PRO Team Field Notes: Oakland’s Eastern Greenhouse Wall

by Charlie Paine
Preservation, Restoration, and Operations (PRO) Team Intern

Oakland Cemetery’s Beaumont Allen Greenhouse is located between the historic boiler room and carriage house structure near the cemetery’s northern boundary. These buildings were constructed around the turn of the 20th century and aided facility and lot management at Oakland as the cemetery continued to grow. The original greenhouse has since been removed, but the structure’s supporting walls remain. These walls may not support a greenhouse anymore, but they do support the cemetery’s historic integrity and serve as a symbol of our earliest efforts to make Oakland beautiful.

When a historic brick is covered in Portland cement, the moisture that was supposed to be absorbed and evaporated out, is retained in the wall.

The greenhouse walls were repaired several times in its history, but some repairs caused more issues to arise in the long term. In particular, the easternmost wall seems to have been partially rebuilt near the back top corner without proper bricking into the older wall for support. With parts of the wall not re-tied into the existing structure, the wall had little-to-no lateral support near the top. In addition to the poor re-structuring, the wall was capped, repointed, and in some places stucco’ed-over using Portland cement. Portland cement used as mortar and stucco can be dangerous for historic structures. Mortar is sacrificial and does its duty well only when it’s softer than the masonry it is binding. When a historic brick is covered in Portland cement, the moisture that was supposed to be absorbed and evaporated out, is retained in the wall. This is more degrading to historic bricks, which are more porous and less compressed than modern factory-made bricks.

Since the past repairs, the Beaumont Allen Greenhouse wall was retaining excessive amounts of water and allowed for many weak spots in the structure to develop and worsen to critical condition in recent months. The top of the wall had cracked, separated, and created a hazard for those walking near it.

Excessive amounts of water allowed for many weak spots in the wall.

This May a structural engineer with architectural firm Wiley|Wilson discussed with the PRO Team the Beaumont Allen Greenhouse’s east wall. The engineer addressed possible solutions to save the wall from collapsing. A feasible solution included: removing the cement cap atop the structure, repointing with an appropriate mortar, and inserting steel stitch rods into the wall to re-tie it.

Following the advice of the structural engineer, appropriate repairs have been made to the wall over the past two months, and the work is nearing completion.

Steel stitch rods were embedded every forth course of bricks to add stability to the structure.

Left: Reinforcing steel stitch beams are placed between every fourth row of brick. Right: the beams are supported with mortar.

The remains of the crumbling cement cap were chiseled off and are being recreated with a buff-colored lime mortar cap using the same mortar mixture the wall has been appropriately repointed with. With the wall’s repairs coming to an end, a final brace will be added in coming weeks to adjoin the wall to the carriage structure to ensure the wall’s longevity.

The wall after repairs.

Charlie Paine is a senior at College of Charleston, pursuing his bachelors in historic preservation and community planning and art and architectural history.