Thursday, August 11, 2011
Moisture Control at the Cole-Digges, Part II
While the Restoration Department was doing roof repairs at the Cole-Digges, the ever deligent headquarters staff pointed out two areas of interior plaster damage that could only have been caused by moisture. The common factors of the two areas were that they were both up high on the wall and they were both under a parapet wall. The top of the parapet walls at the Cole-Digges are about 7/8 wrapped in sheet rubber, which virtually eliminates the possibility of moisture penetration through the top. Examination of the outer faces of the upper brick courses revealed that the mortar in these upper courses had substantially failed, and had been like that during the 1995 restoration of the house. A good quality caulk had been used at that time to repair the mortar joints. This caulk was now at the end of its life. There were visible cracks where the caulk no longer adhesed to the brick. Removal of the caulk revealed that the vertical joints between the bricks were functional on the outside but void of mortar on the interior. So, rain would run into the caulked joints and down into the interior wall cavity via the vertical joints. Eventually this collected moisture would migrate to the two outer surfaces, doing no visible damage to the exterior of the wall, but damaging the plaster on the interior. The solution to this was to repoint the upper courses of brick and then repainting to match the building exterior. The wall cavities will be allowed to dry this summer, saving the plaster repair for the winter, or for when the diligent headquarters staff gets fed up with looking at it.