MANCHESTER — Historic Valley Cemetery is a favorite target of vandals who get their kicks toppling granite and limestone tombstones and pushing obelisks off their bases.

Storms also have taken their toll, with falling branches damaging the antique grave markers.

Last weekend, a group of about 30 members of New Hampshire Plumbers and Pipefitters, Local 131, volunteered to set things straight, up righting grave markers and gluing together stones broken in two and putting them back in the ground, making sure to compact the dirt to anchor them in place.

Daniel Coffey, the local’s training coordinator, said some of the limestone and granite makers weighed more than 600 pounds each, requiring four to six men to lift them.

In about three hours, the construction workers had up righted and/or repaired 51 tombstones, Coffey said. Pipefitter Dave Schefer, who has a passion for history and walks the cemetery daily, said by his count the volunteers reset 84 grave markers and seven obelisks.

“It was amazing the amount of work they got done,” Schefer said of the volunteers who worked on the project last Saturday. “They were mostly apprentices, young and strong.”

Schefer asked his “union brothers” to take on the task after becoming disheartened by the vandalism, graffiti and general disrepair of the once grand garden cemetery bordered by Willow, Valley, Pine and Auburn streets.

He estimated 95 percent of the markers were damaged by vandals. Coffey said the other tombstones just deteriorated due to age and/or the weather.

Among those damaged was the grave marker of former Manchester Mayor William H. Clarke and several Civil War veterans, Schefer said.

One obelisk, weighing more than 1,000 pounds and which was toppled by a falling tree branch, proved to be too heavy to lift, but volunteers hope to return later with equipment to do the job.

Coffey said the workers broke into teams of three and set about fixing the damage. Some of the tombstones had to be dug out and set up right. Then the soil was compacted to ensure the gravestone would hold.

“We’re hoping to keep doing it,” Coffey said. “And we’re hoping to do a project at the veterans cemetery in Boscawen.”

Schefer said an autumn project might be focused on the cemetery’s English gothic chapel and a nearby fountain.

“We’d like to install a new heating system, because that’s what we do, we’re plumbers. We’ll try to get donations from suppliers and maybe have some sort of event,” said Schefer, a history buff with a particular passion for cemeteries. That could be because his first job was a grave digger.

Valley Cemetery is listed on the U.S. National Register of Historic Places and was the second garden cemetery in the nation. It is on 20 acres donated to the city in 1840 by the Amoskeag Manufacturing Corp. for use as a burial ground.

It featured carriage paths and bridges over streams and walkways and, at the time, it was fashionable for residents stroll through the garden cemetery. One section, bordered with plain iron bars instead of the elaborate iron work prominent on the Pine and Auburn streets side, was for paupers.

The cemetery is the final resting place for many of Manchester’s founding fathers and first families, including the Starks, Straws, Blodgets, Beans, Buntons and Harringtons; two New Hampshire governors; about 60 Civil War soldiers; a few veterans of the Revolutionary War; and at least one soldier from the French and Indian wars.