·Table of Contents
·Conservation and Restoration in Art and Architecture
Analysis of Moisture for the Preservation of Frescoes at Malpaga CastleElisabetta Rosina
Polytechnic ofMilano, Department of Conversation and History of the Architecture, V.Durando 38/a -20158 Milano,Italy e-mail :firstname.lastname@example.org
Architect, V.Tassis, 5-24129 Bergamo, Italy;
The presence of damp in ancient masonry is often related to the building technique and to the physical characteristics of the employed materials. It depends on the bonding of the masonry and the lack of effective devices to prevent water incoming. The components of ancient walls are porous and they absorb high water quantities (both vapor or liquid); the poros capability of providing routes permitting a sufficiently free movement of gas and liquid allows the water to cross the wall, and eventually to evaporate throughout the surface. The damage appears on the surfaces, affecting large areas, both precious (decorated by mural, frescoes, and stucco) and ordinary; at the visual analysis it is rather difficult to determine the thickness of the damaged layer, which could be few mm or till 8-10 cm depth. The economical evaluation of the preservation project depends largely on the intervention to apply on the surfaces, and a underestimation of serious damages is a frequent risk. Water content in walls is a fundamental information regarding the decay analysis in cold climatic condition; usually water content is a key factor when temperature stays below zero for several months. In those cases the water volume grows as frost and generates pressure within porous of the wall materials, therefore generating cracks in the structure. In North Europe and North America, the temperature stays below zero for long period during winter: in addition to the damage already described the water in the insulation material coating causes thermal bridge the building. In temperate climatic area damage is concentrated on the surface (few cm depth), related to the water transition between the wall and the surrounding environment and the characteristics of absorption of the materials. In addition to water content, the other boundary conditions play a main role in decay process: "The anomalies of water content in masonry are not definitively known: the water content is more related to the evaporative speed of the materials than to their absorption capability". Weather monitoring and microclimatic analysis are request to estimate the actual state of the masonry and for the design of the optimal preservation boundary condition.
1.2 The role of design in the preservation from damp damages
The study cases (Gessate and Corsico Churches , Donizetti Institute and Barnabò Palace, Castiglioni' Manor , Cremona' Sant'Abbondio Church ) show that damp rising is a chronic and recurrent condition of the ancient buildings, and it is a long life defect. Public and private buildings, built for important customers too, are submitted at the same fortune. Nevertheless, the presence of water in the lower level of building did not prevent their use, even for the noble uses. Surely the cellars were not used for reception, and in ground floor only few rooms were open to guests. Rising damp becomes a crucial problem when the affected rooms are employed for usage not compatible with high humidity range (for instance living or storage of corruptible stuff, etc.) or when the boundary conditions changed (increase of the road level and consequent change of the slopes nearby the building, leakage of drainage pipes, increase of the ground water level). A correct design cannot avoid to take into account the environmental and microclimatic conditions. Comfort of the users should compromise with optimal preservation condition of the buildings. Moreover the refurbishment costs sharply increase to obtain (and maintain) radical changes of humidity ratio. An attempt for a more conscious design is shown in the following case of Malpaga castle.
2.1 HISTORICAL OVERVIEW
The Malpaga Castle (fig. 1-2), located in northern Italy, near Bergamo, is mentioned for the first time in documents of 1395, although the most ancient part of the castle can be dated back to the beginning of 14th Century. Initially, until Colleoni's works after 1456, the castle was composed by: a single wall fence, a main tower, a boundary wall and an external moat[8,9]. Historical documents report that an internal artesian well (actually present in the courtyard) allowed the soldiers to resist the enemy siege for long period. In fact, despite of the nearby presence of the Serio river, no superficial ground water was in the surrounding area. When Colleoni, as retired captain of the "Serenissima" Republic of Venice, restored the castle from 1456 to 1487 as it his main residence, he accomplished the digging of irrigation channels in the countryside. In fact the ground has thick rubble layers which drains the rain water preventing any regular agricultural activities. Moreover Historical document report that Colleoni built the external fence onto the previous moat. The foundation of the new part were built as vaulted rooms, filled with moisten earth. After Colleoni's death in 1487 the castle became the country residence of his inherits. After the half of 1700's it became a warehouse for corn crops; and before 1743 the frescoes were whitewashed to allow more protection for corn crops. In fact only since 1948 some pieces of the frescoes have been discovered and restored; the same applied to the decoration that dated initially 1300 at ground and first floors.
|Fig 1: Malpaga castle: western side||Fig 2: Malpaga castle: main entrance, southern side|
2.2 ANALYSIS OF SURFACES: MATERIALS AND DECAY DUE TO DAMP
The four elevations of the courtyard are similar for materials but they are different in the decay levels because of the orientation.The masonry is made of rubble and ashlers, lime mortar and three layers of frescos are the exterior finishing.
The Northern side shows a homogeneous damage of the surface, caused by weather: chromatic alterations are diffused on the painting, now turned in a oxidated thin crust and, toward west, there are some lacks. The clay stone columns ("Pietra della Luna", from a local quarry) have few black crusts and many lacks, due to mechanical bumps rather than frozen cycles. The portico masonry is more damaged in the lower part, where delamination of plaster and deep lacks are frequent.
The Eastern side has many more lacks of the plaster and some pieces are substitued with cement mortar. Salt deposits and diffused erosions are evident on the columns surfaces.
In the Southern side (fig. 4-5) the major damage is at the base of the wall, where the lacks of plaster are more extended than on the other sides. Mould and salt deposits are concentrated, and the refurbished pieces of plaster show that here damp rising has been working for a long time. In the southern portico the base of the wall is damaged with delamination and stains of the plaster, decreasing with the highness.
The main damage of Western side is due to rain falling and mechanical bumps: lacks of plaster and chromatic alterations are diffused in the lower part of the wall.
The pavement is composed by sand stone, and a fence of bricks is settle around the ashlars. Erosion of the stone surface cancelled the traces of the ancient finishing. Moulds and moss are distributed between the ashlars, above all in collection points of rain (in the center of the courtyard). The bricks are damaged too, with cracks and diffused erosion. Moreover the analysis of materials employed and of their state of damages, a geometrical survey of the hydraulic plants had been performed.
|Fig 4: Malpaga castle:Southern courtside Survey of the materials.||Fig 5: Malpaga castle:Southern courtside Survey of the damages|
The accurate survey of the castle and the surrounding areas pointed out the critical nodes, object of the enquires. The courtyard resulted the crucial point: preliminary analysis had been planned to study the microclimatic variation, to discover the path of the incoming water and to detect the pipes permitting the water to flow out.
Therefore objectives of the investigations are:
Hypothesis of water flows
Several beatings were performed across 1998 to record even the least differences due to environmental variation and anomalies inside the building. Among them spring-summer measures have been more effective to evaluate the influence of daily excursion and sun influence. In the investigated areas (whole ground floor) resulted very high values of RH (always major than 65%) for all the beatings 1996-1997 (fig. 7, 8, 9). On the base of the results it was possible to articulate the castle in some systems, affecting each other.
|Fig 6: Malpaga castle, ground and first floor: plants of the future usage||Fig 7: Map of Temperature °C, June 1998, ground floor||Fig 8: Map of Relative Humidity %, June 1998, ground floor||Fig 9: Map of Specific Humidity gr/mc, June 1998, ground floor|
Measures of humidity and Temperature of the surfaces
Capacitivity and dielectric probes were used to survey the temperature and humidity of the surfaces. The results of the capacitivity probes were more accurate and precise, while the dielectric probes could be applied only where the surfaces were not frescoed (or already damaged). The air temperature was 6-8°C and RH ranged 80-84% during the test.
The probes have been applied throughout the wall courtyard at 40, 140,180 cm from the ground.
In the portico, Romanino's frescoes are the most damp, the average value is higher than 65%, with two maxima: 75% (on the eastern side) and 77% (on the western side).
Average values range 65%, homogeneously. Under the stairs there is a zone at higher RH on the surfaces and in the air. In the rooms the wall perpendicular to the courtside have RH decreasing from the courtyard to the external elevation. May be that in these walls humidity flows from the courtyard towards the moat.
Very high values (up to 75% near the artesian well, in the south-western room and the bathroom). Inside the bathroom RH and Specific Humidity have very high values, too. Because of the lack of ventilation, condensation may occurs when the air temperature drops.
The surface temperature decrease from the external elevation to the courtside (that never gets sunlight).
A maximum RH value is revealed nearby the northern portico (up to 75%).
On the southern side the average values are near 60%.
The anemometer were located in the courtyard, nearby the walls, the openings, and in center of the court.
Speed and direction of winds and draught were recorded during the spring 1997, in February-March surveys. It resulted that the peculiar geometry of the building generates two well identified draughts, coming from south and north across the entrance towers. The southern stream joins the air coming from the cellars and from the stairs connecting the first floor loggia. This air licks the walls, causing the diffused erosion of the frescoes. A cold draught coming from the northern entrance tower generates almost a Venturi's effect. High speed draught licks the masonry, determines evaporation and causes the diffused damage. Moreover the flux of cold air coming from the North affects the microclimate inside the rooms, decreasing the temperature.
The use of thermography for the moisture monitoring of buildings is well documented in the literature [3,4,15]. Active or passive techniques have been used, based on the changing of thermal parameters, or using dependency of optical surface properties from moisture. Both the approach were used at Malpaga castle and the whole surfaces of courtsides were investigated. Generally the damp areas where settled at the basis of the walls; the high of the moistened surfaces is variable. The highest level of the damp areas resulted in Northern side of Romanino Portico, at the corner with eastern side (fig. 10a and b). In this zone the results of other NDT (GPR and capacivity probes) confirmed the presence of high water content. A second damp area was found on the southern side, under the windows of the bathroom. The map of humidity showed a narrow band up to 20-30 cm from the ground. Thermography was used to detect delamination of plaster, the bond of the masonry beneath the parget, and the presence of infilled openings (the results are not reported here).
|Fig 10: Thermography of the western side of the northern tower. Rising damp is detected as colder area (Fig.10a) and the visual state (Fig10b)Air temperature 23°C, RH 52%, September 1997, Agema 489LW|
3.3 DISCUSSION OF THE RESULTS
From the investigation the condensation resulted as the main cause of humidity, and, to a lesser degree, the localized rising damp (fig. 3).
|Fig 3: Map of the results of the investigations|
4.1 FUTURE USAGE OF MALPAGA CASTLE
Any restoration is fails in a short time when the building is not submitted to the most respectful use and a regular maintenance program; in the Malpaga case the preciousness of the castle is that it was preserved almost unchanged for the last six centuries. Therefore is a critical decision the choice of the use requiring the least modification and improving the preservation condition. A possible new use of the whole complex, the castle and the surrounding village, is the extension of the Accademia Carrara Exhibitions to a suburban location. The actual state of conservation of the castle is seriously taken in account, as a basilar information which allowed to tailor the most suitable use, room by room. Depending on the causes of moisture, and consequently the intervention to apply, two different zones were obtained: in the first, where rising damp and evaporation affect the walls, the microclimatic condition will be maintained constant, low temperature (never below 12°C, nor higher than 18°C) and controlled RH. In the second, where high Humidity value are due to condensation, a balancing heating and an air conditioning system were studied, to avoid drop in temperature or unbalanced heating. Also, the use of the ground floor rooms will be different: the first zone will be a passage; instead in the second, the constant heating allows the people to remain, to work, to read, to consult archive, etc. According to this subdivision, a double exhibition path will be settled in the first area (fig. 6). Instead the offices, the bathrooms, the services (a cafeteria, the archives, the library) will be located in the second area, more comfortable and warmer. At the first floor the microclimatic conditions radically change, allowing a traditional heating.
4.2 TECHNICAL INTERVENTION FOR THE PRESERVATION OF FRESCOES
Intervention against rising damp
Collection of rain
Intervention against condensation
|Fig 11: Project of localisation of the irradiant panels placed on the farement and air conditioning placed on the center of the room|
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