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This article provides a photo guide to identifying and installing types of plaster support systems: metal lath, wire lath, etc. that are installed in buildings. We use building ceilings and walls as a photo and investigation guide to plaster and mortar lath systems.
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.
See Plaster & Beaverboard & Drywall where we include photographs of non-plaster interior wall and ceiling coverings including drywall, beaverboard, and paneling. Also see drywall identification photos at CHINESE DRYWALL HAZARDS. For plaster type surfaces used on building exteriors, see STUCCO WALL METHODS & INSTALLATION.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Expanded metal lath has been widely used to support both interior plaster in buildings and exterior building wall stucco systems. This article explains plaster systems based on metal lath in building interiors. Also see STUCCO WALL METHODS & INSTALLATION for a discussion of exterior uses of stucco and metal lath.
At below left we show a cut-cross-section of a steel-lath supported exterior wall on a Minneapolis, MN. home. Our photo at below right shows the marks left by metal lath on felt paper that had been used as a building sheathing wrap on the same home. These details were exposed during construction work for an addition.
Details about exterior stucco and metal lath are at STUCCO WALL METHODS & INSTALLATION.
Watch 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.
Expanded Metal Lath Plaster Ceiling Catastrophic Collapse Case
As we discuss in detail at at PLASTER, LOOSE FALL HAZARDS, 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:
Frequently Asked Questions (FAQs) about about identifying & installing types of plaster lath systems
Question: which way up does the diamond lath go on walls?
How to install and apply plaster to expanded metal mesh (diamond mesh):
I have heard contradicting information about the direction of the lath. When I drag my hand from top down should the direction of the lath be biting at my hand or should it bite at my hand when I drag my hand from bottom up.
I read in one of your articles that “expanded metal lath must be installed with the correct side pointed up or the plaster will slip off when troweled on”. To me this means that my hand should drag (bite) when pulled from top down
Do you align with my interpretation and if this is your answer is your answer documented anywhere? - M.H., Construction Administrator
I agree with your surmise about the proper lath direction, but I'll also do some research and add that detail to our article when I can cite an authoritative source.
I suspect, however, that this technical point may be over-stated in that the same diamond mesh lath is used on ceilings where the direction of the mesh won't make difference in the adhesion of the plaster.
In any case it's the plaster ears or mortar keys that are formed by plaster that is pushed through the lath that make the plaster or mortar mix adhere soundly to the metal lath. That's also why metal lath that is nailed too tightly to a smooth surface with no air gap behind may not give great results.
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