Old Senate Chamber Assessment Of Plaster Failure
Annapolis, MD: 2008
Assessment
The investigation of the 1772 Maryland State House's Old Senate Chamber was initiated by the failure of paint and plaster at several locations within the meeting room, especially in the corner to the right of the speaker's dais. This deterioration was a symptom of multiple causes, primarily condensation on the surface of the wall and from several sources at differing levels within the wall and, unlike previously thought, was not related to exterior rainwater penetration. Rather than address the root causes of moisture, past treatments focused on the visible symptoms, often using incompatible repair materials to cover up the damage.
In most of this chamber, plaster is applied directly on masonry. There is a corner steam chase built in behind the plaster directly behind the area of extensive failure by the speaker's desk. Warm air and moisture coming up through this chase from the steam generation area in the basement contributed to water in the wall.
Most of the walls in this chamber had been repeatedly patched. Many of these patches were delaminating. This meant that the failures were occurring at several layers, not just within a single layer. In some areas we believed calcimine or casein paint might have been an intermediate finish. Although quite durable paints, these often fail when over-coated by modern paints. We planned to use paint microscopy to help answer this question. Recent applications of low-permeability latex paints were trapping liquid water in the walls. Also the surface tension created when latex paint dries is often sufficient to split weaker layers of paint below. Moisture buildup under the latex was causing disintegration of the various water-soluble drywall mud, spackle, and gypsum plaster repairs.
Condensation of water - one of the least understood, most overlooked, and consistently misdiagnosed problems in historic buildings - is a major contributor to problems in this room. The HVAC system was inadequate to handle the moisture, particularly in this room right off the main entrance (an area of conflicting moisture and temperature extremes). In winter the exterior walls were cold and hidden from warming sunlight by overhanging trees, and subject to large amounts of water produced by the legislators through respiration and visitors entering with cold, wet clothing. Summertime tourists entering from the nearby exterior doors brought with them warm humid air into the air conditioned interior. Much of this water condensed where warm air met cold surfaces.
The exterior masonry had been thoroughly repointed with a hard, impermeable portland cement that further trapped water in the wall. There was also some evidence to suggest that the entire exterior might have been sealed up with a waterproofing treatment. Contrary to industry claims, the reduction of an evaporative exterior surface that is created by waterproofing increases water levels in porous masonry walls, often expressed through a host of problems on the interior.
The problem was multifaceted and each of the conditions we had identified were contributing. All would ultimately had to be addressed.