High-Tech Waterproofing: There's More Than One Way to Skin a Co-op

In this case, says Ehrman, a 35-year-old Brooklynite who earned his degree from the Rochester Institute of Technology, that meant coating the walls beneath the brickwork with a high-tech waterproof layer that's reinforced with Fiberglass. It wasn't an inexpensive solution, but the buildings "have been plagued with these leaks for decades. . Many clients they have a limited budget, say a couple hundred thousand, that'll resolve all the unsafe conditions, but it wouldn't be enough to cure epidemic leaks of this magnitude." This board, after years of leaks, "wanted it fixed and this time they wanted it fixed right."

Nestled at a cul de sac in the Spuyten Duyvil section of Riverdale, 10-story building at 25 Knolls Crescent, completed in 1958, and the 11-story 55 Knolls Crescent (above; click on image to enlarge), completed in 1952, went up in the wake of its 1951 sister buildings at 60 and 80 Knolls Crescent. A separate entity from those earlier edifices, Knolls Cooperative Section II is, like Section I, self-managed by its residents. The Section I buildings, at least, and probably Section II's, were designed by the noted architectural firm S.J. Kessler & Sons, later responsible for Lincoln Towers, Washington Square Village, and many other apartment buildings through at least 1980, and constructed by Ferman Builders, Inc. (Click on architectural rendering, below, to enlarge.)

Along with routine, required Local Law 11/98 repairs, Section II had been dealing with epidemic leaks that required more extensive work. "The corners of the buildings were the areas of greatest concern," says Ehrman. "Those are locations of the most exposure, and they can also be areas of movement and expansion, and places that are most vulnerable to water infiltration. It's common for buildings of this type to need corner repair" for Local Law 11/98 compliance. "But when you couple that extreme exposure to the elements, you get a situation."

The solution was to go futuristic on its asphalt. That meant applying a relatively new type of breathable coating to what's called the CMU (concrete masonry unit) wall – the structural wall behind the exterior brickwork (called the "face brick" a.k.a. the "veneer brick." See? You always learn something here!) "The CMU at each deck supports the brickwork," Ehrman explains. At every fifth row, or "course" of bricks, a builder typically installs "a header, which means a row of bricks that tie into the CMU. That's how the brick is held to the building."

On the Section II buildings, however, "That CMU was found to be very porous. There were openings and voids and a lot of locations where water could infiltrate the building interior." So Ehrman and Rand removed the veneer brick and coated the CMU with a breathable, cementitious (cement-like) stucco product brandnamed Structural Skin (see at left), made by a Dover, N.H., company called Conproco. A base coating for exterior wall systems, designed to cover block, concrete, brick, exterior sheathing or even plywood, it comes as a powder that the contractor mixes with water onsite. After applying it, project contractor Skyline Restoration sheathed the building envelope with new brick.

"The reason we specified that product," Ehrman says, "is that it has Fiberglass reinforcement. When you look at the powder, you see these Fiberglass fibers. It makes the coating that much stronger. Normal stucco is just regular cement, so if you put a lot of force on it it'll crack – it doesn't take much. The Fiberglass fibers make this significantly stronger that regular cement coating." Other buildings that have used Structural Skin include Broadway's Lunt-Fontanne Theater and 29 W. 57th Street, the old American Piano Company building.

What happened to the old bricks? "In our specifications, we typically say the contractor is responsible for proper disposal of at least 50 percent of construction debris in an environmentally friendly manner," Ehrman says. "We've had this clause for at least a couple of years." Contractors work with what are called waste-management firms, and bricks, in particular, are easy to pulverize and have their component parts recycled.

The project, which began in September 2008, was substantially completed in March 2009, Ehrman says. Other work on the project included re-pointing mortar joints; replacing cast stone windowsills; replacing and refurbishing defective window lintels; and installing new aluminum windows. The project budget was $541,000. The 236-unit co-op obtained a $1 million line of credit from NCB in December.

55 Knolls Crescent image courtesy Rand Engineering & Architecture.