Not every block party offers guests a chance to stretch a giant slingshot and launch paint-filled balloons 130 feet into the air at a public housing high-rise.

But how often do East End residents bid a jubilant farewell to an 18-story building that is East Liberty's version of the Berlin Wall as well as a monument to substandard public housing and abysmal urban planning?

From 1:45 to 6 p.m. tomorrow, hundreds of people will use the slingshot to create a new piece of public art while celebrating the demise of East Mall, a high-rise that straddles Penn Avenue and has a date with a demolition crew in the next two weeks. The building already has been fenced off and portions of Penn Avenue closed.

"It's a way to create a new piece of public art for the day using the building as a canvas," said Ernie Hogan, director of residential real estate for East Liberty Development Inc. The celebration, he said, "signifies the start of a new beginning" for the neighborhood.

Liberty Park, another public housing high-rise, at Penn Circle and Broad Street, also is slated for demolition and both buildings will be gone by October, Hogan said.

Johnny Lee, a Swissvale resident and a doctoral student in computer science at Carnegie Mellon University, designed and built the giant slingshot with CMU fine arts student Joshua Atlas, 21, of Squirrel Hill. The two men met in a class where Atlas was a student and Lee was a teaching assistant.

"There aren't that many 18-story tall art monuments in the country. I don't know if we're going to get enough paint on it to turn it into a piece of art but the concept is there. It's only going to be up there for a day or two," Lee said in a telephone interview yesterday.

Jennifer Sinfelt, associate director of Friendship Development Associates, said East Mall "really kind of serves as a wall, cutting East Liberty off from the East End. Bringing that barrier down is really going to connect the communities more."

The event may lack the explosive impact onlookers saw when Three Rivers Stadium became rubble but, Sinfelt said, East Mall could not be imploded because of potential damage to city water and sewer lines.

Nonetheless, "Get Down!" is the name for tomorrow's party, which will be a bittersweet event for some former East Mall residents who have moved to other housing but plan to attend, Sinfelt said.

"Get Down!" also is the featured event of Unblurred, a monthly open house hosted by the Penn Avenue Arts Initiative to showcase the work of new young artists, including dancers, iron forgers and painters. Whole Foods, Giant Eagle and Shop 'n Save will serve food and drinks.

A stage at Penn Avenue and Beatty Street will feature performances by the band House of Soul, dance troupe Nego Gato Capoeira, Gong Lung Sing Si Deui (Steel Dragon) Dance Team and Davu, a spoken word artist.

Lee and Atlas have tested their slingshot in an abandoned Wilkinsburg parking lot. Lee estimates that if four people pull back the sling, the 17-inch balloons filled with paint should travel at just over 90 mph. The two men used a video camera to photograph their tests.

"They have assured us that it is engineered soundly. There shouldn't be misfires. I don't think paint on people will be an issue," Sinfelt said.

The slingshot, which is 25 feet wide and 25 feet tall, will arrive on two 44-foot-long telescoping boom lifts that are normally used in construction.

"Some of it will stick to the building. Some will go back to the street level. Someone is in charge of getting tarps for the street or will hose off the street afterward," Lee said.

Lee used 200 feet of half-inch diameter surgical latex tubing to create the slingshot.

"I'm currently under the impression that the mayor wants to fire the first shot," Lee said.