Poured Concrete Problem-Solving on an Iconic 1960s NYC Skyscraper
Cathedral Stone Products provided custom solutions including products, education, and inspection related to the restoration of this iconic skyscraper.
Built in 1966, this poured concrete New York City Landmark required significant renovation by 2019
In 1966, the 31-story I.M. Pei-designed residential structure at 505 LaGuardia Place was heralded for its Brutalist contemporary architecture and innovative poured concrete construction. But by the early 21st century, the New York City Landmark needed more than just a face lift.
Restoration got off to a rocky start when mockups using another company’s Product failed to cure. During inspection and sounding, all four patches installed had failed to adhere properly—even inside a specially constructed heated rooftop shed.
It was then that Accardo Engineering brought in Cathedral Stone Products. We did another series of mockups with our M90 Concrete Repair Mortar. We worked in similar conditions, but without a surrounding shed or heating apparatus. Our M90 patches cured and passed the sounding test.
With that goal met, we moved on to another challenge: getting a color match close enough to be approved by New York City Landmarks standards. An authentic match required that aggregate be embedded into the surface of each patch—consistent with I.M. Pei’s original specifications. That meant determining how to embed the M90 patching material with the aggregate. Then, the contractor needed to replicate it to get final Landmarks approval.
Mortar patches will fail without proper preparation. The 505 LaGuardia building’s facade was somewhat tricky. The rebar placement from the original construction was in many cases too shallow—and therefore too close to the building’s surface—which made it a contributing factor for failure. Restoration would require either the removal of the rebar, readjustment of its positioning, or an application of mortar that would protrude from the profile of the building to meet the minimum required depth of 1-inch below profile.
Because of the sheer size and diameter of some of the existing rebar, it made the most sense to patch above the profile to meet the depth requirement. The typical requirement for patching in conjunction with rebar or other metal is to have one-inch minimum clearance between the surface of the patch and the metal itself. The rebar was also coated with a rust-inhibiting paint to avoid further rust jacking or rust staining.
The sheer size and diameter of some of the existing rebar is shown
The rebar’s shallow placement led to unforeseen challenges
Building features such as outside corners often required very deep patches
Once the entire building’s prep work had been inspected, the patching itself began. Even then, we encountered some surprises. During our inspections, we noticed an issue with the deeper patches (several inches in depth): our M90 mortar was being installed in layers—something required with other mortars, but not with our Jahn Mortars. Our Jahn Mortars are specifically designed to be installed in a single application regardless of depth (i.e., Jahn Mortars do not require layers).
Not ideal: the contractor was scoring the first layer and leaving the rest of the surface smooth
But the design of this particular building, with its overhanging features and outside corners and often requiring very deep patches, led us to conclude that two layers would, in fact, be a better approach for this project. And so we modified our instructions and allowed the application of the M90 Mortar in two lifts, provided the first lift was appropriately prepped for the second lift. And this is where we ran into our second problematic prep technique: the (see photo). We suggested that they use a standard mason’s brush to rough the surface. Doing so would provide a much better bonding surface than the scored lines on a smooth surface.
This process was agreed to and followed throughout the duration of the project. Today, roughly one thousand buckets of our Jahn M90 Mortar has been successfully installed at 505 LaGuardia Place. Work will most likely continue into 2023, as more areas on the building have been added to the original scope of work.
