Plaster lath board © Daniel Friedman Loose Plaster Ceiling & Wall Hazards: Falling Plaster Injury Risk
     

  • PLASTER, LOOSE FALL HAZARDS - CONTENTS: Loose plaster & plaster lath - how to identify & evaluate the hazard. Plaster System identification and history of use. Photo guide to plaster coatings, cracks, bulges, hazards. Plaster ceiling collapse hazards & photographs.
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Loose or collapsing plaster ceiling hazards: here we provide a photo guide to identifying types of plaster installed in buildings, using building ceilings as a photo and investigation guide. In this article series we describe and discuss the identification and history of older interior building surface materials such plaster, plaster board, split wood lath, sawn lath, and expanded metal lath, Beaverboard, and Drywall - materials that were used to form the (usually) non-structural surface of building interior ceilings and walls.

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Loose Plaster is Unsafe, Especially Loose, Falling Plaster Ceilings

Plaster lath board © Daniel FriedmanWatch out: for loose plaster that can fall and injure building occupants.

If ceiling plaster is bulged and moves when you apply gentle pressure to it, chances are that the plaster keys, the protruding plaster that oozed between the plaster lath strips to mechanically secure the plaster surface in place, have broken off.

On the other hand, some "bulged"-looking plaster may be soundly secured, as we describe at PLASTER BULGES & PILLOWS.

Wood Lath Ceiling Collapse Photographs

Our loose plaster photo at below left shows wall plaster that was quite loose and whose plaster ears had broken away. Some renovators use the term "rotted plaster" or "rotten plaster" but of course since we're talking about a cementious material, not organic wood, "rot" is a euphemism for deteriorated.

Our loose plaster ceiling photo (below right) shows an unsafe building ceiling at risk of falling.

Plaster lath board © Daniel Friedman

 

Plaster in this condition can easily fall away. While small areas of loose plaster can be successfully re-adhered using plaster washers and screws, a better (but more costly) repair is to remove the loose plaster entirely and re-plaster the section properly.

At below are two photographs of plaster ceilings in the attic that has already fallen away in two older homes. You may also enjoy noticing the pit-sawn kerf marks on some of the plaster lath of this older home in the photo at below left, and the hand-wrought iron hook in the photo at right. .

Plaster lath board © Daniel Friedman Plaster lath board © Daniel Friedman

Watch out: often the framing supporting plaster ceilings in homes built before 1900 was sized to be just strong enough to support the weight of the plaster itself. Such ceiling structures were not intended to support the weight of a curious home owner or home inspector.

Expanded Metal Lath Plaster Ceiling Catastrophic Collapse Case

Plaster ceilings in newer buildings are not immune from collapse either, as you'll see by the catastrophic ceiling collapse shown just below. This plaster ceiling was applied on expanded metal lath. The lath was wired to steel pipes or bars that in turn were hung from a smaller number of steel supports. The final steel supports were hung from wire ties connected to fasteners that had been "pin-shot fasteners" shot into the sides of concrete ceiling joists.

The combination of several factors led to this ceiling collapse:

Plaster lath board © Daniel Friedman Plaster lath board © Daniel Friedman

The combination of several factors led to this ceiling collapse:

  • An insufficient number of fasteners was used to secure the whole suspended ceiling structure to the concrete beams above - considerably less than called for the industry standards including those of the Hilti Corporation, a producer of pin shot fasteners. This was the most apparent and most significant cause of this ceiling collapse in our opinion.
  • The pin shot fasteners used as ceiling hangers may have been of the wrong type for this application and may have been improperly loaded.
  • It is possible that the shot fasteners used to provide fasteners for the wire hangers supporting the ceiling were not properly installed, allowing some of them to separate from the concrete. For example if pins were shot directly "up" into the underside of joists or beams when they were intended to be shot into beam or joist sides, they may have lacked sufficient friction to remain in place, being later pulled out from the downward force of the weight of the ceiling.
  • There was no perimeter support for the ceiling.
  • We considered the possibility that damp conditions in the building may have contributed to fastener loosening or deterioration, but the absence of rust in the field photos argues against that factor.
  • Nearby demolition for building renovation work created vibrations sped or precipitated this collapse that could have occurred at any time.

Typical Design & Construction of Suspended Plaster Ceilings

According to Van Den Branden and Hartsell, a typical suspended wire-mesh based plaster ceilings using hangers, carriers, and furring channels (such as described by Inland Steel Products Co.,) typically used No. 8 galvanized wire, though other wire sizes, rods, and flat iron were also used:

  • #8 galvanized wire. Wire in gauges 12,10, 9, 8, 7, and 6 sizes. Common #8 steel wire is rated to carry 16 sq.ft. of completed ceiling per hanger (presuming that the ceiling weight and thickness are also to standard specifications).
  • 3/16" pencil rod suspended ceiling hangers
  • 1" x 3/16" flat iron suspended ceiling hangers

Fasteners for suspended plaster ceilings: None of VanDenBranden/Hartsell's hanger examples included pin-shot fasteners, though that may be due to the age of the text. They describe

  • Hangers attached to concrete slabs (overhead ceilings) by looping and embedding wire in the concrete (obviously installed during original construction)
  • Securing suspended ceiling hangers to inserts cast into the concrete
  • Suspended from wood joists by drilling holes 3" or more above the joist bottom
  • Suspended from wood joists by nailing 16d spikes through the joist [center]

Also see BUILDING SAFETY HAZARDS GUIDE for more building hazards of particular concern to homeowners or building contractors, building inspectors, and home inspectors.

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