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Analysis of Moisture for the Preservation of Frescoes at Malpaga Castle Elisabetta Rosina Polytechnic ofMilano, Department of Conversation and History of the Architecture, V.Durando 38/a -20158 Milano,Italy e-mail :elisabetta.rosnia@polimi.it Guido Roche Architect, V.Tassis, 5-24129 Bergamo, Italy; e-mail :guido.roche@inwind.it Contact

ABSTRACT

The preservation planning of frescoes requires a precise knowledge about the building technique of the masonry, the microclimatic conditions inside the rooms, its variations due to the changes of the weather in addition to the measures of moisture and the map of its distribution. The case study presented in the paper regards the ancient castle of Malpaga, which is settled near Bergamo, Northern Italy. The building was begun in 14° century, and it was accomplished in 15° century by Bartolomeo Colleoni. Three layers of frescoes decorate the whole surfaces. Objectives of the analysis are the identification of the risk areas, because of the damage already visible and the microclimatic anomalous conditions, and the verification of the hypothesis about the causes of the moisture. Only NDT may be applied, because of the preciousness of the surfaces. The measures were repeated at different weather conditions and in the same days at different hours. The results revealed that the orientation, the disposition of the rooms, the number and wideness of the openings, contribute to modify the temperature of the air inside during the day, decreasing the threshold of dew in few hours and, above all, many times in a short period. The other measured variables are due to the differences of the thickness of the masonry and its component. The tests allowed to map the colder areas, where dew can condense, and the zones affected by rising damp. The results allowed to design the specific air-conditioning plan and those minimal interventions to decrease the effects of the air streams nearby the surfaces of the frescoes.
KEY WORDS:condensation, rising damp, ancient buildings, preservation, frescoes, NDT

1. FOREWORDS

1.1 Scenario
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[1]. 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"[2]. 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[3] , Donizetti Institute and Barnabò Palace[4], Castiglioni' Manor[5] , Cremona' Sant'Abbondio Church[6] ) 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. DATA RESEARCH FOR MOISTURE ANALYSIS AT 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[7], although the most ancient part of the castle can be dated back to the beginning of 14^th 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[10]. 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[11] 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 courtyard
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

3. THE ENQUIRES:PLANNING AND RESULTS

3.1 DESIGN
Objectives
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:

• Monitoring the microclimatic and environmental conditions, recording seasonal and daily variations, to determine anomalies and to project a new conditioning plant (psychrometrical analysis[12])
• Identification of the major risk areas (map of colder and damp areas by thermography, capacitive probes, Ground Penetrating Radar[13]), avoiding any collection of sample and destructive test
• Verification of the causes of water incoming

Hypothesis of water flows
Rising damp


1. Courtyard pavement

The descending pipes unloads rain on the porous stone pavements. The slopes of the pavement are inclined towards the center, where a tank collects the water. Here rain is collected and the water slacks. No pipes were found from the tank to the external moat.
2. Underground structures

In 1997 a break in the eastern wall of the moat allowed to discovery the foundation structure of the 15^th century fence, built by Colleoni. The rooms have no connection outside, and they keep high Relative Humidity and water content inside the masonry.
Condensation
The masonry very thick (60-80 cm), the lack of ventilation inside the rooms, the particular climatic condition (RH very high during all the year, cold temperature in winter, and at night in autumn and spring) are the preferable condition for condensation[14].

3.2 MEASURES
Microclimatic monitoring
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


The courtyard
In June and July the air temperature increases, because of the solar radiation, and consequently the RH decreases to its minimum. On the contrary in May and September RH reach the maximum: Specific Humidity (SH) has always high values. In this period the courtyard contains most stanching vapor, coming from the evaporation of the stone pavement, which causes different hygrometrical gradient nearby the walls (depending on their orientation).
Northern part
On the contrary, here the major climatic variations were recorded. In fact the openings have not frames, and the damp air masses come inside, travel across the rooms and entered the courtyard.
Eastern part
The exterior east side resulted the most dry in any beating. RH and SH values were always very similar and homogeneous (even though the lower value of RH was 70%). An increasing gradient was found towards the court side, up the maximum values (march).
Southern part
Solar irradiation incomes throughout the large windows and it affects the temperature inside the rooms and consequently RH distribution. In fact during the heating (during the first hours of the morning - east side, and late morning - west side) RH decreases, allowing evaporation from the damp surfaces. On the contrary during the air cooling (in the afternoon - evening) the excessive RH condenses on the colder surface (e.g. the glass of the windows but also the wall surfaces). These surfaces are under most risk of deterioration.
Western part
In this rooms the least variation were registered. Here the walls are thicker than the 15^th century's ones and there is only one opening for each room: that's why the climatic condition are maintained unchanged, without danger of condensation.

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.

Capacitivity Probes
The probes have been applied throughout the wall courtyard at 40, 140,180 cm from the ground.
Northern part
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).
Eastern Part
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.
Southern Part
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).
Western part
A maximum RH value is revealed nearby the northern portico (up to 75%).
On the southern side the average values are near 60%.

Anemometer measures
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.

Thermography
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[16], or using dependency of optical surface properties from moisture[17]. 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[18] (fig. 10a and b). In this zone the results of other NDT (GPR[12] 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

Condensation
Almost all the surfaces have a RH homogeneous distribution, both at the basis and in the upper part. Moreover, from the comparison between the measures taken in March and in February, some remarkable differences resulted, according to the environmental variation of RH and Temperature. In any case, the average value of RH of the surface is never below 55%, which is a high value indeed. The hypothesis that the court maintains the ambiental RH is confirmed, and easily condensation may occur in middle seasons, when the daily excursion are larger.
Rising damp
The rising damp was found only in some zones of the courtsides: Eastern-Northern corner of Romanino Portico, nearby and under the Eastern stair, in the Southern side. In these areas both thermography and capability probes data matches to find out a hygrometrical gradient decreasing with the elevation. The map of moisture affecting these areas resulted almost constant throughout all the seasons. Therefore the sources of damp should be localized: the results allow to discharge the hypothesis of a constant ground water but the leakages of descending pipes and the irregular absorption of the pavement could be responsible for spotted distribution of rising damp.

4. INTERVENTION PROJECT

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[19] 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

• Digging of a collecting interspace all around the perimeter of the court, to avoid the contact of the stanching water with the foundation of the masonry.
• Collection and elimination of the rain coming from the descending pipes by means of a new connection to the hydraulic plant of bathroom in the south side.

Intervention against condensation
HVCA

Fig 11: Project of localisation of the irradiant panels placed on the farement and air conditioning placed on the center of the room


HVCA system was supported by the analysis and designed according to the resulting indications (fig. 11): in the first areas the heating was designed to flow from the exhibition cabinet, located in the center of the rooms. In the physical mockup of a room, tracing gas allowed to verify the flow of air during the heating and to tailor precisely the system. In the second a very thin irradiating tiling was disposed on the original pavements. The HVCA system is completely removable. The system was based on these consideration:
• The thickness of the wall will contribute to maintain constant the microclimatic conditions, when the window frames of the openings are at their best condition. Consequently an accurate restoration of the frames will improve insulation. Wide glass surfaces (firstly in the eastern side) cause the thermal unbalance: a regulation of the conditioning system, room by room and hourly, will prevent it.
• Heating and ventilation only of the air inside the rooms: it is mandatory to avoid any air flux nearby the walls.
• The Temperature can range from 16°C to 18°C, 55-65% RH (according to the regulation[20]) throughout the year and all the day long.
• In the first area, used for passage and for exhibition paths, the visitors comfort will increased with a heating flowing very slowly.
• In the second area, where humidity is lower and no rising damp was found, the heating can reach 18-20°Cby means of irradiating panels.

Intervention against damage due to weather
Enclosures of loggias and Romanino Portico
The Northern portico is the most damage: unfortunately there are located the most precious frescoes, painted by Romanino in 1530.
• The enclosure of the portico side towards the courtyard should decreases the risk of damage because it prevents the flux of wet air from the courtyard and from the northern entrance tower.
• The thermal gradient due to seasonal condition is reduced.
• At the first floor the loggias are regularly moistened by spring rain; often even the walls are damp because of irregular thunder storm. In addition there are no descending pipes to allow the water flows down. Also in these cases the glass window may prevent any further weather aggression.

5. CONCLUSIONS

Crossing NDT it is possible to obtain enough information, even if qualitative, to determine the real distribution of humidity and to find out actual causes of the damages. The accurate analysis of the environment and of the microclimatic condition allows to plan the least destructive intervention, even in the case of and apparently serious rising damp. An economic advantage comes from the deep and extended analysis phase, because it is possible to tailor a most suitable intervention, improving the guarantee of certain results and reducing to the minimal impact with the building.

6. ACKNOWLEDGEMENT

The authors thank prof. Giuseppe Cruciani Fabozzi (Florence State University, Department of History of Architecture and Restoration of the structures) and all the people collaborating to the investigations

7. REFERENCES

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