Iowa State Historical Society Research Center – Centennial Building

The brick masonry clad building was in need of selective repointing and repairs on upper coursing beneath the roof parapet and patching and repair of limestone panels surrounding the windows. Additionally, the limestone cap over the main entry was leaking badly and in need of a long term solution. The final portion of the project was to address and correct drainage and masonry deterioration on the entry ramp and stair, which was a late addition and not original to the building.

An investigation of previous repairs revealed the source of the building masonry issues. A roof replacement project included new coping caps with insufficient extension to provide an adequate drip edge. The result was bulk water infiltration under the original cast cap. The limestone panel failure was traced to a detail that added sealant to the existing weep system and the base of the lintel over the windows, trapping moisture and leading to spalling at the top of the panels. The limestone panel roof over the entry relied on sealant joints which were a frequent maintenance issue.

To maintain the historic profile of the building, the decision was to repoint the upper tier of the building to ensure a continuous drain plane and prevent infiltration. The panels are addressed by cutting a slight slope at the head to ensure positive drainage and a capillary break to prevent freeze-thaw issues. Rather than replacing sealant, a new thru-wall flashing to membrane roof is installed over the limestone entry roof.

The entry ramp and stair received significant rework to correct cracking slabs and major mortar erosions. Demolition of the upper slabs revealed an open cavity below the entry retrofit with badly decayed metal decking formwork. Extensive backfill and a new sloped landing with integral drain stabilized the new walkways and diverts water away from vulnerable joints in the walls. New concrete includes fiber reinforcement for long term durability. The stone caps were removed all around and new cap flashing and drip edge is installed to eliminate water infiltration from above. This project was complete in 2019.

Client: State of Iowa DAS

Contractor: Bi-State Masonry