1999 Conditions Assessment Survey of the Exterior Marble:
~~ Preliminary Observations & Analysis

	University of Pennsylvania graduate students survey and record conditions of exterior marble in 1999.

The interpretation of the exterior masonry conditions is critical as it ultimately determines a conservation strategy for the remedial and preventive conservation measures required. The complicated nature of the drawings with multiple layers of graphic conditions can be difficult to interpret in any meaningful context. It was recognized in the beginning of the planning of this project that the field survey process must be well developed. A variety of different methodologies are currently being used in architectural conservation to collect data for the conditions assessment of a historic site or structure. With advances in computing and imaging technologies, these methodologies tend to be fluid, and constantly evolving. Extreme attention must be paid to insure that the selected process delivers meaningful information for the established goals monitoring, treatment/repair, or cyclical maintenance.

Visual interpretation is always subjective. Members of the field team may record conditions slightly differently in severity and extent. Once recorded, the drawings are subject to variable interpretations depending on the graphic or spatial comfort acuities of the viewer. Where possible this survey has tried to balance subjective interpretation with objective data by creating clear, exclusive, descriptive conditions, free of causal implications. Better integration of a database with the survey drawings and analysis by means of disciplined calculations (like the surface square area chart below) provide a firmer foundation from which one can extrapolate more complicated deterioration cause and effect relationships.

A preliminary analysis of the drawings and the data given in the chart below allows the following observations to be made:

• The columns and the facades display different weathering patterns which appear to be a function of directional exposure, the variance in the stone composition, and the placement of the stone relative to its foliation planes.
  
• The location of a column appears to influence the rate of deterioration above any inherent deficiencies in the stone as indicated by the two central columns (4 and 5) having all of the lowest values of the calculated square areas except for one category, and having none of the highest values.
  
• None of the column drums could be definitively identified as having their foliation planes running horizontal (parallel to the ground); most foliation direction was indicated as being oblique (greater then 45 degrees) or nearly vertical.
  
• Column two has the highest square area of surface erosion of any column, which is occurring predominantly on the upper two drums.
  
• Column six is in the worst condition, having the highest amount of surface area loss from incipient spalls greater then ½", and dimensional loss, and the column also has the largest amount of exposed mineral inclusions (from which it could be inferred that these inclusions are the primary reason that large dimensionally unstable fragments have detached in such dramatic quantities).
  
• Some of the ashlar stones along the entablature and pediment show distinct deterioration patterns that follow "bookleaf patterns" across pairs of stones which were split from single blocks and laid side by side. Splitting a stone in this way can only be done with the foliation planes running parallel to the stone surface.
  
• The south sides of the columns (the protected faces) are consistently among the worst faces of each column. Is frequent water washing of the exposed marble faces more beneficial to the stone then a partially sheltered condition? What role, if any, did the coating have on the deterioration of the stone?

(It should be noted that contour scaling and surface erosion were so wide spread along the west elevation that there seemed to be little value in calculating its total square area. Mineral inclusions along the west elevation were drastically reduced in comparison with the amount of inclusions visible on the columns).

By recording the conditions as separate layers in AutoCAD®, querying the database, and quantifying conditions, deterioration patterns and trends can be studied and baseline conditions established. Future importation of the AutoCAD® data into ArcView® will allow greater potential for deterioration diagnostics and predictive modeling of areas of potential risk. Additional information and analysis was still in progress as this first report was being completed. Until the remaining elevations of the building have been surveyed only a portion of the information can be fully developed and integrated into treatment, repair and monitoring recommendations, (primarily the north portico).