By Eve M. Kahn. Published: May 22, 2005. The New York Times.

A year ago, owners of condominium apartments at 241 Eldridge Street heard dire news. Cavities were forming within the brick walls of their century-old tenement, so much so that the place was held up largely by inertia.

Scott Henson, an architect whose Manhattan firm is restoring the building, offered residents two options. They could spend $1.4 million dismantling and rebuilding the decrepit walls, while protecting their apartments temporarily with wallboard and tarpaulins, or they could try a less invasive and less costly stabilization technique that had never before been used in the United States.

After examining sheaves of test reports and letters from scientists and engineers, residents voted unanimously to go with the avant-garde solution, even though it called for pumping the walls full of gray goop.

"We investigated enough to put our faith in it," said Robin Schanzenbach, president of the condo board. "We've felt we're totally on the cutting edge."

The milky chemical, whose official name is micro injection grout, is manufactured by a German company called Jahn International, and its formula is secret. From Feb. 9 to April 22, construction crews drilled 1,435 holes into the building and pumped in 1,280 gallons of the mixture. Final price tag: $106,000.

The grout filled crannies between bricks, where mortar had been crumbling into dust, and it set in half an hour. It also sometimes made a mess. A dozen times it spilled onto apartment window sills or floors, but, as David Bergman, an architect who has lived in the building since 1995, pointed out, "It cleans up very easily, with paper towels and 409 or Fantastik."

The Jahn product, which has been commonplace in Europe for 30 years, has been imported into the United States since the 1980's for small repair jobs, said Dennis Rude, chief executive of the distributor, Cathedral Stone Products. But Mr. Henson is the first customer to apply it to an entire building.

"It's a drastic solution," said Norman Weiss, a professor of historic preservation at Columbia University. "It's also a very exciting project. The idea could be applied to hundreds, maybe thousands of buildings that have problems the owners don't know about yet, or problems that have been covered with superficial repairs - that's like putting makeup on what turns out to be melanoma."

The Eldridge Street building, a neo-Renaissance style structure, was built in 1904, but although the masons apparently lavished care on the facade, which is trimmed in terra-cotta scrollwork, they skimped elsewhere. By the 1970's the structure was abandoned, condemned and used as a drug den. A gallery owner, Nicholas Logsdail, bought the blackened shell from the city, and a veterinarian, Mary Finger, moved in and rebuilt it as condominiums. Her own 1,000-square-foot loft is listed for sale at $859,000.

Next door, at 245 Eldridge Street, stands a rental building that is a twin of No. 241. Its rear and side walls are coated with gray weatherproof stucco, and show signs of cracking and sagging. Catherine Economakis, a managing agent for the building with Granite International Management, did not return calls seeking comment on the condition of the brickwork. Mr. Henson said: "We don't want to scare anybody, but we assume conditions in those walls are the same as here."