of the moisture content of the building materials, i.e., brick, plaster, structural wood, and room climate. The following were used to measure the moisture content of the building elements and microclimate: EXTECH M0290 (Flir System Inc., Nashua, NH, USA). In addition, during the visual inspection of the facility, three samples were taken from wooden structural elements. The moisture content of the wood was determined using the drying and weighting method. To measure the moisture content of the building elements and microclimate, the following were used: EXTECH M0290 (Flir System Inc., Nashua, NH, USA) and Trotec 660 (Trotec GmbH, Heinsberg, Germany). Due to the extremely valuable polychromes covering the walls of the temple, a full assessment of the technical condition of the supporting walls (wood degradation caused by the fungus S. lacrymans) was determined based on the wood moisture content, visual assessment of the deformation and cracking of the structural elements, supported by testing with a Bosch Digital Inspection Camera (Robert Bosh Power Tools GmbH, Stuttgart, Germany).

2.3. Assessment of Microbiological Air Pollution

In the nave of the church, four bioaerosol samples were collected using an AQUARIA Microflow α 90c device: sampling head with 380 conical holes ø 1 mm (Aquaria Srl, Lacchiarella, Italy). The operating parameters of the device during bio-aerosol sampling were as follows: airflow 100 L/min., exposure time 60 s, air sampling was performed at a height of 50 cm (2 bioaerosol samples) and 150 cm (2 bioaerosol samples) from the floor. Samples were kept in Petri dishes (90 mm) with maltose-agar medium (Biomaxima, Lublin, Poland). The samples were then incubated for seven days at 24–26 °C and c.a. 80% air humidity. Microscopy slides were made from the proliferated mold colonies. The morphological features of individual mycelial cultures were observed using a Nexcope NE620 light microscope (Delta Optical Sp. z o.o., Warsaw, Poland), using a 60× and 100× magnification, equipped with a Levenhuk M1000Plus camera (Levenhuk Poland Sp. z o. o., Warsaw, Poland).

The guidelines for the development of the research methodology were the provisions of ‘The Act on the Protection and Care of Historical Monuments’ [12] and good practices contained in documentation studies for immovable wooden historical monuments [13,14,15].

3. Results and Discussion

3.1. Main Defects and Damage Determined in the Church

In the 1990s, the concrete band around the building was covered with a textured plastic membrane. The way the film was laid has caused leaks between it and the foundation, allowing rainwater to penetrate deep into the concrete foundation (Figure 4). The membrane also blocks the evaporation of accumulated moisture. Concrete that becomes damp during rainfall retains moisture in its mass and slowly returns it to the church’s foundations. The band also creates a hardened zone around the building, resulting in additional moisture in the foundation wall from splash water. In addition, leaves pile up in the gutters and downspouts of the drainage system, obstructing the system. As a result, the lower parts of the church walls are flooded periodically with rainwater, which increases the degree of moisture in the foundation walls in these zones and creates favorable conditions for the development of biological agents.

During the visual inspection of the object, it was found that the horizontal insulation of the foundations was not continuous. Horizontal insulation was only present in those places where the lower zones of the nave walls had been repaired by replacing wooden elements damaged by S. lacrymans. Only in the chancel (the oldest part of the church) has the insulation been correctly installed so that it does its job. In other places, the insulation is missing or does not do its job.

The above-described condition of the building elements causes rainwater, and partly groundwater, to dampen the lower zones of the building walls. This creates favorable conditions for fungal growth in the church. Some of the walls show signs of biological corrosion caused by house rot fungi. This mainly applies to the zone over the building. The most severe fungal infestation of the walls is found in the south side porch (Figure 5, Figure 6 and Figure 7), the space behind the dismantled altar in the central area, and in part of the wall between the south side chapel and the nave (where the inspection opening was made), the walls under the choir. The degree of degradation of the wood is high enough to qualify these elements for replacement. In the southern section under the choir, the fungus S. lacrymans has also infected the wooden elements of the historic confessional (Figure 8).

If a building is heavily infested with S. lacrymans, the conventional method of wood treatment is recommended in Poland. This assumes the replacement of wooden elements inside which mycelium or mycelial cords of S. lacrymans were found. The wooden wall elements qualified for replacement were heavily colonized by S. lacrymans mycelia and showed transverse and longitudinal cracks, reducing the strength of the wood. Such strict adherence to the removal of wood infested and degraded by S. lacrymans is contrary to conservation doctrine, which seeks to maximize the preservation of historic substance in historic buildings. In this case, the main argument in favor of removing S. lacrymans-infested wood is that the species can survive in a dormant state for many years and transition to an active stage once conditions are favorable for development. In addition, the mycelium of S. lacrymans grows rapidly in buildings and quickly and severely degrades wood, causing brown rot, which is why it is considered one of the most dangerous house rot fungi.

3.2. Moisture Content of Wooden Walls and Air Humidity

Moisture tests have shown that the main dampness in the masonry structures of the foundations (moderately damp building foundations 5–8%) occurs in areas where the exterior walls are flooded by rainwater entering through leaks and the poor profiling of the church’s rainwater drainage system (nave: west wall, northwest wall, southwest wall; St. Anthony’s Chapel: southwest wall, northwest corner). The church floors were also damp due to unfavorable soil and water conditions and the lack of horizontal insulation of the subfloor layers. The remaining foundations of the church were not damp (<3%). The moisture content of the wood of the walls and the roof structure ranged from 9.6% to 17%, except for sites heavily infested by the S. lacrymans fungus, where the wood moisture content reached up to 47%. The temperature and humidity in the rooms on the day of the tests were as follows: nave—temperature: 14.8 °C and relative humidity: 50–52%, side porches of the entrance area—temperature: 15.4 °C and relative humidity: 56%, sacristy—temperature: 14.7 °C and relative humidity: 52%. The temperature outside the building was 14 °C, and the relative humidity was 52%.

3.3. Microbiological Air Pollution, Moisture Content of Wooden Walls and Air Humidity

Table 2. Assessment of the mold and bacterial contamination in the air—quantitative analysis.

Sampling Location	Molds * [cfu/m3]	Bacteria * [cfu/m3]	Impact I/O
			Molds	Bacteria
Nave—southwest corner	3230	140	3.98	0.77
Nave—southeast corner	2180	140	2.69	0.77
Nave—northeast corner	4390	210	5.42	1.67
Nave—northwest corner	3150	110	3.88	0.6
Ambient air (outside the church)	810	180	-	-

* Recommended permissible air pollution by mold and bacteria (total) in museum rooms—safe for humans: 2500 cfu/m³, and safe for collections: 150 cfu/m³.

shows the results of the quantitative studies, and

Table 3. Assessment of the mold contamination of the air—qualitative analysis.

Sampling Location	Tagged Mold Fungi
Nave—southwest corner	Penicillium sp. (BSL-1), Trichoderma viride * (BSL-1)
Nave—southeast corner	Acremonium sp. * (BSL-1 or 2), Mucor sp. (BSL-1), T. viride (BSL-1)
Nave—northeast corner	Cladosporium herbarum * (BSL-1), Penicillium sp. (BSL-1), T. viride (BSL-1)
Nave—northwest corner	Acremonium sp. (BSL-1 or 2), Mucor sp. (BSL-1), T. viride * (BSL-1 or 2)
Ambient air (outside the church)	Alternaria alternata (BSL-1), Aureobasidium sp. (BSL-1 or 2), C. herbarum * (BSL-1), Penicillium sp. (BSL-1)

* The most abundant species in the samples.

shows the results of the qualitative studies of the measurements of the microbial contamination of the air.

The amount of microorganisms found in the air was lower than the permissible air pollution in public buildings proposed by the Interdepartmental Commission for Maximum Admissible Concentrations and Intensities for Agents Harmful to Health in the Working Environment [16]. An auxiliary criterion for determining whether a building has a source of microbial contamination is the I/O (indoor/outdoor) factor [17]. I/O ratios between 1.5 and 2 indicate an indoor environment with normal conditions, while I/O ratios higher than 2 indicate inappropriate indoor environmental conditions, resulting in intense mold and/or bacterial growth in the tested room [18]. To calculate the above factor, it is assumed that the permissible ambient air pollution (outdoor) is 5000 cfu/m³ [19]. As a result of this study, the air in the nave of the church was found to contain mold many times higher than in the ambient air (I/O > 2). Among the molds found on the samples collected were allergenic and potentially pathogenic species. It is important to note that molds generally fall under the least dangerous category for humans, according to the biosafety level (BSL), which is a system that ranks the relative danger of various microorganisms.

The air microbiome is believed to significantly contribute to the deterioration of historical objects [20]. It is exciting to note that despite the severe dampness and degradation of the wooden walls caused by Serpula lacrymans, no intensive development of mold colonies was observed on the wall polychromes. Mold colonies were also not found on the temple furnishings, i.e., high and side altars, oil paintings on canvas, sculptures, confessionals, and people’s benches. However, numerous mold colonies were found on the surfaces of decorations that were deposited in the side rooms of the tower, where the ventilation and air circulation are severely restricted. In Poland, due to the lack of current legal and normative acts defining the threshold values for air pollution of residential, non-industrial premises, etc., the most commonly cited proposal is the Interdepartmental Commission for Maximum Admissible Concentrations and Intensities for Agents Harmful to Health in the Working Environment. It relates to the value of the permissible total concentration of fungi and bacteria in the air of residential, working, and public spaces at a certain level. According to the Expert Panel on Biological Agents’ proposal, the permissible concentration of mesophilic bacteria and mold in the air of residential and public spaces is 5000 cfu/m³. On the other hand, in archives, museums, museum warehouses, and historic preservation studios, the Expert Panel on Biological Agents recommends as safe for humans a microbiological contamination level of 2500 cfu/m³ (total fungi and bacteria), while a safe level for museum pieces is 150 cfu/m³ [21].

Among the mold species found were the strongly cellulolytic species Trichoderma viride, Cladosporium herbarum, and Alternaria alternata but also those whose food can be paint binders: Aureobasidium sp. and Penicillium sp. Molds can also colonize and damage the interior design of historic buildings. The changes caused by these microorganisms to paintings, polychromes and gilding on wood, etc., are related to their life processes and concern the following mechanisms: enzymatic activity related primarily to the processes of nutrition and respiration, the release of various metabolic products into the environment that are harmful to historic buildings, and the disfigurement and masking of surfaces [22]. Molds are also indicators of excessive humidity in buildings. In the case of temperate climates, such indicators are Alternaria alternata, Trichoderma viride, Acremonium sp. and Mucor sp. found in the nave of the church, developing at Rh > 90% Rh, as well as Cladosporium herbarum, Aureobasidium sp. developing at Rh 80–90% [23]. The numerous occurrences of these species may indicate that during periods when the church is unused, the relative humidity of the air may increase significantly.

An essential factor in maintaining the longevity of structures is knowing the environmental conditions under which fungal infestation can occur. During the inspection of the church, the observed dampness was caused primarily by the discontinuity of the horizontal damp proofing of the building walls, lack of vertical damp proofing of foundations, lack of moisture insulation of floors, poor soil and water conditions of the object’s foundation, capillary action of moisture from the ground through foundation walls, flooding of exterior walls by rainwater entering through leaks and poor profiling of the rainwater drainage system from the church building. Moreover, lack of adequate ventilation of the side porches of the entrance area and areas where the walls are duplicated and form an enclosed space (this applies to the walls at the junction of the side chapel, porch and nave on the south side) and the effect of rainwater (so-called splash water) on the exterior walls and foundations were also noted.

Morphological structures of the fungus S. lacrymans—considered to be one the most severe destructors of wood in buildings [24]—were found on the wooden structural elements and their interior located in the narrow and wide nave, the Chapel of St. Francis and its vestibule, and the porch under the tower (on the north and south sides).

The church has been in use for more than 480 years. It has been expanded over the years, with the last remodeling performed in 1932. After 1932, St. Catherine’s Church was no longer expanded; only ongoing renovation works took place, involving the replacement of damaged wooden elements, wall reinforcement, roof renovation, and site drainage.

Based on an analysis of archival photos from the early 20th century, it is clear how the environment around the site has changed over the past 100-plus years. Unfortunately, these changes were detrimental to the church, as they blocked the natural drainage of rainwater away from the building and exacerbated the degradation processes in essentially all the wooden elements in the ground zone. The renovation and modernization work performed removed the effects without eliminating the cause.

4. Conclusions

Caring for historical monuments is not easy. This is due to the variety of materials that previous generations used to make these objects and the many environmental factors that can cause damage to historic buildings [2,3]. Microorganisms that cause degradation of the historic substance can also affect the health of occupants of such historic buildings. Unfortunately, in the case of the appearance of moisture in the building and, at the same time, in the absence of symptoms of severe degradation of the building by Basidiomycota fungi, the problem of mold development in historic rooms may not be sufficiently recognized. This article describes the case of the 16th-century St. Catherine’s Church in Cięcina, which has been struggling with severe dampening of the building’s wooden walls and their degradation by the fungus S. lacrymans. Tests carried out in the summer of 2023 also drew attention to the high airborne microbiological contamination of the facility. Although mold is not classified as a significant factor in wood degradation (e.g., structural elements), it may pose a threat to decorations (e.g., polychromes, gilding, etc.) [25], and above all, it may pose a serious threat to public health in indoor environments (the faithful participating in liturgy, tourists, etc.) [26].

In summary, the identification of the etiological factors of the degradation of historic wood is a complex but indispensable field because it allows the adoption of a proper course of conservation proceedings. Accurate identification of the types and species of organisms that threaten historic buildings requires adequate biological preparation and specific research methods, both basic and advanced [27,28]. Conservation of monuments should use interdisciplinary artistic, technical, and biological knowledge, thus requiring a multidisciplinary approach. This relationship is particularly evident in the conservation, restoration, renovation, and reconstruction of historic wooden buildings [4]. Thus, to optimally select conservation methods, it is necessary to examine the object holistically, i.e., to identify all the bio- and abiotic hazards that may cause its degradation, determine the degree of degradation of materials, and then make recommendations based on the latest, yet already proven, trends in monument conservation. This approach to the conservation of a monument ensures that the right results are achieved through the principles of ethics and the requirements of conservation canons.