I am posting this article as further evidence of the problems with plaster over metal lath inadequately secured by nails. Though it may have been applied over an older plaster/wood lath ceiling, the crucial failure occurred because the nails as they were used, weren't adequate to do the job.

Philip LaMachio,
Home

Inspectors poking through the rubble inside of the old Sequoia Theatre in Mill Valley could not determine Tuesday what caused the ceiling to suddenly collapse the day before on 40 people enjoying an afternoon movie.




[Child injured by ceiling collapse]

A 500- to 600-square-foot section of plaster and metal lath, a wire mesh material, crashed down 20 minutes into Monday's bargain matinee showing of "Garden State," forcing injured and frightened moviegoers to stagger out through clouds of dust and debris.




Some 29 people were injured, and three were taken to Marin General Hospital for treatment of head wounds, but none of the injuries was believed to be serious.

Investigators said it was just lucky that most of the moviegoers were in the raised section in the back of the theater, away from where the heaviest chunks fell. Thomas Ahrens, Mill Valley's chief building official, said the debris included huge chunks of heavy plaster and strips of lath 30 inches wide and 12 feet long.

The ceiling, he said, was being held up by bent nails, which after more than a half century gave out.

"I don't figure anybody has touched that ceiling since before World War II," Ahrens said. "It simply let go of the attachments that were holding it up, and this thing just peeled, like peeling paint, and fell to the seats below."

There are much better ways to attach a ceiling today, Ahrens said, but pounding a nail halfway down and bending it over was standard procedure in the 1940s.

The inspection showed no structural or roof failure, and water or moisture apparently did not contribute to the collapse, he said. Ahrens compared what happened to the dry wall in your dining room falling down and hitting your dining room table.

The 650-seat theater, home of the Mill Valley Film Festival each October, opened in 1929 and was turned into a twin theater in 1974. It was renovated again in 1999, but none of the renovations involved the ceiling, according to Ahrens.

The ceiling, however, does not appear to be original, he said. Metal lath was not widely used until the 1940s, when some work may have been done on the ceiling, he said.

"It's quite possible the original wood lath and plaster started to fail after 15 or 20 years, but at this point we're not sure," Ahrens said.
Mill Valley has asked the operator, the Century Theatres chain, to investigate thoroughly.

"We want to find out why this happened," Ahrens said. "It may be that it's just old, and it let go, but until we find out, the theater is going to remain closed."

Theater officials believe the investigation and repairs can be done in time for the film festival from Oct. 7 through Oct. 17.

"The show must go on," said Mark Fishkin, the Mill Valley Film Festival founder and director. "Until we hear more, we're just assuming we're using the Sequoia."
E-mail Peter Fimrite at pfimrite@sfchronicle.com.



Article : MILL VALLEY / Inspectors searching for cause of movie theater ceiling collapse / No structural or roof failure, city official says


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